WEBVTT Kind: captions Language: en 00:00:10.080 --> 00:00:14.690 This Nissan Cube has a little yellow light on  its dashboard which says 00:00:14.690 --> 00:00:16.801 "Service Engine Soon." 00:00:16.801 --> 00:00:21.623 That's its version of a check engine light,  which is more formerly known as the MIL 00:00:21.623 --> 00:00:23.033 which stands for mother-in-law— 00:00:23.033 --> 00:00:25.825 I mean, malfunction indicator lamp. 00:00:25.825 --> 00:00:31.205 And as its name implies, that means something's wrong with this car. 00:00:31.205 --> 00:00:32.662 What's wrong? 00:00:32.662 --> 00:00:38.772 Well, a quick check with one of those Bluetooth code scanners revealed its engine computer has stored the dreaded fault code 00:00:38.772 --> 00:00:43.766 P0420, catalyst system efficiency below threshold. 00:00:43.766 --> 00:00:47.754 In other words, this car thinks its catalytic converter isn't working right. 00:00:47.754 --> 00:00:52.085 And because of that, it would fail an emissions test if I were to take it in for one, 00:00:52.085 --> 00:00:55.683 which I'll have to do before  I can renew its registration. 00:00:55.683 --> 00:00:59.943 But what exactly is the catalytic converter? 00:00:59.943 --> 00:01:01.253 What does it do? 00:01:01.253 --> 00:01:04.465 And how can the car tell it's not working right? 00:01:04.779 --> 00:01:06.073 Well... 00:01:08.662 --> 00:01:12.011 [motor and hydraulic pump whining] 00:01:12.717 --> 00:01:14.490 [ratchet wrench sounds] 00:01:20.334 --> 00:01:23.185 ...this is the catalytic converter. 00:01:23.185 --> 00:01:25.152 Why is it here on the desk? 00:01:25.152 --> 00:01:26.376 We'll get to that. 00:01:26.376 --> 00:01:29.006 As you can see, it's actually quite simple. 00:01:29.006 --> 00:01:33.455 It's basically just a section of exhaust pipe which has a couple of expanded sections 00:01:33.455 --> 00:01:36.688 that are filled with a tightly-packed grid of ceramic material. 00:01:36.688 --> 00:01:41.973 And the engine exhaust flows through those grids before it's released to the atmosphere. 00:01:41.973 --> 00:01:48.668 That ceramic material is coated with precious metals: usually platinum, with a bit of rhodium and palladium for garnish. 00:01:48.668 --> 00:01:52.730 Which is why these things are so expensive and often stolen. 00:01:52.730 --> 00:01:58.890 The precious metals form a Catalyst that Converts smog- and acid rain-forming nitrogen oxides 00:01:58.890 --> 00:02:02.030 into plain old nitrogen and carbon dioxide. 00:02:02.030 --> 00:02:08.997 It will also convert any unburnt hydrocarbons from  imperfect combustion into carbon dioxide and water vapor. 00:02:08.997 --> 00:02:14.493 In other words, this thing's job is to make engine exhaust as harmless as possible. 00:02:14.493 --> 00:02:17.478 But it doesn't work on its own. 00:02:17.478 --> 00:02:26.368 In fact, the chemical reactions which occur inside of here rely on a wildly complicated series of sensors, actuators, and feedback loops 00:02:26.368 --> 00:02:31.628 which the car's engine computer is orchestrating on a second by second basis. 00:02:31.628 --> 00:02:35.008 Now, this is a very ordinary car. 00:02:36.851 --> 00:02:38.162 Okay, well, not really. 00:02:38.162 --> 00:02:39.704 It's a Nissan Cube! 00:02:39.704 --> 00:02:46.505 But I mean it's a 15-year-old economy car which has nothing you might call "advanced technology" under the hood. 00:02:46.505 --> 00:02:49.924 In fact, this one even has a manual transmission. 00:02:49.924 --> 00:02:57.829 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 00:02:57.829 --> 00:03:01.975 every time you turn its key, start the engine, and drive it. 00:03:01.975 --> 00:03:10.790 This engine, the Renault-Nissan MR18DE, is the  1.8 L 4-cylinder engine which powers the car and makes it move. 00:03:10.790 --> 00:03:15.495 But the engine itself is  little more than a complicated air compressor. 00:03:15.495 --> 00:03:21.512 This engine cannot do anything without this little computer box running the show. 00:03:21.512 --> 00:03:26.816 This is the engine control module, and it controls... everything! 00:03:26.816 --> 00:03:31.056 From the spark plugs to the fuel injectors — even the throttle! 00:03:31.056 --> 00:03:37.203 This car's gas pedal is just a fancy joystick telling the computer how far you've pressed it down. 00:03:37.203 --> 00:03:41.680 And this has been the normal reality of cars for quite a long time. 00:03:42.240 --> 00:03:46.098 This video is the first in a series on engine  management technology, 00:03:46.098 --> 00:03:51.420 and while we're going to be exploring a lot of things today to understand the catalytic converter, 00:03:51.420 --> 00:03:55.863 I'll only be scratching the surface and there will be much more to come. 00:03:55.863 --> 00:03:58.531 So, first of all... 00:03:58.531 --> 00:04:02.952 is that one of those progress bars that shows up when people do ad reads? 00:04:02.952 --> 00:04:04.466 On this channel? 00:04:04.466 --> 00:04:06.633 I'm gonna have to put my foot down on that. 00:04:06.868 --> 00:04:10.577 Ooh, are those Technology Connections socks? 00:04:10.577 --> 00:04:11.869 Yes, they are! 00:04:11.869 --> 00:04:17.486 That's right, there is now for the first time official TC merch for sale. 00:04:17.486 --> 00:04:20.954 But... this is only sort of an ad read. 00:04:20.954 --> 00:04:25.141 See, I won't be making a scent from the sale of these socks. 00:04:25.141 --> 00:04:28.549 In fact, all of the profit they generate will go to charity. 00:04:28.549 --> 00:04:35.271 If this sounds familiar to some of you, well, that's because it's a collaboration with the Awesome Socks Club and Good Store. 