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This Nissan Cube has a little yellow light on 
its dashboard which says

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"Service Engine Soon."

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That's its version of a check engine light, 
which is more formerly known as the MIL

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which stands for mother-in-law—

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I mean, malfunction indicator lamp.

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And as its name implies, that means something's wrong with this car.

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What's wrong?

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Well, a quick check with one of those Bluetooth code scanners revealed its engine computer has stored the dreaded fault code

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P0420, catalyst system efficiency below threshold.

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In other words, this car thinks its catalytic converter isn't working right.

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And because of that, it would fail an emissions test if I were to take it in for one,

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which I'll have to do before 
I can renew its registration.

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But what exactly is the catalytic converter?

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What does it do?

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And how can the car tell it's not working right?

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Well...

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[motor and hydraulic pump whining]

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[ratchet wrench sounds]

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...this is the catalytic converter.

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Why is it here on the desk?

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We'll get to that.

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As you can see, it's actually quite simple.

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It's basically just a section of exhaust pipe which has a couple of expanded sections

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that are filled with a tightly-packed grid of ceramic material.

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And the engine exhaust flows through those grids before it's released to the atmosphere.

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That ceramic material is coated with precious metals: 
usually platinum, with a bit of rhodium and palladium for garnish.

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Which is why these things are so expensive and often stolen.

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The precious metals form a Catalyst that Converts 
smog- and acid rain-forming nitrogen oxides

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into plain old nitrogen and carbon dioxide.

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It will also convert any unburnt hydrocarbons from 
imperfect combustion into carbon dioxide and water vapor.

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In other words, this thing's job 
is to make engine exhaust as harmless as possible.

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But it doesn't work on its own.

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In fact, the chemical reactions which occur inside of here rely on a wildly complicated series of sensors, actuators, and feedback loops

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which the car's engine computer is orchestrating on a second by second basis.

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Now, this is a very ordinary car.

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Okay, well, not really.

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It's a Nissan Cube!

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But I mean it's a 15-year-old economy car which has nothing you might call "advanced technology" under the hood.

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In fact, this one even has a manual transmission.

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But I'll bet a lot of you watching are going to be very surprised by just how much stuff is going on in this barebones base model

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every time you turn its key, start the engine, and drive it.

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This engine, the Renault-Nissan MR18DE, is the 
1.8 L 4-cylinder engine which powers the car and makes it move.

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But the engine itself is 
little more than a complicated air compressor.

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This engine cannot do anything 
without this little computer box running the show.

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This is the engine control module, and it controls... everything!

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From the spark plugs to the fuel injectors — even the throttle!

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This car's gas pedal is just a fancy joystick telling the computer how far you've pressed it down.

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And this has been the normal reality of cars for quite a long time.

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This video is the first in a series on engine 
management technology,

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and while we're going to be exploring a lot of things today to understand the catalytic converter,

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I'll only be scratching the surface 
and there will be much more to come.

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So, first of all...

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is that one of those progress bars that shows up when people do ad reads?

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On this channel?

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I'm gonna have to put my foot down on that.

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Ooh, are those Technology Connections socks?

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Yes, they are!

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That's right, there is now 
for the first time official TC merch for sale.

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But... this is only sort of an ad read.

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See, I won't be making a scent from the sale of these socks.

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In fact, all of the profit they generate will go to charity.

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If this sounds familiar to some of you, well, that's because it's a collaboration with the Awesome Socks Club and Good Store.

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I've been a member of the 
Awesome Socks Club since its inception.

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I love silly socks and haven't worn normal socks in years.

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So, when Hank Green decided 
to start a sock subscription service,

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I signed up right away 
and have been a happy customer ever since.

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And I am both thrilled and honored to announce that

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Hank and his team worked with me to make Technology Connections a part of it.

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For the next two weeks and two weeks only,

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you can sign up for a limited run of socks designed by independent artists based on my weird ideas.

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They'll arrive at your door monthly 
starting in January with free worldwide shipping,

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and since they come in pairs, that means each month you too will experience the Magic of Buying Two of Them!

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We're offering both a full year of socks as a prepaid subscription

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and a six-month option if that works better for you.

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These are just some of the designs we've cooked up - the rest will be a fun surprise!

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And not only will you get some great socks,

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but you'll be helping Partners in Health fund and operate the Maternal Center of Excellence in Sierra Leone.

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This world-class facility provides exceptional 
medical care to mothers and children

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in a region with one of the 
highest maternal mortality rates in the world.

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If some silly socks which help people sound like your cup of tea,

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there will be information in all the places on how to get them.

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Thanks for your attention and now back to the show.

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So first of all, what is the job of this engine?

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Well, very basically, it's to turn a fuel into physical force which we can use to make things happen.

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Like push a car along a road.

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Like most internal combustion engines, this uses pistons traveling up and down cylindrical combustion chambers

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which are attached to a crankshaft to translate their up and down motion into a spinning motion.

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Valves at the top of the combustion chamber open and close in time with the movement of the pistons

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and through filling the chambers with a basically explosive mix of air and fuel as the pistons move downward,

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then compressing that mixture as the pistons move back up

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and then igniting it with a spark plug once it's at the top, the rapidly expanding mixture of hot gas will force the pistons back downward

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and thus the chemical energy in the fuel is converted to mechanical energy.

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Now, as far as explaining 
the mechanical parts of the engine,

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that's actually as far as I'm going to go today.

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There's a lot of stuff in here that's really interesting, and I'll be tearing this apart in future videos to show you all of it.

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But for now, I just want to focus on where air goes in and exhaust comes out.

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This large plastic series of tubes is the intake manifold and it delivers fresh air to each of the four cylinders through the cylinder head.

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Fuel is mixed in by electronic fuel injectors which live underneath the intake manifold

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and spray it into the airstream as the cylinders ingest air.

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After the fuel is burned in the cylinders, the resulting hot exhaust is pushed out the other side of the cylinder head and into the exhaust manifold.

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The catalytic converter bolts to the engine right here.

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It needs to be as close to the engine as possible because the catalyst has to be very hot in order to function.

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And we need this to function 
because of what happens when we burn gasoline.

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Or rather, what never happens quite correctly.

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But before I explain that, have you ever seen 
what burning a tablespoon of gasoline looks like?

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Neither have I, but I'm an adult 
with access to tablespoons and gasoline.

