Car Corner: Sensors 2010

hi my name is Richard Saxton I'm the coordinator of the automotive technology program at the Community College of Philadelphia in today's episode of car corner you're going to see mr. Dan Reid explain what's behind that mysterious check engine light if you have any other questions about the automotive technology program please contact us at the website hi I'm Dan Reeves the Community College of Philadelphia welcome to car corner today we're going to be talking about automotive sensors' and tools to use to diagnose them and first you have to understand that sensors are necessary if you think about the human body and our own sensory inputs sight taste touch smell hearing those are all inputs and they're what we use to navigate the world around us car sensors work the same way they just don't necessarily see and touch the same things that we do they work a little bit differently and when there's a problem sometimes it can be a big repair fairly costly or sometimes it can be a fairly simple easy repair and sometimes just like the human body your brain may be telling you something is wrong but the fact is is there's actually a problem with something else and it may not even be a major issue so first let's take a look at some of the basic tools that we're going to use to take a look at some of the automotive sensors' and cars today the first and most basic tool is over here this is a digital multimeter and the digital multimeter is basically a tool that just measures different types of electricity car sensors work on electricity they take physical information and transfer it into electrical signals and then send that to a central computer and the separate computer figures out what to do with it just like the human brain the next step up is a debt is a scan tool and the scan tool is a handheld portable computer that's dedicated just to basically talk to the cars automotive electrical systems and sensors if the scan tool detects a problem it's going to basically convert that electrical signal from the car into English or any other language the technician can understand and from there the technician is going to go through and prepare the vehicle a lot of people think that the computer the scan tool that the technician uses is what actually fixes the car and the fact is is it doesn't do that at all the scan tool just informs the technician as to what the problem is and if the sensor is working or not and then from there the technician has to figure out what the actual fault is and I'll show you how this Tool Works in a little bit the next tool that we have and the evolution of scan tools is really just a plain old laptop and what manufacturers realized is that every couple of years or so they would have to come up with a new type of scan tool because the electronics got more complex in the cars what they realized is that if they just used a laptop they could just upgrade the software on a laptop just like there would be an upgrade for an operating system or something to fix a computer bug and what they do is they use a special interface cable to actually connect the laptop to the car and from there the computer can go through and basically act as the scan tool a couple disadvantages to the laptop one it's a laptop it's just a regular computer so it's not real ruggedized for the shop environment and there are models that are made for that and they're pretty costly the other thing is is that this you know portable scan tool this is real easy to take with me in the car and maybe have somebody sit in the passenger seat and look at the sensor data while I'm going down the road and it's just a little easier to control it and you know it has like a video game style setup for the control panel here as opposed to having to punch a bunch of buttons one of the last pieces which is really important and you cannot fix the car without it this is the service manual for the vehicle that we're going to be using today and you can see it's fairly thick okay and what you may think about this is boy there's a lot of information in this book and the fact is there is a lot of information in fact this is pretty much everything there is to know about the car as a whole not just the sensors but if you don't have the information and you don't have the tools you really can't even start to fix a modern car today if there's a sensor problem the way most people know that there's a sensor problem with their cars because the check engine light comes on on the dashboard and when cars first started having check engine lights federally mandated starting in the 1996 model year the light would come on and people would go out and check the oil and the oil would be okay and they would just keep driving the car but the fact is is if that light comes on there's a problem the computers detected a fault and basically I like to call that the money light and not because it costs a lot of money to fix it but the fact is if that light is on your car is either polluting or wasting gas and it's costing you more money okay check engine light is a universal symbol on all vehicle dashboards that either says the words check engine or has a picture of a engine symbol with a little lightning bolt and it may say the words check underneath it there's other warning lights on the dashboard there's a battery light and an oil can light or an oil pressure light and these lights do not mean the same thing as the check engine light a lot of people make that mistake there's also maybe another light known as a maintenance required light which is not the same thing as a check engine light that's from the manufacturer telling you that it's time to get the oil change or time to change an air filter and that's generally set by mileage now the check engine light comes on while you're driving as long as the car is operating properly you can still safely drive that car just make sure that as soon