00:04:35.271 --> 00:04:38.391 I've been a member of the Awesome Socks Club since its inception. 00:04:38.391 --> 00:04:42.244 I love silly socks and haven't worn normal socks in years. 00:04:42.244 --> 00:04:45.661 So, when 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00:05:28.093 These are just some of the designs we've cooked up - the rest will be a fun surprise! 00:05:28.093 --> 00:05:31.029 And not only will you get some great socks, 00:05:31.029 --> 00:05:36.963 but you'll be helping Partners in Health fund and operate the Maternal Center of Excellence in Sierra Leone. 00:05:36.963 --> 00:05:41.388 This world-class facility provides exceptional medical care to mothers and children 00:05:41.388 --> 00:05:45.985 in a region with one of the highest maternal mortality rates in the world. 00:05:45.985 --> 00:05:49.689 If some silly socks which help people sound like your cup of tea, 00:05:49.689 --> 00:05:53.171 there will be information in all the places on how to get them. 00:05:53.171 --> 00:05:56.702 Thanks for your attention and now back to the show. 00:05:56.702 --> 00:06:00.937 So first of all, what is the job of this engine? 00:06:00.937 --> 00:06:07.573 Well, very basically, it's to turn a fuel into physical force which we can use to make things happen. 00:06:07.573 --> 00:06:10.193 Like push a car along a road. 00:06:10.193 --> 00:06:16.600 Like most internal combustion engines, this uses pistons traveling up and down cylindrical combustion chambers 00:06:16.600 --> 00:06:22.464 which are attached to a crankshaft to translate their up and down motion into a spinning motion. 00:06:22.464 --> 00:06:28.232 Valves at the top of the combustion chamber open and close in time with the movement of the pistons 00:06:28.232 --> 00:06:34.615 and through filling the chambers with a basically explosive mix of air and fuel as the pistons move downward, 00:06:34.615 --> 00:06:37.963 then compressing that mixture as the pistons move back up 00:06:37.963 --> 00:06:46.371 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 00:06:46.371 --> 00:06:51.546 and thus the chemical energy in the fuel is converted to mechanical energy. 00:06:51.546 --> 00:06:54.951 Now, as far as explaining  the mechanical parts of the engine, 00:06:54.951 --> 00:06:57.498 that's actually as far as I'm going to go today. 00:06:57.498 --> 00:07:04.008 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. 00:07:04.008 --> 00:07:09.870 But for now, I just want to focus on where air goes in and exhaust comes out. 00:07:09.870 --> 00:07:19.514 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. 00:07:19.514 --> 00:07:24.407 Fuel is mixed in by electronic fuel injectors which live underneath the intake manifold 00:07:24.407 --> 00:07:28.540 and spray it into the airstream as the cylinders ingest air. 00:07:28.540 --> 00:07:37.451 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. 00:07:37.451 --> 00:07:40.796 The catalytic converter bolts to the engine right here. 00:07:40.796 --> 00:07:47.649 It needs to be as close to the engine as possible because the catalyst has to be very hot in order to function. 00:07:47.649 --> 00:07:52.367 And we need this to function because of what happens when we burn gasoline. 00:07:52.367 --> 00:07:55.858 Or rather, what never happens quite correctly. 00:07:55.858 --> 00:08:01.247 But before I explain that, have you ever seen what burning a tablespoon of gasoline looks like? 00:08:01.247 --> 00:08:05.836 Neither have I, but I'm an adult with access to tablespoons and gasoline. 00:08:05.836 --> 00:08:07.593 So, I wanted to find out. 00:08:07.593 --> 00:08:09.523 It looks like this! 00:08:09.523 --> 00:08:12.598 And this flame burned for about 3 minutes. 00:08:12.598 --> 00:08:19.184 But you know how long it takes this Nissan Cube to go through a tablespoon of gasoline when driving 60 mph? 00:08:19.184 --> 00:08:21.390 Seven seconds. 00:08:21.390 --> 00:08:24.006 This car gets 30 miles per gallon on the highway, 00:08:24.006 --> 00:08:30.825 which means it burns through gasoline at a rate of 8.53 tablespoons per minute when traveling 60 mph. 00:08:30.825 --> 00:08:34.892 And have you ever seen what burning 8 tablespoons of gasoline looks like? 00:08:34.892 --> 00:08:38.035 Neither have I, but it looks like this! 00:08:38.035 --> 00:08:43.400 This is what's going on inside the engine of this car when you're driving it at highway speeds. 00:08:43.400 --> 00:08:51.045 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, 00:08:51.045 --> 00:08:54.786 it still took about 3 minutes for  all this to burn away. 00:08:54.786 --> 00:09:00.867 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 00:09:00.867 --> 00:09:03.698 and faster than you see here. 00:09:03.698 --> 00:09:08.812 Now imagine millions of cars are doing this all at the same time. 00:09:08.812 --> 00:09:09.603 Yeah. 00:09:09.680 --> 00:09:14.880 All that smoke and crap is why we spend so much  effort making sure the internal combustion engine   00:09:14.880 --> 00:09:18.152 burns gasoline as cleanly as it can. 00:09:18.152 --> 00:09:22.760 And the catalytic converter is a hugely important part of that goal. 00:09:22.760 --> 00:09:27.247 But before this thing even gets involved, we need to play with chemistry. 00:09:27.247 --> 00:09:33.175 The chemical reaction which occurs inside the engine requires oxygen from the air for combustion. 00:09:33.175 --> 00:09:41.273 The oxygen combines with the hydrocarbons which make up the fuel and the result should simply be carbon dioxide and water vapor. 