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So, I wanted to find out.

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It looks like this!

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And this flame burned for about 3 minutes.

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But you know how long it takes this Nissan Cube to go through a tablespoon of gasoline when driving 60 mph?

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Seven seconds.

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This car gets 30 miles per gallon on the highway,

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which means it burns through gasoline at a rate of 
8.53 tablespoons per minute when traveling 60 mph.

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And have you ever seen what burning 
8 tablespoons of gasoline looks like?

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Neither have I, but it looks like this!

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This is what's going on inside the engine of this car 
when you're driving it at highway speeds.

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In fact, this is only about half as much because even with the added heat from the other tablespoons helping the gasoline evaporate more quickly,

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it still took about 3 minutes for 
all this to burn away.

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Now, I know it doesn't seem like you're setting fire to gasoline when you drive a car, but you are in fact burning it

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and faster than you see here.

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Now imagine millions of cars are doing this all at the same time.

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Yeah.

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All that smoke and crap is why we spend so much 
effort making sure the internal combustion engine  

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burns gasoline as cleanly as it can.

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And the catalytic converter 
is a hugely important part of that goal.

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But before this thing even gets involved, 
we need to play with chemistry.

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The chemical reaction which occurs inside the engine requires oxygen from the air for combustion.

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The oxygen combines with the hydrocarbons which make up the fuel and the result should simply be carbon dioxide and water vapor.

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Now each molecule of fuel requires a certain number of oxygen molecules for combustion to happen completely.

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This is the basis of the air/fuel 
mixture we feed into the cylinders.

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If you don't have enough oxygen, the fuel won't burn completely and you'll get unburnt fuel in the exhaust,

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which is not good.

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But if you have too much oxygen, the combustion happens at higher temperatures which lead to nitrogen oxides forming.

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And that's also not good.

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Both unburnt fuel and nitrogen oxides contribute to the formation of smog and acid rain in the atmosphere.

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So ideally we want the engine 
to have the exact number of oxygen molecules present in its cylinders

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for the quantity of fuel which is about to be burned.

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If we can manage that, 
we'd have what's called stochiometric combustion.

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Since gasoline is gasoline and air is air, we actually know the air-to-fuel ratio that results in stochiometric combustion.

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For gasoline, it's a 14.7:1 ratio of air to fuel by mass.

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In the old days, we tried our best to achieve that ratio using a carburetor.

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And we still do actually for lots of small engine equipment.

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Carburetors are extremely simple.

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Basically, you're just running air past a tube with some liquid gasoline in it,

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and the venturi effect causes it to join the airstream.

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Then, gasoline's volatile nature means it quickly becomes a vapor on its way into the engine.

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If properly dialed in, you can get a carburetor to put out a pretty consistent ratio of fuel to air no matter how much air flies through it,

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which is extra useful because then you can control the power an engine produces simply through restricting its air flow.

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That's what the throttle does.

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When it's closed down, less air can get to the engine 
which, in the case of a carbureted engine,

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also means less fuel is delivered and thus less power is produced.

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And as the throttle opens, the engine gets more air and the carburetor delivers more fuel, which results in more power.

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All with a consistent air-to-fuel ratio.

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But well, the world isn't quite so simple.

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For a start, there are situations such as acceleration 
where the engine is under a heavy load

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where we actually need a rich fuel mixture
 to prevent the engine from running too hot.

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And that will let unburnt fuel into the exhaust system.

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But even if we could always run the engine stoichiometrically, combustion inside the cylinders is never perfect.

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The world is too random and 
the pistons are moving too fast.

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So even if you know you've got exactly the correct number of fuel molecules to oxygen molecules,

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you're always going to end up with either some unburnt fuel or some nitrogen oxides or potentially both.

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And that's what the catalytic converter is designed to fix.

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By passing the exhaust through this grid 
of precious metal-coated material,

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nitrogen oxides are reduced to pure nitrogen and unburnt fuel as well as carbon monoxide are oxidized into carbon dioxide.

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When properly operating, the catalytic converter will all but 
eliminate harmful pollutants from the engine.

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Except for carbon dioxide, of course...

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but sadly, we're still having trouble 
convincing some people that's a problem.

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Catalytic converters became 
more or less required in cars sold in the US back in 1975,

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but the earliest ones didn't deal with nitrogen oxides.

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Those so-called two-way converters only handled carbon monoxide and 
unburnt fuel -

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which was a tremendous help for air pollution!

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But nitrogen oxides still contribute to smog and acid rain.

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So shortly thereafter, we got three-way 
catalytic converters which is what this is.

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And if you're wondering why we don't talk about 
acid rain much anymore, these are a big part of why.

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But with these three-way converters, 
we have a new can of worms.

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You can't just stick one of these in a car and expect it to work.

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The chemical reactions the catalyst promotes require the engine to be hovering around the stoichiometric point.

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00:14:01,815 --> 00:14:07,673
"Hovering around," incidentally, 
is a fine example of foreshadowing.

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00:14:07,673 --> 00:14:11,381
Anyway, if the engine is running too rich or too lean,

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not only will the catalyst stop functioning, 
but if those incorrect conditions go on for too long,

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the catalyst itself can be damaged.

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This sounds like a pretty big problem.

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But, what if we could actually monitor and control the combustion process happening inside the engine in real time?

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00:14:29,839 --> 00:14:38,041
That would allow us to adjust the engine's air/fuel mixture on the fly and make sure it's right for the catalytic converter.

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00:14:38,041 --> 00:14:44,917
Well, that's exactly what we do and is the main reason we started having a computer run the show.

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00:14:44,917 --> 00:14:49,461
Now, in the interest of time, I'm going to skip over all the wacky ways we used to do this

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like computer-controlled carburetors 
with fresh air injection systems.

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00:14:53,830 --> 00:14:59,029
By 1990, we had almost entirely 
moved on to electronic fuel injection systems

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00:14:59,029 --> 00:15:02,294
very similar to the one we find in the Cube.

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00:15:02,294 --> 00:15:07,356
And speaking of the Cube, let's take a closer look 
at what it's doing as the engine runs.

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Since this car was made after 1996 —

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again, nothing about this is new —

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it has the standard OBDII port under the dashboard
which lets scan tools talk to the engine computer.