as you can you get it looked at because if the light stays on for too long it's going to end up costing you money the only time that you really have to be concerned about it is if the check engine light is flashing on and off if the check engine light is flashing on and off about once per second while you're driving stop driving the car that light is flashing for a reason it's designed to get your attention it's designed to scare you a little bit but the fact is is if you're driving and that light is flashing you're actually damaging expensive parts of the car typically the catalytic converter or other Michigan system components that can be extremely costly to repair so just pay attention to the check engine light so what we're going to look at next is we're going to look at some of the history involved with the actual sensors and how we moved from where we used to have cars with carburetors to where we are today okay so now we've got some items set up here going through the history a little bit a very abbreviated history of automotive technology and a lot of people you know they they you know think they know the names of car parts and one car part that most people are familiar with even still today is something called a carburetor and this is this is a carburetor alright this is an older what was known as a two-barrel carburetor it had two holes for the air & fuel mixture to go through and carburetors were on vehicles gas powered vehicles and they still are on some gas powered vehicles for almost since the beginning of time and what a carburetor does is it takes in a mixture of air air comes in through the top and then there's this area right here which is called the fuel bowl and down on the inside here of the carburetor are two little feed horns and the fuel would sit in this bowl and get sucked through those feed horns and as you stepped on the gas you would open up a set of throttle plates and allow that air & fuel mixture to get sucked down into the engine where it would be burned and on the surface carburetors are really simple elegant idea I mean you can see that there's there isn't a single wire on this carburetor to make it work it's purely mechanical which was good when we didn't have electronics but the trade-off is and the big problem with carburetors was that when you rebuilt a carburetor carburetor or got a new one it was it was brand it was like a brand-new mechanical clock and everything in it would work perfectly and there were people like my grandfather's that could rebuild these things in 15 minutes with sighs closed but the problem is is once you put them on the car and you got them tuned from that point on their performance started to a degrade a little bit and eventually they would get to the point where they would run so poorly and they would pollute so much and they would waste so much fuel that really wasn't good for the environment or the customer but the problem is is the car still actually ran and it didn't give in an indication on the dashboard that there was a problem so customers would be driving around with poorly performing carburetors for a long time then they would have to get a tune-up get the carburetor rebuilt and you know at one point in time it was not uncommon to rebuild these you know every 15,000 miles we think about a modern car today you're going to get maybe two oil changes in that time two oil changes if you had to rebuild a major part on your car every two oil changes you wouldn't be very happy so it's something to be said about carburetors they work a little bit like a toilet some people kind of get offended at that but the fact is is that's how they work fuel gas comes in through this part here which is a fuel filter and it travels inside this bowl inside this bowl there's a float on a lever so it's like the the tank float inside the toilet and when you step on the gas basically you tell that float to to allow more gas to flow through the carburetor and it's like flushing the toilet handle the gas and you know in this case the water and the waste goes down into the engine and pretty much that's how they worked how they were designed to work later on this is a later carburetor on an intake manifold you can see it's a bit more complex it does start to have some wires and some tubes attached to it and this was because the federal government really started to get strict with carburetors and they said look you know to the manufacturers you got to clean up your act here these things are they're polluting too much and carburetors became incredibly complex I mean they went from simple mechanical units to overly complex mechanical units and a matter of just five years and eventually we did away with them okay we moved on to electronic fuel injection now electronic fuel injection really was pioneered in the 60s and started to become popular in automobiles in the 70s and even more popular in the 80s and generally by the 90s it was in everything that we drove the trade-off is that well we get consistent reliability the car starts every time it doesn't pollute all the time it runs fairly well all the time the trade-off is is the parts are expensive when they fail so what these are is this is what two automotive computers look like if you think about what a household computer looks like it looks very different there is a connector port in the front for wires to go to and the processor itself basically is just like the box of a home computer it takes input signals like a mouse or keyboard would for a home computer and then doesn't output it puts you know letters the internet whatever up on the screen or a printer that's the output so the automotive computer takes a sensors input this guy actually happens to measure air flow the coming into the engine it would send a signal through wires to the computer the computer then would process that signal and then take that wire take that signal through a wire and