00:09:41.273 --> 00:09:48.617 Now each molecule of fuel requires a certain number of oxygen molecules for combustion to happen completely. 00:09:48.617 --> 00:09:52.932 This is the basis of the air/fuel mixture we feed into the cylinders. 00:09:52.932 --> 00:09:59.537 If you don't have enough oxygen, the fuel won't burn completely and you'll get unburnt fuel in the exhaust, 00:09:59.537 --> 00:10:01.559 which is not good. 00:10:02.108 --> 00:10:10.283 But if you have too much oxygen, the combustion happens at higher temperatures which lead to nitrogen oxides forming. 00:10:10.283 --> 00:10:12.748 And that's also not good. 00:10:12.748 --> 00:10:19.924 Both unburnt fuel and nitrogen oxides contribute to the formation of smog and acid rain in the atmosphere. 00:10:19.924 --> 00:10:27.045 So ideally we want the engine  to have the exact number of oxygen molecules present in its cylinders 00:10:27.045 --> 00:10:30.714 for the quantity of fuel which is about to be burned. 00:10:30.714 --> 00:10:35.718 If we can manage that, we'd have what's called stochiometric combustion. 00:10:35.718 --> 00:10:43.488 Since gasoline is gasoline and air is air, we actually know the air-to-fuel ratio that results in stochiometric combustion. 00:10:43.488 --> 00:10:49.582 For gasoline, it's a 14.7:1 ratio of air to fuel by mass. 00:10:49.582 --> 00:10:55.043 In the old days, we tried our best to achieve that ratio using a carburetor. 00:10:55.043 --> 00:10:58.802 And we still do actually for lots of small engine equipment. 00:10:58.802 --> 00:11:01.358 Carburetors are extremely simple. 00:11:01.358 --> 00:11:06.070 Basically, you're just running air past a tube with some liquid gasoline in it, 00:11:06.070 --> 00:11:09.588 and the venturi effect causes it to join the airstream. 00:11:09.588 --> 00:11:15.632 Then, gasoline's volatile nature means it quickly becomes a vapor on its way into the engine. 00:11:15.632 --> 00:11:23.370 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, 00:11:23.370 --> 00:11:30.930 which is extra useful because then you can control the power an engine produces simply through restricting its air flow. 00:11:30.930 --> 00:11:32.636 That's what the throttle does. 00:11:32.636 --> 00:11:37.972 When it's closed down, less air can get to the engine which, in the case of a carbureted engine, 00:11:37.972 --> 00:11:42.775 also means less fuel is delivered and thus less power is produced. 00:11:42.775 --> 00:11:49.642 And as the throttle opens, the engine gets more air and the carburetor delivers more fuel, which results in more power. 00:11:49.642 --> 00:11:52.773 All with a consistent air-to-fuel ratio. 00:11:52.773 --> 00:11:56.753 But well, the world isn't quite so simple. 00:11:56.753 --> 00:12:02.441 For a start, there are situations such as acceleration where the engine is under a heavy load 00:12:02.441 --> 00:12:07.649 where we actually need a rich fuel mixture to prevent the engine from running too hot. 00:12:07.649 --> 00:12:11.798 And that will let unburnt fuel into the exhaust system. 00:12:11.798 --> 00:12:19.967 But even if we could always run the engine stoichiometrically, combustion inside the cylinders is never perfect. 00:12:19.967 --> 00:12:23.887 The world is too random and  the pistons are moving too fast. 00:12:23.887 --> 00:12:30.311 So even if you know you've got exactly the correct number of fuel molecules to oxygen molecules, 00:12:30.311 --> 00:12:37.834 you're always going to end up with either some unburnt fuel or some nitrogen oxides or potentially both. 00:12:37.920 --> 00:12:42.066 And that's what the catalytic converter is designed to fix. 00:12:42.066 --> 00:12:46.560 By passing the exhaust through this grid of precious metal-coated material, 00:12:46.560 --> 00:12:53.560 nitrogen oxides are reduced to pure nitrogen and unburnt fuel as well as carbon monoxide are oxidized into carbon dioxide. 00:12:53.560 --> 00:13:02.627 When properly operating, the catalytic converter will all but  eliminate harmful pollutants from the engine. 00:13:04.000 --> 00:13:06.351 Except for carbon dioxide, of course... 00:13:06.351 --> 00:13:10.628 but sadly, we're still having trouble convincing some people that's a problem. 00:13:10.628 --> 00:13:17.099 Catalytic converters became  more or less required in cars sold in the US back in 1975, 00:13:17.099 --> 00:13:20.621 but the earliest ones didn't deal with nitrogen oxides. 00:13:20.621 --> 00:13:26.272 Those so-called two-way converters only handled carbon monoxide and  unburnt fuel - 00:13:26.272 --> 00:13:29.269 which was a tremendous help for air pollution! 00:13:29.269 --> 00:13:33.432 But nitrogen oxides still contribute to smog and acid rain. 00:13:33.432 --> 00:13:39.006 So shortly thereafter, we got three-way catalytic converters which is what this is. 00:13:39.006 --> 00:13:45.671 And if you're wondering why we don't talk about acid rain much anymore, these are a big part of why. 00:13:45.671 --> 00:13:50.609 But with these three-way converters, we have a new can of worms. 00:13:50.609 --> 00:13:54.598 You can't just stick one of these in a car and expect it to work. 00:13:54.598 --> 00:14:01.815 The chemical reactions the catalyst promotes require the engine to be hovering around the stoichiometric point. 00:14:01.815 --> 00:14:07.673 "Hovering around," incidentally, is a fine example of foreshadowing. 00:14:07.673 --> 00:14:11.381 Anyway, if the engine is running too rich or too lean, 00:14:11.381 --> 00:14:17.165 not only will the catalyst stop functioning, but if those incorrect conditions go on for too long, 00:14:17.165 --> 00:14:20.094 the catalyst itself can be damaged. 