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00:15:20,137 --> 00:15:23,228
OBD stands for onboard diagnostics

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00:15:23,228 --> 00:15:29,037
and this interface became standardized because engine computers are able to monitor the emissions equipment for issues.

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00:15:29,120 --> 00:15:31,562
And plenty of other things, too.

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00:15:31,562 --> 00:15:36,235
Now, these days, you can pick up 
a Bluetooth code scanner for about 20 bucks.

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00:15:36,235 --> 00:15:40,586
And honestly, if you drive a car, 
it's probably worth having one of these.

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This scanner, along with 
the smartphone app you use it with,

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00:15:43,719 --> 00:15:47,430
can not only show you 
what trouble code is causing a check engine light,

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but they can provide enough information to diagnose lots of issues, including the P0420 code the Cube has.

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00:15:54,367 --> 00:15:58,548
But for this video series, 
I wanted something a little more powerful.

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So, I picked up a proper scan tool!

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00:16:02,375 --> 00:16:07,015
Which is really just an Android tablet 
talking to a suspiciously similar Bluetooth dongle...

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00:16:07,015 --> 00:16:12,711
But this scan tool can speak the proprietary languages that Nissan and all the other manufacturers use

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00:16:12,711 --> 00:16:15,500
to hide certain data and functions.

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00:16:15,500 --> 00:16:18,534
And I can screen record with it so you can see what I can see!

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00:16:18,534 --> 00:16:22,730
For now, I'm just going to use the standard OBDII protocols.

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00:16:22,730 --> 00:16:30,969
After selecting live data, the scan tool goes through the parameter IDs or PIDs the engine computer makes available to it.

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00:16:30,969 --> 00:16:34,214
And once it has its list, we can go through it.

211
00:16:34,214 --> 00:16:38,186
This is just some of the data the engine computer is collecting.

212
00:16:38,186 --> 00:16:43,134
But I want to call out this: 
air flow rate from mass air flow sensor.

213
00:16:43,134 --> 00:16:47,252
Remember that the cylinders 
are being fed air from the intake manifold.

214
00:16:47,252 --> 00:16:52,413
And if we follow that back, 
we'll find that a hose connects it to the air filter housing.

215
00:16:52,413 --> 00:16:59,279
Combustion air is passed through a filter to make sure the engine doesn't ingest things like dust or sand which could damage it.

216
00:16:59,279 --> 00:17:04,284
But between the filter housing 
and the throttle is the mass air flow sensor.

217
00:17:04,284 --> 00:17:11,739
This is a sensor which can tell the computer exactly how much air the engine is ingesting in real time.

218
00:17:11,739 --> 00:17:17,753
There are various types of mass air flow sensors and some engines use a different technique altogether.

219
00:17:17,753 --> 00:17:23,797
But the computer will use this sensor to calculate how much air the engine is actually ingesting.

220
00:17:23,797 --> 00:17:29,615
That data along with data provided by other sensors which measure things such as the intake air temperature,

221
00:17:29,615 --> 00:17:37,919
engine coolant temperature, and more is enough information for the computer to run the engine in what's called open loop control.

222
00:17:37,919 --> 00:17:43,175
Once the computer knows how many 
grams of air are going into the engine per second,

223
00:17:43,175 --> 00:17:47,167
it can calculate the correct 
amount of fuel to deliver to the cylinders

224
00:17:47,167 --> 00:17:51,728
in order to achieve ideal combustion 
for the current operating conditions.

225
00:17:51,728 --> 00:17:55,602
And it can meter precisely how much fuel will be injected

226
00:17:55,602 --> 00:18:04,837
by varying the length of time the fuel injectors are spraying fuel during each intake stroke - down to the hundredth of a millisecond.

227
00:18:04,837 --> 00:18:11,462
But all those sensors, while they can give the computer enough information to make the engine run reasonably well,

228
00:18:11,462 --> 00:18:15,612
can't tell it if its calculations were actually correct.

229
00:18:15,612 --> 00:18:20,549
For instance, when the engine is cold, 
gasoline doesn't vaporize as well.

230
00:18:20,549 --> 00:18:25,443
And while the computer will use the engine coolant temperature sensor to try and compensate,

231
00:18:25,520 --> 00:18:28,150
that sensor is only so accurate.

232
00:18:28,150 --> 00:18:32,798
Plus, gasoline is not chemically identical from tank to tank.

233
00:18:32,798 --> 00:18:39,794
Just because 2.51 milliseconds of injection time at idle with the engine hot is correct for one tank of gas

234
00:18:39,794 --> 00:18:42,962
doesn't mean it's going to be correct for the next one.

235
00:18:42,962 --> 00:18:47,320
To allow the computer to 
check its homework, we need an oxygen sensor.

236
00:18:47,712 --> 00:18:49,719
And that's what this is.

237
00:18:49,719 --> 00:18:53,568
As you can see, this thing 
is installed in the car's exhaust manifold

238
00:18:53,568 --> 00:18:58,584
and its sensing probe is exposed 
to the exhaust gases coming from the engine.

239
00:18:58,584 --> 00:19:01,191
There are two types of oxygen sensors,

240
00:19:01,191 --> 00:19:05,562
and the Cube has both of them, which is slightly annoying for the purposes of demonstration,

241
00:19:05,562 --> 00:19:11,857
but the important thing is these can confirm whether the engine is actually running stoichiometrically.

242
00:19:11,857 --> 00:19:14,607
The sensors themselves are really interesting.

243
00:19:14,607 --> 00:19:20,971
They function based on what's called a Nernst cell which produces a voltage as oxygen molecules flow through it-

244
00:19:20,971 --> 00:19:23,855
sort of like a very strange battery.

245
00:19:23,855 --> 00:19:30,971
The difference in oxygen concentration between the exhaust and the surrounding air is what will generate that voltage.

246
00:19:30,971 --> 00:19:36,254
The simpler narrowband sensor outputs a voltage that fluctuates between 0 and 1 volt

247
00:19:36,254 --> 00:19:42,568
with voltages below half a volt indicating a lean fuel mix due to excess oxygen in the exhaust,

248
00:19:42,568 --> 00:19:50,307
and voltages above 0.5 indicate that the fuel mixture is rich because there's absolutely no oxygen left.

249
00:19:50,307 --> 00:19:54,373
But it can't really do anything but indicate rich or lean.

250
00:19:54,373 --> 00:19:57,046
The midpoint is too fuzzy.

