Logovideo to article
00:00 - 00:03

So today, we're explaining  all the car engine sensors

00:03 - 00:05

Every single one of them.

00:05 - 00:08

And for each of them, we're going to explain:

00:08 - 00:08

What it does.

00:09 - 00:10

How it works.

00:10 - 00:11

Where the sensor is located.

00:11 - 00:14

And what happens if it goes faulty.

00:14 - 00:18

Obviously, this is a pretty long video, with  information on 16 different sensor types.

00:18 - 00:22

So, of course, you can find timestamps  for each sensor down in the description.

00:22 - 00:26

So that you can quickly access only  the sensors you're interested in.

00:26 - 00:29

Now, although there's a lot of  sensors that are needed for the engine 

00:29 - 00:33

and the ECU(or the engine control unit) to do their job properly.

00:33 - 00:35

Many of them work in pretty similar ways.

00:35 - 00:38

They do different things, but they  have very similar characteristics.

00:38 - 00:42

And this is why to make things more  logical and easier to understand I  

00:42 - 00:45

have grouped sensors into five categories.

00:45 - 00:45

Position.

00:46 - 00:47

Air flow

00:47 - 00:48

Pressure

00:48 - 00:49

Temperature.

00:49 - 00:52

And air-fuel ratios, emissions and others.

00:52 - 00:55

And we're starting right  away with position sensors.

00:57 - 01:01

The crankshaft position sensor tells  the ECU the position of the crankshaft.

01:01 - 01:06

Because the position of the piston is fixed  in relation to the position of the crankshaft.

01:06 - 01:12

By knowing the position of the crankshaft, the ECU  also knows where the piston is inside the bore.

01:12 - 01:18

And by knowing this, it can initiate fuel injection  and/or spark ignition events, at the correct time.

01:18 - 01:22

Crankshaft position sensors are most often  either Hall effect, which is three wires.

01:22 - 01:25

Or VR(variable reluctance) which is two wires.

01:25 - 01:30

Although they work slightly differently, both  rely on the basic principles of electromagnetism,  

01:30 - 01:33

to read a trigger wheel made from a ferrous metal.

01:33 - 01:36

The trigger wheel is going to  have one or more teeth missing.

01:36 - 01:40

And whenever a missing tooth  passes in front of the sensor,  

01:40 - 01:44

it's going to change the signal  that the sensor sends to the ECU.

01:44 - 01:47

Now, the position of the missing  tooth in relation to the sensor,  

01:47 - 01:50

is going to be fixed to a certain  position of the crankshaft.

01:50 - 01:54

And by seeing the change in  the signal, the ECU can tell  

01:54 - 01:58

exactly where the crank is at that moment in time.

01:58 - 02:02

Now the ECU is also configured to the  total number of teeth on the trigger wheel.

02:02 - 02:06

And by knowing the total number of  teeth, and measuring how often the  

02:06 - 02:12

missing tooth passes in front of the sensor,  the ECU can calculate engine speed or RPM.

02:12 - 02:17

Now, every car engine has one crankshaft, and thus  it only needs one crankshaft position sensor.

02:17 - 02:22

The crankshaft position sensor in order to read  the trigger wheel must be located very near it.

02:22 - 02:25

And the trigger wheel must be  installed on something that rotates  

02:25 - 02:27

at the same speed as a crankshaft.

02:27 - 02:29

And it's usually either the crankshaft pulley,  

02:29 - 02:33

the timing gear where the timing belt or  timing chain attaches, or the flywheel.

02:33 - 02:38

So, one of these three locations is where you're  going to find your crankshaft position sensor.

02:38 - 02:42

If the sensor fails completely,  then the engine will not start.

02:42 - 02:45

Or it will start but stall  after running very briefly.

02:45 - 02:49

If the failure is not complete, then you  may get jerky or uneven acceleration,  

02:49 - 02:54

engine misfiring, rough running,  poor idle, bad mileage, and so on.

02:54 - 02:58

Now, the camshaft position sensor does the  same thing as the crankshaft position sensor.

02:58 - 02:59

But for the camshaft.

02:59 - 03:03

Now, in theory the engine can run with a crank sensor alone.

03:03 - 03:08

But adding a camshaft position sensor paints  a much more complete picture for the ECU.