00:14:20.094 --> 00:14:22.588 This sounds like a pretty big problem. 00:14:22.588 --> 00:14:29.839 But, what if we could actually monitor and control the combustion process happening inside the engine in real time? 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. 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. 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 00:14:49.461 --> 00:14:53.830 like computer-controlled carburetors with fresh air injection systems. 00:14:53.830 --> 00:14:59.029 By 1990, we had almost entirely moved on to electronic fuel injection systems 00:14:59.029 --> 00:15:02.294 very similar to the one we find in the Cube. 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. 00:15:07.356 --> 00:15:11.427 Since this car was made after 1996 — 00:15:11.427 --> 00:15:13.802 again, nothing about this is new — 00:15:13.802 --> 00:15:20.137 it has the standard OBDII port under the dashboard which lets scan tools talk to the engine computer. 00:15:20.137 --> 00:15:23.228 OBD stands for onboard diagnostics 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. 00:15:29.120 --> 00:15:31.562 And plenty of other things, too. 00:15:31.562 --> 00:15:36.235 Now, these days, you can pick up a Bluetooth code scanner for about 20 bucks. 00:15:36.235 --> 00:15:40.586 And honestly, if you drive a car, it's probably worth having one of these. 00:15:40.586 --> 00:15:43.719 This scanner, along with the smartphone app you use it with, 00:15:43.719 --> 00:15:47.430 can not only show you what trouble code is causing a check engine light, 00:15:47.430 --> 00:15:54.367 but they can provide enough information to diagnose lots of issues, including the P0420 code the Cube has. 00:15:54.367 --> 00:15:58.548 But for this video series, I wanted something a little more powerful. 00:15:58.548 --> 00:16:02.375 So, I picked up a proper scan tool! 00:16:02.375 --> 00:16:07.015 Which is really just an Android tablet talking to a suspiciously similar Bluetooth dongle... 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 00:16:12.711 --> 00:16:15.500 to hide certain data and functions. 00:16:15.500 --> 00:16:18.534 And I can screen record with it so you can see what I can see! 00:16:18.534 --> 00:16:22.730 For now, I'm just going to use the standard OBDII protocols. 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. 00:16:30.969 --> 00:16:34.214 And once it has its list, we can go through it. 00:16:34.214 --> 00:16:38.186 This is just some of the data the engine computer is collecting. 00:16:38.186 --> 00:16:43.134 But I want to call out this: air flow rate from mass air flow sensor. 00:16:43.134 --> 00:16:47.252 Remember that the cylinders are being fed air from the intake manifold. 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. 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. 00:16:59.279 --> 00:17:04.284 But between the filter housing and the throttle is the mass air flow sensor. 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. 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. 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. 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, 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. 00:17:37.919 --> 00:17:43.175 Once the computer knows how many grams of air are going into the engine per second, 00:17:43.175 --> 00:17:47.167 it can calculate the correct amount of fuel to deliver to the cylinders 00:17:47.167 --> 00:17:51.728 in order to achieve ideal combustion for the current operating conditions. 00:17:51.728 --> 00:17:55.602 And it can meter precisely how much fuel will be injected 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. 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, 00:18:11.462 --> 00:18:15.612 can't tell it if its calculations were actually correct. 00:18:15.612 --> 00:18:20.549 For instance, when the engine is cold, gasoline doesn't vaporize as well. 00:18:20.549 --> 00:18:25.443 And while the computer will use the engine coolant temperature sensor to try and compensate, 00:18:25.520 --> 00:18:28.150 that sensor is only so accurate. 00:18:28.150 --> 00:18:32.798 Plus, gasoline is not chemically identical from tank to tank. 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 00:18:39.794 --> 00:18:42.962 doesn't mean it's going to be correct for the next one. 00:18:42.962 --> 00:18:47.320 To allow the computer to check its homework, we need an oxygen sensor. 00:18:47.712 --> 00:18:49.719 And that's what this is. 00:18:49.719 --> 00:18:53.568 As you can see, this thing is installed in the car's exhaust manifold 00:18:53.568 --> 00:18:58.584 and its sensing probe is exposed to the exhaust gases coming from the engine. 00:18:58.584 --> 00:19:01.191 There are two types of oxygen sensors, 00:19:01.191 --> 00:19:05.562 and the Cube has both of them, which is slightly annoying for the purposes of demonstration, 00:19:05.562 --> 00:19:11.857 but the important thing is these can confirm whether the engine is actually running stoichiometrically. 00:19:11.857 --> 00:19:14.607 The sensors themselves are really interesting. 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- 00:19:20.971 --> 00:19:23.855 sort of like a very strange battery. 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. 00:19:30.971 --> 00:19:36.254 The simpler narrowband sensor outputs a voltage that fluctuates between 0 and 1 volt 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, 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. 