251
00:19:57,046 --> 00:20:02,016
This, though, is a wideband oxygen sensor 
which can be made much more precise.

252
00:20:02,016 --> 00:20:04,582
But... it's a little more complicated.

253
00:20:04,582 --> 00:20:09,231
The specifics aren't worth getting into for lots of reasons — there's many types out there —

254
00:20:09,231 --> 00:20:17,476
but the upshot is that the actual oxygen concentration in the exhaust results in the computer calculating a specific voltage value.

255
00:20:17,476 --> 00:20:21,905
But the oxygen sensor doesn't start working right away.

256
00:20:21,905 --> 00:20:26,938
It needs to be very hot 
in order to correctly measure oxygen concentration.

257
00:20:26,938 --> 00:20:32,489
That's why each time the engine is started, 
the computer runs in open loop control.

258
00:20:32,489 --> 00:20:36,001
But once the oxygen sensor is hot enough and it starts responding,

259
00:20:36,001 --> 00:20:42,152
which in any reasonably modern car happens quite quickly with the help of an electric heater built into the sensors,

260
00:20:42,152 --> 00:20:45,897
the computer can switch to closed loop control.

261
00:20:45,897 --> 00:20:51,500
It will still be using data from all of its other sensors to calculate how much fuel to deliver right now,

262
00:20:51,500 --> 00:20:58,713
but it will adjust its calculations based on feedback from the oxygen sensor after it's been burned.

263
00:20:58,713 --> 00:21:06,109
In this case, when the oxygen sensor data PID shows 2.24 volts,
the engine is running stoichiometrically.

264
00:21:06,109 --> 00:21:13,109
And so, the engine computer can tell in real time if it's delivering too much or too little fuel and then adjust the fuel mixture to compensate.

265
00:21:13,109 --> 00:21:19,822
And by the way, if this sounds complicated - yeah, it is!

266
00:21:19,822 --> 00:21:23,329
The conditions the engine will see are constantly different.

267
00:21:23,329 --> 00:21:29,067
One moment you're cruising at a steady speed on the highway and the next moment you're downshifting to pass someone,

268
00:21:29,067 --> 00:21:32,760
increasing engine RPM and the total load.

269
00:21:32,760 --> 00:21:41,287
Sometimes you're starting the engine when it's already hot and other times you're starting it from cold when it's -10° outside.

270
00:21:41,287 --> 00:21:48,563
There is some really fascinating logic inside this box which is essentially logging how the oxygen sensor responds

271
00:21:48,563 --> 00:21:56,625
under those various conditions to establish a long-term fuel trim profile based on all the other sensors.

272
00:21:56,625 --> 00:22:01,529
This allows the engine to have 
a very nuanced open loop control profile

273
00:22:01,529 --> 00:22:06,638
which keeps the engine in check 
even if one day the oxygen sensor were to fail.

274
00:22:06,638 --> 00:22:10,544
Though of course the computer can detect an issue with the oxygen sensor

275
00:22:10,544 --> 00:22:15,530
and will set a fault code 
which turns on the check engine light if that happens.

276
00:22:15,530 --> 00:22:19,750
But the oxygen sensor itself is also used to detect other issues.

277
00:22:19,750 --> 00:22:25,502
Say for instance one day the oxygen sensor 
sees a very different oxygen concentration

278
00:22:25,502 --> 00:22:32,986
which causes the computer to perform fuel trim adjustments that deviate wildly from the stored fuel trim profile.

279
00:22:32,986 --> 00:22:39,594
That indicates something has gone wrong 
and the computer will set a fault code if it deviates too much.

280
00:22:39,594 --> 00:22:41,447
But speaking of fault codes,

281
00:22:41,447 --> 00:22:45,455
the only code that's in this car is P0420.

282
00:22:45,455 --> 00:22:50,809
This means its computer can't find anything wrong with the engine or the fuel injectors or the oxygen sensors...

283
00:22:50,809 --> 00:22:52,856
in fact, any of the sensors.

284
00:22:52,856 --> 00:22:57,368
but it does think this catalytic converter ain't working.

285
00:22:57,368 --> 00:22:59,993
How can it be so sure of that?

286
00:22:59,993 --> 00:23:05,488
Well, the catalytic converter 
is being monitored by a second oxygen sensor.

287
00:23:05,488 --> 00:23:06,938
That one.

288
00:23:06,938 --> 00:23:13,053
By measuring the oxygen 
concentration in the exhaust after it has passed through the catalytic converter,

289
00:23:13,053 --> 00:23:18,577
the computer can determine 
how much converting is catalactually happening.

290
00:23:18,577 --> 00:23:24,052
And the reason it can do that goes back 
to that "hovering around" thing I mentioned earlier.

291
00:23:24,052 --> 00:23:31,278
Let's take a look at this website I found which lists the chemical reactions which happen inside the catalytic converter.

292
00:23:31,278 --> 00:23:37,454
Notice that in order to oxidize any unburnt fuel, 
we need oxygen available to the catalyst.

293
00:23:37,454 --> 00:23:41,361
Sounds easy. Just run the engine a little bit lean, right?

294
00:23:41,361 --> 00:23:43,500
Well, we could.

295
00:23:43,500 --> 00:23:48,276
But notice that in order for the nitrogen oxides to be reduced to nitrogen,

296
00:23:48,276 --> 00:23:52,238
we need carbon and carbon monoxide to be available.

297
00:23:52,238 --> 00:23:57,176
Which only happens when the fuel mixture is a little bit rich.

298
00:23:57,176 --> 00:24:02,127
But then we won't have any oxygen left, 
so we can't oxidize the excess fuel.

299
00:24:02,127 --> 00:24:07,544
This feels like a catch 22, so... how is this supposed to work?

300
00:24:07,544 --> 00:24:12,909
Well, the engine computer 
isn't actually trying for perfect combustion.

301
00:24:12,909 --> 00:24:21,055
Instead, in closed loop control, it deliberately oscillates 
between a little bit rich and a little bit lean.

302
00:24:21,055 --> 00:24:23,911
It needs to be close to stochiometric combustion,

303
00:24:23,911 --> 00:24:29,844
but for the catalytic converter to promote 
both reactions, it can't stay there.

304
00:24:29,844 --> 00:24:35,098
The teeter tottering it does means that when the engine is running a little lean,

305
00:24:35,098 --> 00:24:41,778
there are free oxygen molecules in the exhaust 
which the catalyst will absorb and hold onto.