then control an output and our primary output on our cars computer are the fuel injectors and these guys are just little electronic squirt guns that instead of having a mechanical carburetor control our fuel mixture we just send a little pulse of electricity through a pressurized fuel rail and it sprays an exact amount of fuel into each cylinder as it's needed so it's a much more precise way to deliver fuel to the car as opposed to the carburetor which worked but like I said it would wear out the advantage to this is there's no moving parts there isn't a single moving part in here there's no moving parts in this there's no moving parts in the computer and while the fuel injectors each one has one moving part that's just a little pintle that goes up and down so it's a very reliable system from that standpoint okay what we're going to take a look at when we come back is the individual sensors and what they do on the car and what can happen when they fail okay so now we've got some basic parts set up here and what we're going to look at first is the air that comes into the engine now the air is going to enter through the vehicle's air box and then come through an air filter where then it's going to get pulled through a throttle okay and this is a typical throttle assembly right here this guy you know when you step on the gas it opens up throttle plates and just like our mechanical carburetor this allows a flow of air to come into the vehicle now one of the things is is that with modern fuel injection is the vehicle has to know exactly how much air actually came into the vehicle when you step on the gas you're really stepping on the air and there's two key sensors that are going to tell the vehicle exactly what you want to do I mean that's one of the main inputs to the vehicle is stepping on the gas saying I want to go so the first and most basic type of air flow sensor that we have is this guy and this is called a vane air sensor and this is we use these for about 10 years when fuel injection first came out with some manufacturers and there's just a little flapper door that opens and as you step on the gas the suction from the engine on the intake manifold would actually move this door open and what we have on top here that I have taken away is a small we see that there's a small sensor wire that would move when that flapper door was open so it would change a resistance it would change an electrical signal that would get sent to the cars computer that would say hey you know what right now the driver doesn't have on the gas and right now the driver has the foot all the way on the gas we have a lot of air coming into the engine so if we have a lot of air coming into the engine we need to deliver more fuel and pretty much that's at what fuel injection does is it measures that air and then calculates exactly how much fuel the car needs but you know there's a problem with this it's a moving part okay and moving parts are failure points these things they would get a little bit of moisture in them and in the winter they would freeze and they of course they would freeze shut you go to start your car and it wouldn't work okay unit was very expensive these things from the dealer were probably you know on the upside of 400 bucks and a lot of them probably got replaced unnecessarily because people just didn't understand how it worked or what it did so what we won't moved on to next was we moved on to these two designs and these are called mass airflow sensors and what these do is these have no moving parts but the air moves through this filtered screen and the screen doesn't act like an air filter what it does is it actually straightens the air flow out we want the airflow to go straight across and then what we have here is a little teeny tiny sensor and this little sensor would detect how much air was moving through this tube and based on that it could do a calculation with the computer and it would figure out exactly how much fuel again we needed to deliver so basically it did the same thing that this guy did but it did it with no moving parts so when it comes to cleaning these there's a lot of misconceptions out there about can they be cleaned are you supposed to clean them the fact is is recently on the market there is a product used for cleaning mass airflow sensors in the past what I've seen some people use is something like brake clean which is okay for most plastics but the fact is is it'll actually damage the delicate sensor wire on the mass airflow sensor and the the absolute last thing you ever want to use to clean a car that's fuel-injected is a is a carburetor cleaner type product like this product called gum cutter and you really don't want to use that for cleaning a fuel-injected vehicle this stuff is fine for metals but it really it literally disintegrates plastics and we have too many plastic components and with our sensors today to safely use this so what we have to clean mass airflow sensors is a proper product called mass airflow sensor cleaner and what happens over time is the little sensor wire on the inside here while it's supposed to be self-cleaning it ends up with a little bit of dirt a little bit of oil from the intake and it starts to degrade the performance of the sensor and by spraying this cleaning product which really is is just doesn't leave any residue behind and is safe for plastics it really does a nice job on cleaning the sensor and keeping these guys in check now if a sensor you know if a mass airflow sensor had failed and it came into the shop I might try cleaning it to see if the car runs any better and at that point I might leave it up to the customer as to whether or not they just want to go with the clean sensor or if they want to go ahead and replace it if it made a good enough difference ok the last thing that we have is again with our throttle plate here there's two sensors that are often found on throttle plates