00:19:50.307 --> 00:19:54.373 But it can't really do anything but indicate rich or lean. 00:19:54.373 --> 00:19:57.046 The midpoint is too fuzzy. 00:19:57.046 --> 00:20:02.016 This, though, is a wideband oxygen sensor which can be made much more precise. 00:20:02.016 --> 00:20:04.582 But... it's a little more complicated. 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 — 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. 00:20:17.476 --> 00:20:21.905 But the oxygen sensor doesn't start working right away. 00:20:21.905 --> 00:20:26.938 It needs to be very hot in order to correctly measure oxygen concentration. 00:20:26.938 --> 00:20:32.489 That's why each time the engine is started, the computer runs in open loop control. 00:20:32.489 --> 00:20:36.001 But once the oxygen sensor is hot enough and it starts responding, 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, 00:20:42.152 --> 00:20:45.897 the computer can switch to closed loop control. 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, 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. 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. 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. 00:21:13.109 --> 00:21:19.822 And by the way, if this sounds complicated - yeah, it is! 00:21:19.822 --> 00:21:23.329 The conditions the engine will see are constantly different. 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, 00:21:29.067 --> 00:21:32.760 increasing engine RPM and the total load. 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. 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 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. 00:21:56.625 --> 00:22:01.529 This allows the engine to have a very nuanced open loop control profile 00:22:01.529 --> 00:22:06.638 which keeps the engine in check  even if one day the oxygen sensor were to fail. 00:22:06.638 --> 00:22:10.544 Though of course the computer can detect an issue with the oxygen sensor 00:22:10.544 --> 00:22:15.530 and will set a fault code which turns on the check engine light if that happens. 00:22:15.530 --> 00:22:19.750 But the oxygen sensor itself is also used to detect other issues. 00:22:19.750 --> 00:22:25.502 Say for instance one day the oxygen sensor sees a very different oxygen concentration 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. 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. 00:22:39.594 --> 00:22:41.447 But speaking of fault codes, 00:22:41.447 --> 00:22:45.455 the only code that's in this car is P0420. 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... 00:22:50.809 --> 00:22:52.856 in fact, any of the sensors. 00:22:52.856 --> 00:22:57.368 but it does think this catalytic converter ain't working. 00:22:57.368 --> 00:22:59.993 How can it be so sure of that? 00:22:59.993 --> 00:23:05.488 Well, the catalytic converter is being monitored by a second oxygen sensor. 00:23:05.488 --> 00:23:06.938 That one. 00:23:06.938 --> 00:23:13.053 By measuring the oxygen  concentration in the exhaust after it has passed through the catalytic converter, 00:23:13.053 --> 00:23:18.577 the computer can determine how much converting is catalactually happening. 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. 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. 00:23:31.278 --> 00:23:37.454 Notice that in order to oxidize any unburnt fuel, we need oxygen available to the catalyst. 00:23:37.454 --> 00:23:41.361 Sounds easy. Just run the engine a little bit lean, right? 00:23:41.361 --> 00:23:43.500 Well, we could. 00:23:43.500 --> 00:23:48.276 But notice that in order for the nitrogen oxides to be reduced to nitrogen, 00:23:48.276 --> 00:23:52.238 we need carbon and carbon monoxide to be available. 00:23:52.238 --> 00:23:57.176 Which only happens when the fuel mixture is a little bit rich. 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. 00:24:02.127 --> 00:24:07.544 This feels like a catch 22, so... how is this supposed to work? 00:24:07.544 --> 00:24:12.909 Well, the engine computer isn't actually trying for perfect combustion. 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. 00:24:21.055 --> 00:24:23.911 It needs to be close to stochiometric combustion, 00:24:23.911 --> 00:24:29.844 but for the catalytic converter to promote both reactions, it can't stay there. 00:24:29.844 --> 00:24:35.098 The teeter tottering it does means that when the engine is running a little lean, 00:24:35.098 --> 00:24:41.778 there are free oxygen molecules in the exhaust which the catalyst will absorb and hold onto. 00:24:41.778 --> 00:24:46.313 Then when the engine computer switches back to a slightly rich mixture, 00:24:46.313 --> 00:24:50.060 we get the inputs we need to reduce  nitrogen oxides. 00:24:50.060 --> 00:24:56.566 And the stored oxygen in the catalyst will then oxidize whatever excess unburnt fuel remains 00:24:56.566 --> 00:25:00.815 after the nitrogen oxide reduction reactions are complete. 00:25:00.815 --> 00:25:05.567 We can actually observe  the engine computer causing these oscillations. 00:25:05.567 --> 00:25:08.288 At least... sort of. 00:25:08.288 --> 00:25:12.582 This is why the Cube's wideband sensor is a little annoying. 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. 00:25:20.354 --> 00:25:24.022 An equivalence ratio of one would be stochiometric. 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. 00:25:28.759 --> 00:25:32.451 It keeps going a little high then a little low. 00:25:32.451 --> 00:25:34.719 But this is just data from the oxygen sensor. 