306
00:24:41,778 --> 00:24:46,313
Then when the engine computer switches 
back to a slightly rich mixture,

307
00:24:46,313 --> 00:24:50,060
we get the inputs we need to reduce 
nitrogen oxides.

308
00:24:50,060 --> 00:24:56,566
And the stored oxygen in the catalyst will then oxidize whatever excess unburnt fuel remains

309
00:24:56,566 --> 00:25:00,815
after the nitrogen oxide reduction reactions are complete.

310
00:25:00,815 --> 00:25:05,567
We can actually observe 
the engine computer causing these oscillations.

311
00:25:05,567 --> 00:25:08,288
At least... sort of.

312
00:25:08,288 --> 00:25:12,582
This is why the Cube's wideband sensor is a little annoying.

313
00:25:12,582 --> 00:25:20,354
Here I'm graphing both the voltage from the oxygen sensor and 
the calculated equivalence ratio as I drive the car.

314
00:25:20,354 --> 00:25:24,022
An equivalence ratio of one would be stochiometric.

315
00:25:24,022 --> 00:25:28,759
But you can see that we're never 
actually sitting on one for very long at all.

316
00:25:28,759 --> 00:25:32,451
It keeps going a little high then a little low.

317
00:25:32,451 --> 00:25:34,719
But this is just data from the oxygen sensor.

318
00:25:34,719 --> 00:25:39,637
Here we can see the equivalence ratio the computer is actually trying for.

319
00:25:39,637 --> 00:25:43,219
And as you can see, it's not shooting for one.

320
00:25:43,219 --> 00:25:45,520
It's constantly going back and forth.

321
00:25:45,520 --> 00:25:48,071
First lean to charge the catalyst with oxygen,

322
00:25:48,071 --> 00:25:51,928
then rich to provide the inputs needed to reduce nitrogen oxides,

323
00:25:51,928 --> 00:25:55,664
and then back to lean to 
get more oxygen to the catalyst.

324
00:25:55,664 --> 00:26:01,616
Incidentally, if you've ever heard that 
catalytic converters get very hot, this is why.

325
00:26:01,616 --> 00:26:05,554
Unburnt fuel still has energy in it, 
and when the engine is running rich

326
00:26:05,554 --> 00:26:10,982
the oxidation reactions which 
take place inside the catalytic converter release that energy.

327
00:26:10,982 --> 00:26:13,488
So it gets real toasty in there.

328
00:26:13,488 --> 00:26:20,880
Now, do you see how we could use this second oxygen 
sensor to determine if the catalyst is actually working?

329
00:26:20,880 --> 00:26:25,768
Since the catalyst holds onto the oxygen that comes from the engine when it's running lean,

330
00:26:25,768 --> 00:26:34,027
and then that oxygen is used inside the catalyst to oxidize any unburnt fuel when the engine switches back to running rich again,

331
00:26:34,027 --> 00:26:41,616
if the catalyst is actually functioning, 
very little detectable oxygen should make it to this sensor.

332
00:26:41,616 --> 00:26:45,918
It should be used up before the exhaust makes it to this point.

333
00:26:45,918 --> 00:26:54,863
So, this oxygen sensor should not be able to see the switching between rich and lean the engine computer is doing.

334
00:26:54,863 --> 00:27:00,138
It should always see what 
looks like rich conditions without any oxygen.

335
00:27:00,138 --> 00:27:03,094
If this can detect the engine computer's oscillations,

336
00:27:03,094 --> 00:27:09,498
that means the oxidation reactions which should be happening in the catalyst are no longer occurring.

337
00:27:09,498 --> 00:27:13,939
Or, at least, they're not occurring as completely as they should.

338
00:27:13,939 --> 00:27:21,082
This indicates the catalyst 
is losing oxygen storage capacity and thus has lost efficiency.

339
00:27:21,082 --> 00:27:25,653
And that is why this car has a P0420 trouble code.

340
00:27:25,653 --> 00:27:30,249
This downstream oxygen sensor 
is able to see too much oscillation,

341
00:27:30,249 --> 00:27:33,194
which indicates the catalyst isn't working.

342
00:27:33,194 --> 00:27:36,923
Now, some detected oscillation is okay.

343
00:27:36,923 --> 00:27:40,483
If you remember that the trouble code said "below threshold,"

344
00:27:40,560 --> 00:27:44,760
that's because the logic 
in the engine computer is a little lenient.

345
00:27:44,760 --> 00:27:51,559
After all, when the engine runs rich for a while during a burst of acceleration, the catalyst will run out of oxygen.

346
00:27:51,559 --> 00:27:58,574
And thus once back to normal engine loads, the computer needs to recharge it by running the engine lean for a while.

347
00:27:58,574 --> 00:28:02,157
And that process isn't necessarily going to work on the first try.

348
00:28:02,157 --> 00:28:04,914
The computer's not in control of this thing.

349
00:28:04,914 --> 00:28:10,000
So, the downstream sensor 
may mirror the upstream sensor for a short time.

350
00:28:10,640 --> 00:28:14,244
This is a long way of saying that before I 
condemn the catalytic converter,

351
00:28:14,244 --> 00:28:20,504
it's important to actually see what the downstream oxygen sensor's output looks like while driving.

352
00:28:20,504 --> 00:28:23,823
So, I need to take it for a test drive.

353
00:28:23,823 --> 00:28:25,372
Okay, so here's what's going on:

354
00:28:25,372 --> 00:28:32,600
I have the scan tool configured to graph the voltages from both of the oxygen sensors, and it will also show vehicle speed.

355
00:28:32,600 --> 00:28:36,303
It's screen recording right now so you can see it as I take the car for a drive

356
00:28:36,303 --> 00:28:39,431
to get everything warmed up 
and see what the computer is seeing.

357
00:28:39,431 --> 00:28:43,716
Right now, the engine is stone cold 
and uh well, I'm going to start it.

358
00:28:43,716 --> 00:28:46,069
[engine fires up]

359
00:28:46,069 --> 00:28:49,053
The oxygen sensors should wake up pretty quickly.

360
00:28:49,053 --> 00:28:54,269
But they have to get hot before things 
are really truly right, so, we'll see what happens.