and just like our mass airflow sensor to tell the computer exactly how much air enters the engine there's another key sensor called a throttle position sensor that's on the opposite side of the cross shaft from the throttle so I want to open and close the throttle like that it actually moves a little lever on this black sensor right here and there's three teeny tiny wires on the inside there that are going to send a signal back to the computer and this is really what tells the computer exactly what you want to do okay this along with the amount of air coming into the engine the car can really calculate pretty well the exact amount of fuel that it should deliver based on your demand there's one other sensor that sometimes found on the throttle bodies and this little teeny tiny guy right here is called a map sensor ok the map sensor is different than a map sensor the MAF sensor stands for mass airflow map stands for manifold absolute pressure this guy actually measures the pressure inside the intake manifold when the throttle is open and closed if you remember back to physics class when we have pressure drop on an object its temperature changes and that pressure change is able to be measured when we open the throttle it's going to drop and our pressure inside the intake is going to change a little bit so this guy is sometimes found typically a vehicle either has a map or a math it doesn't have them both so your vehicle may have one or the other okay so there's one other thing that we can do with our throttle bodies and that is we can also clean them now you might think it might be a good idea to use the same cleaner I used to clean the mass airflow sensor but the fact is there's one other cleaner that I can use and let me go get it and that's this stuff right here this is air intake cleaner and it comes with a little red straw on the tube and I can spray this inside the throttle body once the car is often it's cool and it can basically wipe the inside of the throttle plates with a rag sometimes actually like to crack this open a little bit spray just a small amount in here wipe it out with a rag sometimes we'll even take an old toothbrush which I would obviously never use again and scrub the inside of this out and then wipe it out with the rag and what happens is on the inside here is we'll end up with a little bit of sludge from when the fuel evaporates they have to return the car off and this just you know helps keep the car basically fixes the idle of the car okay so one other thing that we used to have with carburetors there were a lot of adjustments and screws that we could turn to make the car idle higher in case it stalled and carburetors because they were mechanical they had a lot of adjustments fuel injection generally there's no mechanical adjustments anymore so any time that we see like a screw that has like this yellow paint on it that yellow paint should pretty much be an indication for you not to adjust it if I go ahead and adjust this screw I'm they adjust the idle by opening and closing this plate a little bit but in the process we're going to actually confuse the computer and the reason why is because the computer can't see what I did that screw there's no there's no sensor attached to the screw so if I go and change this and it don't tell the computer the computer is going to be confused and a guarantee the car is probably not going to idle properly ok so please don't go turning any screws on the throttle body assembly just because it looks like it's what we used to do on a carburetor ok when we come back we'll take a look at some of the other key sensors and what can happen when they fail alright so now that we've talked about throttle position sensor the mass airflow sensor the map sensor let's talk about a couple other key sensors here that we have on the vehicle the first guy that we're going to have is a temperature sensor and this pretty much is just a sensor that screws into either the intake manifold which is going to allow our air to come into the engine or near our thermostat and cars actually have both of these sensors usually when they actually work the same way but one measures the water temperature of the engine and one measures the air temperature of the engine and there's just two little connectors on the inside there where they're going to actually send their signal back to the computer so what the temperature sensor does is the temperature sensor tells the computer what the air temperature is or the water temperatures of the engine this is important because as air temperature changes the density of its oxygen actually changes which is again going to affect our air to fuel mixture so knowing the temperature of the engine or the air coming into the engine is a key component if this guy fails the car may deliver too much fuel when it's hot or cold or not enough fuel when it's hot or cold and in that case the car may stall so a temperature center is an important part unfortunately again you notice there's no moving parts so these things are fairly reliable okay the next sensor that we have is this little guy and this is a magnetic pickup sensor and this is has a small coil of wire inside of it with an electromagnet and it will actually generate a very weak voltage as a metal object moves past it so this is usually found on the inside of engines and transmissions and when we have that metal object swing by it sends a pulse to the computer and it tells the computer how fast something is going this little guy is what actually drives the tachometer in your car for the most part this engine speed sensor may send a signal back to the cars computer and it's going to tell the car how fast are we going okay the next sensor we have really gets a bad rap but it's probably the most important sensor when it comes to fuel efficiency and actual overall fuel injection operation and that is the oxygen sensor now the first thing