00:25:34.719 --> 00:25:39.637 Here we can see the equivalence ratio the computer is actually trying for. 00:25:39.637 --> 00:25:43.219 And as you can see, it's not shooting for one. 00:25:43.219 --> 00:25:45.520 It's constantly going back and forth. 00:25:45.520 --> 00:25:48.071 First lean to charge the catalyst with oxygen, 00:25:48.071 --> 00:25:51.928 then rich to provide the inputs needed to reduce nitrogen oxides, 00:25:51.928 --> 00:25:55.664 and then back to lean to  get more oxygen to the catalyst. 00:25:55.664 --> 00:26:01.616 Incidentally, if you've ever heard that catalytic converters get very hot, this is why. 00:26:01.616 --> 00:26:05.554 Unburnt fuel still has energy in it, and when the engine is running rich 00:26:05.554 --> 00:26:10.982 the oxidation reactions which take place inside the catalytic converter release that energy. 00:26:10.982 --> 00:26:13.488 So it gets real toasty in there. 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? 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, 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, 00:26:34.027 --> 00:26:41.616 if the catalyst is actually functioning, very little detectable oxygen should make it to this sensor. 00:26:41.616 --> 00:26:45.918 It should be used up before the exhaust makes it to this point. 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. 00:26:54.863 --> 00:27:00.138 It should always see what looks like rich conditions without any oxygen. 00:27:00.138 --> 00:27:03.094 If this can detect the engine computer's oscillations, 00:27:03.094 --> 00:27:09.498 that means the oxidation reactions which should be happening in the catalyst are no longer occurring. 00:27:09.498 --> 00:27:13.939 Or, at least, they're not occurring as completely as they should. 00:27:13.939 --> 00:27:21.082 This indicates the catalyst is losing oxygen storage capacity and thus has lost efficiency. 00:27:21.082 --> 00:27:25.653 And that is why this car has a P0420 trouble code. 00:27:25.653 --> 00:27:30.249 This downstream oxygen sensor is able to see too much oscillation, 00:27:30.249 --> 00:27:33.194 which indicates the catalyst isn't working. 00:27:33.194 --> 00:27:36.923 Now, some detected oscillation is okay. 00:27:36.923 --> 00:27:40.483 If you remember that the trouble code said "below threshold," 00:27:40.560 --> 00:27:44.760 that's because the logic in the engine computer is a little lenient. 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. 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. 00:27:58.574 --> 00:28:02.157 And that process isn't necessarily going to work on the first try. 00:28:02.157 --> 00:28:04.914 The computer's not in control of this thing. 00:28:04.914 --> 00:28:10.000 So, the downstream sensor  may mirror the upstream sensor for a short time. 00:28:10.640 --> 00:28:14.244 This is a long way of saying that before I  condemn the catalytic converter, 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. 00:28:20.504 --> 00:28:23.823 So, I need to take it for a test drive. 00:28:23.823 --> 00:28:25.372 Okay, so here's what's going on: 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. 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 00:28:36.303 --> 00:28:39.431 to get everything warmed up and see what the computer is seeing. 00:28:39.431 --> 00:28:43.716 Right now, the engine is stone cold and uh well, I'm going to start it. 00:28:43.716 --> 00:28:46.069 [engine fires up] 00:28:46.069 --> 00:28:49.053 The oxygen sensors should wake up pretty quickly. 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. 00:28:54.269 --> 00:28:59.295 The graph on the bottom is showing the voltages from the upstream oxygen sensor. 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. 00:29:05.259 --> 00:29:07.797 And we should see oscillation. 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, 00:29:14.270 --> 00:29:16.710 but you can make them out a little bit. 00:29:16.710 --> 00:29:20.979 The graph on the top is coming from the downstream oxygen sensor... 00:29:20.979 --> 00:29:23.384 and this is not good. 00:29:23.384 --> 00:29:29.319 It is seeing the same oscillations as the upstream sensor pretty much constantly, 00:29:29.319 --> 00:29:34.695 indicating the catalyst isn't able to store nearly as much oxygen as it should. 00:29:34.695 --> 00:29:39.294 Another thing that is proven here is that the oxygen sensors themselves are working. 00:29:39.294 --> 00:29:43.824 When, for instance, my foot  is off the throttle and the car is engine braking, 00:29:43.824 --> 00:29:47.173 the downstream sensor voltage drops to near zero. 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. 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. 00:30:01.844 --> 00:30:07.737 Now if that data is in fact correct then absolutely the cat's bad. 00:30:07.737 --> 00:30:12.294 But exhaust leaks can confuse things. 00:30:12.294 --> 00:30:19.172 When measuring pure engine exhaust, the oxygen sensors are detecting tiny traces of oxygen. 00:30:19.172 --> 00:30:22.908 But the atmosphere has quite a lot of oxygen in it. 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, 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. 00:30:38.199 --> 00:30:43.211 And if that happens, the oxygen sensors will get false readings. 00:30:43.211 --> 00:30:48.096 And this car quite obviously has some significant exhaust leaks. 00:30:48.096 --> 00:30:51.124 For one, it's a little loud when the engine is running, 00:30:51.124 --> 00:30:54.756 but much more important to diagnosing a P0420 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. 