361
00:28:54,269 --> 00:28:59,295
The graph on the bottom 
is showing the voltages from the upstream oxygen sensor.

362
00:28:59,295 --> 00:29:05,259
Remember, this is the one the engine computer is using to make sure its air/fuel calculations are correct.

363
00:29:05,259 --> 00:29:07,797
And we should see oscillation.

364
00:29:07,797 --> 00:29:14,270
It's hard to see the oscillations as it goes slightly rich and slightly lean because the voltage doesn't change much,

365
00:29:14,270 --> 00:29:16,710
but you can make them out a little bit.

366
00:29:16,710 --> 00:29:20,979
The graph on the top is coming from the downstream oxygen sensor...

367
00:29:20,979 --> 00:29:23,384
and this is not good.

368
00:29:23,384 --> 00:29:29,319
It is seeing the same oscillations as the upstream sensor pretty much constantly,

369
00:29:29,319 --> 00:29:34,695
indicating the catalyst isn't 
able to store nearly as much oxygen as it should.

370
00:29:34,695 --> 00:29:39,294
Another thing that is proven here 
is that the oxygen sensors themselves are working.

371
00:29:39,294 --> 00:29:43,824
When, for instance, my foot 
is off the throttle and the car is engine braking,

372
00:29:43,824 --> 00:29:47,173
the downstream sensor voltage drops to near zero.

373
00:29:47,173 --> 00:29:55,044
This is the correct behavior as now the engine is just pumping air and lots of oxygen will make it through to the downstream sensor.

374
00:29:55,044 --> 00:30:01,844
We also see the upstream sensor go high when this happens which for a wideband sensor is normal behavior.

375
00:30:01,844 --> 00:30:07,737
Now if that data is in fact correct then absolutely the cat's bad.

376
00:30:07,737 --> 00:30:12,294
But exhaust leaks can confuse things.

377
00:30:12,294 --> 00:30:19,172
When measuring pure engine exhaust, the oxygen sensors are detecting tiny traces of oxygen.

378
00:30:19,172 --> 00:30:22,908
But the atmosphere has quite a lot of oxygen in it.

379
00:30:22,908 --> 00:30:29,791
And thanks to the fact that the engine sends quick pulses of gas through the exhaust system with each firing cylinder,

380
00:30:29,791 --> 00:30:38,199
there are moments where atmospheric pressure can push a little fresh air into the exhaust system if there are any holes in it.

381
00:30:38,199 --> 00:30:43,211
And if that happens, the oxygen sensors will get false readings.

382
00:30:43,211 --> 00:30:48,096
And this car quite obviously has some significant exhaust leaks.

383
00:30:48,096 --> 00:30:51,124
For one, it's a little loud when the engine is running,

384
00:30:51,124 --> 00:30:54,756
but much more important to diagnosing  a P0420

385
00:30:54,756 --> 00:31:00,005
ever since I've had this car, 
I've been able to smell engine exhaust in the cabin.

386
00:31:00,005 --> 00:31:05,920
The smell comes and goes, but it's most intense 
when pulling in fresh air through the climate vents.

387
00:31:05,920 --> 00:31:09,660
That suggests there's an 
exhaust leak near the engine compartment.

388
00:31:09,660 --> 00:31:14,748
And when sticking my head under the hood 
with the engine running, it's downright stinky.

389
00:31:14,748 --> 00:31:18,572
But what's not stinky is the exhaust coming out the tailpipe.

390
00:31:18,572 --> 00:31:21,596
That is relatively odorless, as it should be,

391
00:31:21,596 --> 00:31:26,501
which suggests that the catalytic converter 
is at least somewhat functional.

392
00:31:26,501 --> 00:31:28,656
Actually, side note,

393
00:31:28,656 --> 00:31:35,374
if you've ever wondered why something like a lawn mower or portable generator smells the way it does when it's running,

394
00:31:35,374 --> 00:31:39,175
that's because they don't have catalytic converters.

395
00:31:39,175 --> 00:31:45,125
Traces of unburnt fuel along with combustion byproducts have 
a very distinctive odor.

396
00:31:45,125 --> 00:31:50,331
And before the catalytic converter came along, 
the world just smelled like that.

397
00:31:50,880 --> 00:31:52,767
All the time.

398
00:31:52,767 --> 00:31:58,461
If a single cylinder engine which you use 
to mow your lawn can make that much of a smell,

399
00:31:58,461 --> 00:32:05,134
imagine what a city full of cars burning much more fuel much more quickly must have smelled like.

400
00:32:05,134 --> 00:32:06,822
It was awful.

401
00:32:06,822 --> 00:32:11,407
And that's before you consider 
that we used to put lead in gasoline!

402
00:32:11,407 --> 00:32:14,926
The catalytic converter is actually the reason leaded gas went away.

403
00:32:14,926 --> 00:32:23,075
If you used leaded gas in a car with a catalytic converter, the lead would contaminate the catalyst and destroy it almost instantly.

404
00:32:23,075 --> 00:32:28,571
It is unquestionably a good thing 
that we require cars to have catalytic converters

405
00:32:28,571 --> 00:32:32,506
and that we require them 
to monitor that they're actually working.

406
00:32:32,506 --> 00:32:36,310
But through neutralizing the smell of burning gasoline,

407
00:32:36,310 --> 00:32:42,685
these really do a fantastic job of 
hiding just how much gasoline we are burning.

408
00:32:42,685 --> 00:32:45,558
The numbers on a gas pump are just numbers.

409
00:32:45,558 --> 00:32:51,958
Unless something's gone horribly wrong, you don't actually see the 10 gallons of fuel you just pumped into your car

410
00:32:51,958 --> 00:32:55,730
and are about to set on fire over the next week or two.

411
00:32:55,730 --> 00:32:58,998
You might get a whiff of the gas when you close the gas cap,

412
00:32:58,998 --> 00:33:01,370
but otherwise it's out of sight,

413
00:33:01,440 --> 00:33:04,726
out of smell, and out of mind.

414
00:33:04,726 --> 00:33:10,110
I've often wondered how much more apparent the environmental harm of our car dependent society would be

415
00:33:10,110 --> 00:33:13,965
if cars still smelled like they did back in the early '70s.

416
00:33:13,965 --> 00:33:19,756
Next time you're behind a classic car, 
pay attention to what it smells like outside.

417
00:33:19,756 --> 00:33:24,541
And then remember, cars all used to smell like that.