is is the oxygen sensor doesn't really hang out in the oxygen okay it actually lives in the exhaust stream and it's usually located near a catalytic converter this catalytic converter actually has two oxygen sensors on it and what the oxygen sensor does is it measures the amount of oxygen content in the exhaust of the car now just a quick lesson about oxygen there's about 21% oxygen around us at all times okay the rest of it is made up with nitrogen and other gases the car really only uses the oxygen for combustion okay and the easiest way to think about combustion is just like if you were to have a campfire the more oxygen you put into the fire the bigger the fire gets the hotter it gets but if I put in too much oxygen I actually blow the flame out if I had a campfire in the middle of a windy hurricane the wind would actually blow the fire out that's an example of a fuel system that's too lean there's too much air and not enough fuel to actually run the car the other side of the coin would be is if I had that same campfire and I took an entire dump truck worth of logs and suddenly smothered the fire with all the logs the logs will my fuel but I put so much fuel on top of my hire that I actually smothered the entire fire that's an example of a car that runs too rich and the job of the oxygen sensor is to make sure that the car is not running too lean or too rich so it measures the oxygen content that comes out of the tailpipe now I just said that 21% oxygen comes into the car really only about 1% actually comes out of the tailpipe so this oxygen sensor measures that oxygen content and sends a signal back to the car's computer and that in turn tells the fuel injector exactly how much fuel to deliver to our vehicle to make it more rich or more lean it's a very very fine ratio and it works out to about roughly 15 parts of air to one part of fuel you know if your average car holds 10 gallons worth of fuel in the tank the fact is is that I would need much more oxygen I didn't need a huge oxygen tank to drive around with me fortunately air is around us all the time so we just pull it into the car and then the oxygen sensor monitors that now when the oxygen sensor starts to fail it generally is going to fail in such a way that it tells the car to start adding too much gas and the reason why car manufacturers do that is because if I take away too much fuel on it make that mixture really lean I'm going to actually run my car really hot I may run the car so hot that I actually caused things like Pistons to melt and that's a huge amount of money and a huge amount of damage and we certainly don't want that to happen so car manufacturers generally caused the sensor to over rich in the mixture when it fails over rich inning the car is generally safe with the exception of your wasting gas ok so if you have an oxygen sensor problem you know make sure that there's not something else causing that problem but the fact is is that the oxygen sensor may be the cause okay in general these guys will last around 100,000 miles if you have other mechanical problems like burning oil or burning coolant or a failed spark plug they're going to shorten the life of this sensor so don't be surprised if you end up placing that at the same time as something else okay so we have our computer we have the basic sensors okay the next thing is we have a device that is both an input and an output and this is an older-style distributor and the sensor for this guy this little magnetic pickup is right here when this little vein right here moves past that band it's going to generate a pulse just like our other magnetic sensor that's going to send a signal to the car's computer until this part the ignition coil which is an output to send a spark to the spark plug and fire our ignition system okay over here I have two other outputs this is just a fuel injector by itself you can see they're pretty harmless and they're not very big and while they can be expensive to replace the fact is is they generally don't fail that often they can get dirty over time and then need replacement but generally they can be cleaned with a special cleaning product that actually gets pushed through the injector directly the stuff that you pour into your tank or anything like that really doesn't do such a great deal to the injectors the last piece that we have that's a key output is this is a dedicated ignition coil which is much more common for what we have today the coil itself is going to have some wires on it that are going to get connected up to the computer the computer is going to tell each one of these coils when to fire my spark plug and again there's less moving parts you know there's no spark plug wires on this to replace the fact is the plug just plugs directly inside the boot right inside the coil so the old days of a tune up being a cap and rotor and spark plug and spark plug wires they're really gone these plugs they can last the vehicle if it's been running properly for about a hundred thousand miles ok so when we come back we're going to take a look at what's involved with seeing about a problem with the car when the check engine light is on alright so so now we're going to take a look at just what's involved with actually having a scan tool communicate with the car when there's a problem when you the check engine light is on and the first thing is we're going to turn on our scan tool and wait for it to boot up because it is basically a small handheld computer and while that comes on there it goes you know in order to do this it takes some specialized equipment now you can get a handheld scan tool for $100 or even less now and what they'll do is they'll just give you a number for trouble code now that trouble code is going to be correlated with the chart and the chart may say something like oxygen sensor voltage reading low okay and your first thought is well great the car is giving me a trouble