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. 00:31:05.920 --> 00:31:09.660 That suggests there's an exhaust leak near the engine compartment. 00:31:09.660 --> 00:31:14.748 And when sticking my head under the hood with the engine running, it's downright stinky. 00:31:14.748 --> 00:31:18.572 But what's not stinky is the exhaust coming out the tailpipe. 00:31:18.572 --> 00:31:21.596 That is relatively odorless, as it should be, 00:31:21.596 --> 00:31:26.501 which suggests that the catalytic converter is at least somewhat functional. 00:31:26.501 --> 00:31:28.656 Actually, side note, 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, 00:31:35.374 --> 00:31:39.175 that's because they don't have catalytic converters. 00:31:39.175 --> 00:31:45.125 Traces of unburnt fuel along with combustion byproducts have  a very distinctive odor. 00:31:45.125 --> 00:31:50.331 And before the catalytic converter came along, the world just smelled like that. 00:31:50.880 --> 00:31:52.767 All the time. 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, 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. 00:32:05.134 --> 00:32:06.822 It was awful. 00:32:06.822 --> 00:32:11.407 And that's before you consider that we used to put lead in gasoline! 00:32:11.407 --> 00:32:14.926 The catalytic converter is actually the reason leaded gas went away. 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. 00:32:23.075 --> 00:32:28.571 It is unquestionably a good thing that we require cars to have catalytic converters 00:32:28.571 --> 00:32:32.506 and that we require them to monitor that they're actually working. 00:32:32.506 --> 00:32:36.310 But through neutralizing the smell of burning gasoline, 00:32:36.310 --> 00:32:42.685 these really do a fantastic job of hiding just how much gasoline we are burning. 00:32:42.685 --> 00:32:45.558 The numbers on a gas pump are just numbers. 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 00:32:51.958 --> 00:32:55.730 and are about to set on fire over the next week or two. 00:32:55.730 --> 00:32:58.998 You might get a whiff of the gas when you close the gas cap, 00:32:58.998 --> 00:33:01.370 but otherwise it's out of sight, 00:33:01.440 --> 00:33:04.726 out of smell, and out of mind. 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 00:33:10.110 --> 00:33:13.965 if cars still smelled like they did back in the early '70s. 00:33:13.965 --> 00:33:19.756 Next time you're behind a classic car, pay attention to what it smells like outside. 00:33:19.756 --> 00:33:24.541 And then remember, cars all used to smell like that. 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: 00:33:30.485 --> 00:33:35.633 inspect the exhaust system for signs of a leak near the catalytic converter. 00:33:35.633 --> 00:33:40.502 First, I wanted to check the  exhaust manifold for cracks or a leaking gasket, 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. 00:33:47.056 --> 00:33:49.531 So, I had no choice to unbolt it. 00:33:49.531 --> 00:33:54.457 And once I did... well, that could be a problem. 00:33:54.457 --> 00:34:00.876 There's a ton of carbon buildup around this flange, indicating a significant exhaust leak. 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. 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. 00:34:16.415 --> 00:34:20.508 That would cause it to chronically run the engine a little too rich, 00:34:20.508 --> 00:34:25.077 meaning the catalyst might never  get enough oxygen to optimally function. 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, 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 00:34:37.582 --> 00:34:41.288 which the computer will interpret as inefficient operation. 00:34:41.288 --> 00:34:46.287 So, before I condemn this as bad, I need to fix that leak. 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. 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. 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, 00:35:02.120 --> 00:35:07.198 so a leak here might be loud, but it shouldn't affect the sensor readouts. 00:35:07.198 --> 00:35:10.982 And with that repair done, I took it for another test drive. 00:35:10.982 --> 00:35:12.190 Good news? 00:35:12.190 --> 00:35:14.655 I definitely fixed the exhaust leak. 00:35:14.655 --> 00:35:18.602 The smell went away completely, both in the car and under the hood. 00:35:18.602 --> 00:35:20.418 Bad news? 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. 00:35:27.253 --> 00:35:30.382 Yep, almost nothing changed at all. 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. 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. 00:35:44.285 --> 00:35:47.832 These values for short-term fuel trim are well within normal, 00:35:47.832 --> 00:35:52.436 so the upstream oxygen sensor was apparently unaffected by the leak. 00:35:52.436 --> 00:35:56.209 As a last ditch effort, I used the scan tool to clear the codes 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... 00:36:04.302 --> 00:36:09.393 but after just one test drive, the P0420 came back as a pending code. 00:36:09.393 --> 00:36:11.521 Meaning that even after clearing the codes, 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." 00:36:17.252 --> 00:36:18.868 So... 00:36:18.868 --> 00:36:20.004 [sighs] 00:36:20.357 --> 00:36:22.766 [lift starts] 00:36:22.923 --> 00:36:28.721 Yes, one very expensive purchase later and I had a new catalytic converter. 00:36:28.721 --> 00:36:30.678 I took the old one back out of the car, 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 00:36:35.635 --> 00:36:37.558 (but is it really wrong if it works?) 