418
00:33:24,541 --> 00:33:30,485
And since the Cube kind of does smell like an old car right now, there was only one thing left to do:

419
00:33:30,485 --> 00:33:35,633
inspect the exhaust system for 
signs of a leak near the catalytic converter.

420
00:33:35,633 --> 00:33:40,502
First, I wanted to check the 
exhaust manifold for cracks or a leaking gasket,

421
00:33:40,502 --> 00:33:47,056
but the catalytic converter bolts to the exhaust manifold in such a way that makes it very difficult to see.

422
00:33:47,056 --> 00:33:49,531
So, I had no choice to unbolt it.

423
00:33:49,531 --> 00:33:54,457
And once I did... well, that could be a problem.

424
00:33:54,457 --> 00:34:00,876
There's a ton of carbon buildup around this flange, 
indicating a significant exhaust leak.

425
00:34:00,876 --> 00:34:07,879
And this is exactly where an exhaust leak would be most likely to cause an erroneous P0420.

426
00:34:07,879 --> 00:34:16,415
It's right next to the upstream oxygen sensor, and that could cause the computer to believe the engine is running leaner than it actually is.

427
00:34:16,415 --> 00:34:20,508
That would cause it to chronically run the engine a little too rich,

428
00:34:20,508 --> 00:34:25,077
meaning the catalyst might never 
get enough oxygen to optimally function.

429
00:34:25,077 --> 00:34:30,637
And even if this leak isn't affecting the upstream sensor and the engine is operating normally,

430
00:34:30,637 --> 00:34:37,582
too much air entering the catalyst could tip the scale just enough for the second oxygen sensor to see oscillations

431
00:34:37,582 --> 00:34:41,288
which the computer will interpret as inefficient operation.

432
00:34:41,288 --> 00:34:46,287
So, before I condemn this as bad, I need to fix that leak.

433
00:34:46,287 --> 00:34:51,958
One new flange donut and a set of 
spring bolts later, and I had reinstalled the converter.

434
00:34:51,958 --> 00:34:57,003
I also had to bodge this fix on the rear flange because it was completely falling apart.

435
00:34:57,003 --> 00:35:02,120
I didn't have much confidence that was a good seal, but this is past the second unmonitored catalyst,

436
00:35:02,120 --> 00:35:07,198
so a leak here might be loud, 
but it shouldn't affect the sensor readouts.

437
00:35:07,198 --> 00:35:10,982
And with that repair done, I took it for another test drive.

438
00:35:10,982 --> 00:35:12,190
Good news?

439
00:35:12,190 --> 00:35:14,655
I definitely fixed the exhaust leak.

440
00:35:14,655 --> 00:35:18,602
The smell went away completely, 
both in the car and under the hood.

441
00:35:18,602 --> 00:35:20,418
Bad news?

442
00:35:21,477 --> 00:35:27,253
Well, you see it on the desk right now, and this is what the data looked like.

443
00:35:27,253 --> 00:35:30,382
Yep, almost nothing changed at all.

444
00:35:30,382 --> 00:35:37,267
I could see tiny differences in behavior, 
but the rear oxygen sensor was still switching way too much.

445
00:35:37,267 --> 00:35:44,285
I looked at the fuel trim data to see if the car was making any major adjustments after this repair, and it really wasn't.

446
00:35:44,285 --> 00:35:47,832
These values for short-term fuel trim are well within normal,

447
00:35:47,832 --> 00:35:52,436
so the upstream oxygen sensor was apparently unaffected by the leak.

448
00:35:52,436 --> 00:35:56,209
As a last ditch effort, I used the scan tool to clear the codes

449
00:35:56,209 --> 00:36:04,302
hoping that maybe it had a default strategy with a P0420 set, which wouldn't show a fix in the sensor data...

450
00:36:04,302 --> 00:36:09,393
but after just one test drive, 
the P0420 came back as a pending code.

451
00:36:09,393 --> 00:36:11,521
Meaning that even after clearing the codes,

452
00:36:11,600 --> 00:36:17,252
it took only about 20 minutes for the computer to say, 
"Yeah, this catalytic converter is bad."

453
00:36:17,252 --> 00:36:18,868
So...

454
00:36:18,868 --> 00:36:20,004
[sighs]

455
00:36:20,357 --> 00:36:22,766
[lift starts]

456
00:36:22,923 --> 00:36:28,721
Yes, one very expensive purchase later 
and I had a new catalytic converter.

457
00:36:28,721 --> 00:36:30,678
I took the old one back out of the car,

458
00:36:30,678 --> 00:36:35,635
then swapped the downstream oxygen sensor from the old one to the new one using the wrong wrench

459
00:36:35,635 --> 00:36:37,558
(but is it really wrong if it works?)

460
00:36:37,558 --> 00:36:40,774
and then I could put the new cat in the cube.

461
00:36:40,774 --> 00:36:49,522
And because this "factory fit" aftermarket catalytic converter has weirdly thick flanges, that was quite a struggle!

462
00:36:49,522 --> 00:36:52,750
I really needed longer spring bolts for the manifold.

463
00:36:52,750 --> 00:36:59,128
And then I discovered the flange on the output side had different threading from the factory spring bolts.

464
00:36:59,128 --> 00:37:01,584
Either that or the parts store had the wrong information.

465
00:37:01,584 --> 00:37:04,298
The lesson here is be nice to automotive technicians.

466
00:37:04,298 --> 00:37:06,267
They put up with a lot of crap.

467
00:37:06,267 --> 00:37:09,802
So, did I just make a really expensive mistake?

468
00:37:09,802 --> 00:37:11,830
Only one way to find out.

469
00:37:11,830 --> 00:37:14,239
Let's start this sucker up and see what happens.

470
00:37:14,239 --> 00:37:17,254
[engine cranks over and roars to life]

471
00:37:19,040 --> 00:37:22,211
Well, the good thing is it doesn't sound any 
louder than it used to.

472
00:37:22,211 --> 00:37:24,722
But we got to watch the data and see what we see.

473
00:37:24,722 --> 00:37:27,836
Well, when I took the car for its post repair test drive,

474
00:37:27,836 --> 00:37:34,159
once the rear oxygen sensor woke up 
and started reporting rich, it stayed that way.

475
00:37:34,159 --> 00:37:37,455
The oscillations had completely disappeared.