code for an oxygen sensor I'm going to go out and place the oxygen sensor but that's not the right thing to do that's what a lot of amateurs do and the fact is is you really have to understand how the system works and the fact is is that if I have a broken wire on the oxygen sensor or if there's a leak in the intake manifold with the vacuum tubing or something that's going to cause that sensor to see a problem okay remember the sensor is just a messenger okay and there's that famous saying don't kill the messenger okay so don't just go replacing a part because you've got a trouble code for it all right sometimes you get lucky and that is the problem but a lot of times there's a lot more diagnostic work to be done behind it and that's why you really need to follow the repair manual okay they're Paranal is going to take it step by step and it's you know this one starts out you know pretty much just start with the basics that's always where we start in this industry is start with the basics you know we don't just go right to the expensive part and place it so now that our systems on I'm going to I'm going to scroll over here and come over to scan Diagnostics and I'm going to pick global obd2 obd2 stands for on-board diagnostics second generation the federal government mandated obd2 starting in 1996 model year and what had happened before that is that each May facture had a different connector in each car talked to different language to a computer so a Volkswagen needed a different computer and a different connector than Honda to actually communicate with the technician independent repair shops got really upset at this because they got tired of buying expensive computers and cables for every car out there on the road and federal government stepped in and said starting in 96 you got to make sure all the cars have the same connector and pretty much talk the same language and obd2 helped do that amongst a whole bunch of other things okay so I'm going to come in here to global Oh buddy to let that boot through there now I have a cable hooked up from the scan tool inside the car and the connector is up underneath the dash and most vehicles sometimes it's behind gnash tray or underneath the console but generally it's somewhere inside the passenger compartment okay so see here I got the right cable and I'm going to go turn the vehicle on so I'll be right back okay and now yep there it goes okay I just had to get rebooted there so once I'm able to communicate with the vehicle I have a number of choices I can either get trouble codes if the check engine light was on or I could do something known as a data stream and what a data stream is going to let me do is it's going to let me look at the sensors in real time now this is important just as a doctor when you go if you're not feeling good they listen to your heart they listen to your lungs they take your temperature they measure your blood pressure they want to know what's going on right now that makes you feel the way you feel and the fact is a car works the same way and right here at the top we can see a couple sensors just like we talked about I have my throttle position sensor I have an engine coolant temperature sensor and I have an intake air temperature sensor now all the sensors are working the way they're supposed to on this car and if I lean over and actuate the throttle you should be able to see the throttle change okay and that would be an indication that that throttle position sensor is working properly now if I have a problem with my air intake temperature sensor with right now it's showing that it's 97 degrees in the shop which it is 97 degrees in the shop if you happen to be watching this and it's a little cooler out we taped this in the summer but if I unplug this guy and you watch that number we can suddenly see that it triggered a code which means there was a fault recorded in the car and suddenly now the air temperature as the car sees it is minus 40 now obviously it didn't go from almost 100 degrees Fahrenheit to minus 40 in a split second but this is an example of just how unplugging one sensor can actually cause a problem and cause the check engine light to come on now at this point you know it would take nothing more than me plugging that sensor back in but if I didn't do that and I drove this car around this car has no idea what the air temperature is right now it thinks it's minus 40 out and if I drive this on a hundred degree day with it thinking the air temperatures minus 40 it's going to deliver so much fuel to this engine this car might not even start okay well because one sensor was unplucked plug this back in here okay and in a second it should there it goes and I'm showing a little bit lower cooled off a bit okay so it's important to understand that a couple things the computer doesn't actually fix the car the technician does and that our trouble code that we get is not the end-all be-all answer for the problem okay the trouble code that was just stored when I unplugged that sensor was that there was a fault with that sensor and yes there was a fault with that sensor it lost communications with the cars with the car's computer but that doesn't mean that I'm going to go through and just replace that sensor all right so hopefully you have a better understanding of vehicles and the sensors involved with them I'm Dan Reed thanks for watching car corner drive safe so just so you know I'm gonna refer to the carburetor as a toilet is that okay yeah it is okay because that's pretty much how they work I'm going to explain the best ever okay hi now wait till you hear my wait till you hear my

Channel: CCPTV53

Views: 77,203

Rating: 4.8806629 out of 5

Keywords: Education (TV Genre), Car Corner, CCP, CCPTV, car sensors, Richard Saxton, College, Community College, Philadelphia, Dan Reed, Auto Technology

Id: jyQuRgQHGCk

Length: 38min 39sec (2319 seconds)

Published: Thu Jul 17 2014