00:36:37.558 --> 00:36:40.774 and then I could put the new cat in the cube. 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! 00:36:49.522 --> 00:36:52.750 I really needed longer spring bolts for the manifold. 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. 00:36:59.128 --> 00:37:01.584 Either that or the parts store had the wrong information. 00:37:01.584 --> 00:37:04.298 The lesson here is be nice to automotive technicians. 00:37:04.298 --> 00:37:06.267 They put up with a lot of crap. 00:37:06.267 --> 00:37:09.802 So, did I just make a really expensive mistake? 00:37:09.802 --> 00:37:11.830 Only one way to find out. 00:37:11.830 --> 00:37:14.239 Let's start this sucker up and see what happens. 00:37:14.239 --> 00:37:17.254 [engine cranks over and roars to life] 00:37:19.040 --> 00:37:22.211 Well, the good thing is it doesn't sound any  louder than it used to. 00:37:22.211 --> 00:37:24.722 But we got to watch the data and see what we see. 00:37:24.722 --> 00:37:27.836 Well, when I took the car for its post repair test drive, 00:37:27.836 --> 00:37:34.159 once the rear oxygen sensor woke up and started reporting rich, it stayed that way. 00:37:34.159 --> 00:37:37.455 The oscillations had completely disappeared. 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. 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, 00:37:49.529 --> 00:37:51.664 but that rarely ever works. 00:37:51.664 --> 00:37:55.180 See, the car has ways to test its oxygen sensors: 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, 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. 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. 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. 00:38:21.404 --> 00:38:26.537 You'll notice when I scanned the codes earlier that there was a permanent P0420. 00:38:26.537 --> 00:38:30.234 This is because once the car decides it has a bad catalytic converter, 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. 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. 00:38:45.464 --> 00:38:49.976 But after enough trips in the car where the performance looks normal to the computer, 00:38:49.976 --> 00:38:53.291 the car will clear the permanent code on its own. 00:38:53.291 --> 00:38:58.140 And I am happy to report there are now no codes present. 00:38:58.140 --> 00:39:03.588 It is admittedly a little concerning that the original catalytic converter failed. 00:39:03.588 --> 00:39:06.982 They usually don't just stop working one day, 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, 00:39:13.184 --> 00:39:16.425 either one of which could have poisoned the catalyst. 00:39:16.425 --> 00:39:21.939 Incidentally, if your engine is misfiring, the check engine light should be flashing. 00:39:21.939 --> 00:39:25.088 Never ignore a flashing check engine light. 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. 00:39:30.664 --> 00:39:34.241 So, don't let a small thing become a big thing. 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, 00:39:41.782 --> 00:39:46.909 it could very well simply be a combination of age and excess oxygen or something. 00:39:46.909 --> 00:39:48.891 Regardless, it's got a new one. 00:39:48.891 --> 00:39:51.168 The engine doesn't seem to be burning oil or anything, 00:39:51.168 --> 00:39:54.844 and so long as nothing new crops up, it should be good to go. 00:39:54.844 --> 00:39:59.027 But I didn't just buy this car to replace its catalytic converter. 00:39:59.027 --> 00:40:02.766 Actually, I was very much hoping not to have to do that! 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, 00:40:06.730 --> 00:40:10.175 including those which aren't in the engine at all. 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? 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. 00:40:22.530 --> 00:40:26.438 And part of that includes a box filled with charcoal. 00:40:26.438 --> 00:40:31.221 There's so much to explore with modern cars,  even basic ones like this. 00:40:31.221 --> 00:40:35.345 From anti-lock brakes to variable valve timing and more. 00:40:35.345 --> 00:40:38.797 So, like the computer does for the engine: 00:40:38.797 --> 00:40:40.192 stay tuned. 00:40:41.212 --> 00:40:43.820 ♫ stoichiometrically smooth jazz ♫ 00:40:44.566 --> 00:40:46.927 ...gasoline's volatile nature means it could... 00:40:46.927 --> 00:40:50.491 Yeah, I'm starting this over. Something weird happened a couple of times. [laughs] 00:40:50.491 --> 00:40:53.445 ...only handled carbon numo [proceeds to make many grunting noises] 00:40:53.445 --> 00:40:56.638 ...required the engine to be reco - ah, reQUIre 00:40:56.638 --> 00:40:59.037 and that's what this is. 00:40:59.037 --> 00:41:03.100 As you can see, this thing is installed - don't point to that one! 00:41:03.100 --> 00:41:04.180 Adjust the... 00:41:04.180 --> 00:41:04.835 Farts! 00:41:04.835 --> 00:41:06.755 ...minus 10 degrees outside. 00:41:06.755 --> 00:41:09.674 There is some really [devolves into a belch] 00:41:10.223 --> 00:41:14.860 ...we need carbon and carbon monoxide to be available. 00:41:14.860 --> 00:41:17.329 Wha that... that sounded weird. 00:41:17.329 --> 00:41:22.187 We'll take this out now and you'll - you'll never know the difference. 00:41:23.991 --> 00:41:26.981 Look at that. Me being a little trickster. 00:41:26.981 --> 00:41:29.597 [smarmily] That was from a different car! 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! 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! 00:41:39.162 --> 00:41:42.930 Every month! Two of them! 00:41:42.930 --> 00:41:46.337 Links in the description :)