476
00:37:37,455 --> 00:37:43,051
I want to make sure I call out that this is the same oxygen sensor that was in the car before.

477
00:37:43,051 --> 00:37:49,529
A lot of people go chucking 
oxygen sensors at cars with catalyst codes, hoping that will fix things,

478
00:37:49,529 --> 00:37:51,664
but that rarely ever works.

479
00:37:51,664 --> 00:37:55,180
See, the car has ways to test its oxygen sensors:

480
00:37:55,180 --> 00:38:00,152
checking for voltages that are too high or too low, 
checking whether the heaters are working or not,

481
00:38:00,152 --> 00:38:06,433
and even checking to make sure they switch to reporting lean or rich when expected and quickly enough.

482
00:38:06,433 --> 00:38:16,255
It's pretty unlikely an O2 sensor goes bad without the computer knowing it and setting an O2 sensor code like P0133 or P0139.

483
00:38:16,255 --> 00:38:21,404
While it sure looks like a fix, 
it will take a few drive cycles to know for certain.

484
00:38:21,404 --> 00:38:26,537
You'll notice when I scanned the codes 
earlier that there was a permanent P0420.

485
00:38:26,537 --> 00:38:30,234
This is because once the car 
decides it has a bad catalytic converter,

486
00:38:30,234 --> 00:38:38,406
it flags that trouble code as permanent and it won't go away even if someone uses a scan tool to clear the codes.

487
00:38:38,406 --> 00:38:45,464
This is to prevent people who might try that just to make the engine light go out from fooling an emissions test that easily.

488
00:38:45,464 --> 00:38:49,976
But after enough trips in the car where the performance looks normal to the computer,

489
00:38:49,976 --> 00:38:53,291
the car will clear the permanent code on its own.

490
00:38:53,291 --> 00:38:58,140
And I am happy to report there are now no codes present.

491
00:38:58,140 --> 00:39:03,588
It is admittedly a little concerning 
that the original catalytic converter failed.

492
00:39:03,588 --> 00:39:06,982
They usually don't just stop working one day,

493
00:39:06,982 --> 00:39:13,184
and it could be that in this car's past it had a severe engine misfire or perhaps a stuck fuel injector,

494
00:39:13,184 --> 00:39:16,425
either one of which could have poisoned the catalyst.

495
00:39:16,425 --> 00:39:21,939
Incidentally, if your engine is misfiring, 
the check engine light should be flashing.

496
00:39:21,939 --> 00:39:25,088
Never ignore a flashing check engine light.

497
00:39:25,088 --> 00:39:30,664
This means something is majorly wrong and the catalyst could 
be damaged depending on what's up.

498
00:39:30,664 --> 00:39:34,241
So, don't let a small thing become a big thing.

499
00:39:34,241 --> 00:39:41,782
But this car also has 187,000 miles on it and since it had an exhaust leak for who knows how long,

500
00:39:41,782 --> 00:39:46,909
it could very well simply be 
a combination of age and excess oxygen or something.

501
00:39:46,909 --> 00:39:48,891
Regardless, it's got a new one.

502
00:39:48,891 --> 00:39:51,168
The engine doesn't seem to be burning oil or anything,

503
00:39:51,168 --> 00:39:54,844
and so long as nothing new crops up, it should be good to go.

504
00:39:54,844 --> 00:39:59,027
But I didn't just buy this car to replace its catalytic converter.

505
00:39:59,027 --> 00:40:02,766
Actually, I was very much hoping not to have to do that!

506
00:40:02,766 --> 00:40:06,730
In future videos, we're going to be looking at all the other sensors that are in the car,

507
00:40:06,730 --> 00:40:10,175
including those which aren't in the engine at all.

508
00:40:10,175 --> 00:40:14,879
For instance, do you know why 
a loose gas cap will turn on the check engine light?

509
00:40:14,879 --> 00:40:22,530
Well, that's because the car also has an evaporative emissions system designed to keep gasoline vapors entirely in the tank.

510
00:40:22,530 --> 00:40:26,438
And part of that includes a box filled with charcoal.

511
00:40:26,438 --> 00:40:31,221
There's so much to explore with modern cars, 
even basic ones like this.

512
00:40:31,221 --> 00:40:35,345
From anti-lock brakes to variable valve timing and more.

513
00:40:35,345 --> 00:40:38,797
So, like the computer does for the engine:

514
00:40:38,797 --> 00:40:40,192
stay tuned.

515
00:40:41,212 --> 00:40:43,820
♫ stoichiometrically smooth jazz ♫

516
00:40:44,566 --> 00:40:46,927
...gasoline's volatile nature means it could...

517
00:40:46,927 --> 00:40:50,491
Yeah, I'm starting this over. 
Something weird happened a couple of times. [laughs]

518
00:40:50,491 --> 00:40:53,445
...only handled carbon numo
 [proceeds to make many grunting noises]

519
00:40:53,445 --> 00:40:56,638
...required the engine to be reco - ah, reQUIre

520
00:40:56,638 --> 00:40:59,037
and that's what this is.

521
00:40:59,037 --> 00:41:03,100
As you can see, this thing is installed - don't point to that one!

522
00:41:03,100 --> 00:41:04,180
Adjust the...

523
00:41:04,180 --> 00:41:04,835
Farts!

524
00:41:04,835 --> 00:41:06,755
...minus 10 degrees outside.

525
00:41:06,755 --> 00:41:09,674
There is some really 
[devolves into a belch]

526
00:41:10,223 --> 00:41:14,860
...we need carbon and carbon monoxide to be available.

527
00:41:14,860 --> 00:41:17,329
Wha that... that sounded weird.

528
00:41:17,329 --> 00:41:22,187
We'll take this out now and you'll - you'll never know the difference.

529
00:41:23,991 --> 00:41:26,981
Look at that. Me being a little trickster.

530
00:41:26,981 --> 00:41:29,597
[smarmily]
That was from a different car!

531
00:41:30,656 --> 00:41:34,986
Normally I'd put a gag here, but this time I'm reminding you about the socks!

532
00:41:34,986 --> 00:41:39,162
Two weeks only, 100% of profits go to charity, and best of all you get two of them!

533
00:41:39,162 --> 00:41:42,930
Every month! Two of them!

534
00:41:42,930 --> 00:41:46,337
Links in the description :)