03:08 - 03:10

And it's also a layer of verification for the  

03:10 - 03:13

information coming from the crankshaft position sensor.

03:13 - 03:16

Now, a camshaft position sensor lets the ECU know,  

03:16 - 03:19

what each cylinder is doing and when is it doing it.

03:19 - 03:21

And this is why it can be used for,  

03:21 - 03:25

for example, cylinder selected  knock control, sequential injection.

03:25 - 03:27

And other cylinder selective systems.

03:27 - 03:30

The cam sensor works on the same  principle as the crank sensor.

03:30 - 03:35

The only difference is, that it reads a  much smaller trigger wheel with fewer teeth,  

03:35 - 03:37

due to the size of the camshaft.

03:37 - 03:41

To read the position of the camshaft,  the cam position sensor must be near it.

03:41 - 03:44

Usually, you're going to find  it somewhere on the cam cover.

03:44 - 03:46

Either at the front or at  the back of the camshaft.

03:46 - 03:50

Or less often somewhere along  the axis of the camshaft.

03:50 - 03:55

Failure symptoms are usually the same  or very similar to a position sensor.

03:55 - 03:58

Either a no-start condition,  or poor engine running.

03:58 - 04:02

The throttle position sensor measures  the position of the throttle plate.

04:02 - 04:05

When you're operating the throttle  pedal, you're actually operating  

04:05 - 04:08

the throttle plate that's usually at  the entrance of the intake manifold.

04:08 - 04:11

When you floor it, the throttle plate gets fully  

04:11 - 04:15

opened, allowing maximum air into the  engine, for maximum acceleration.

04:15 - 04:20

By knowing the position of the throttle plate,  the ECU can know the load placed on the engine.

04:20 - 04:24

And can thus vary injection and ignition timing accordingly.

04:24 - 04:28

A throttle position sensor works  by relying on a variable resistor.

04:28 - 04:31

A variable resistor is essentially  an electrical component,  

04:31 - 04:34

which changes its electrical resistance  output based on its position.

04:34 - 04:36

It contains a movable part.

04:36 - 04:41

And different positions of this movable  part will have different resistance output.

04:41 - 04:42

In case of the throttle position sensor,  

04:42 - 04:46

the throttle plate shaft is connected  directly to the variable resistor.

04:46 - 04:50

So different positions of the throttle plate  will have different resistance outputs.

04:50 - 04:54

Which are then measured and converted  into a useful signal for the ECU,  

04:54 - 04:57

by the onboard electronics of  the throttle position sensors.

04:57 - 05:01

Now, this is what old throttle  position sensors used to work with.

05:01 - 05:02

But today,  

05:02 - 05:06

modern throttle position sensors, actually  rely on non-contact position measurements.

05:06 - 05:11

And either use Hall effect, induction or magnetic resistance  

05:11 - 05:14

to do the same job as a variable resistor.

05:14 - 05:17

Obviously, to measure the  position of the throttle plate,  

05:17 - 05:21

the throttle position sensor must be  located on the throttle body itself.

05:21 - 05:24

And this is where you always  the throttle position sensor.

05:24 - 05:27

One of the most obvious symptoms of  a failed throttle position sensor,  

05:27 - 05:29

is going to be unpredictable acceleration.

05:29 - 05:34

The car is going to feel as though it's not  correctly responding to throttle pedal inputs.

05:34 - 05:36

Also the idle will often be affected.

05:36 - 05:38

And it will either be too high or too low

05:38 - 05:41

And there also might be  difficulty starting the vehicle.

05:44 - 05:47

In addition to knowing the position  of the piston, so that it can know  

05:47 - 05:51

when to inject the fuel, the ECU must  also know how much fuel to inject.

05:51 - 05:56

And to know how much fuel to inject, it must  know how much air is coming into the engine,  

05:56 - 06:00

so that it can inject a  corresponding amount of fuel.

06:00 - 06:05

And this is exactly what a MAF(or mass  air flow) sensor does for the ECU.

06:05 - 06:09

It tells the ECU how much air  is coming into the engine.

06:09 - 06:13

Now, most MAF sensors are  either hot wire or hot film.

06:13 - 06:15

Now, they are bit different

06:15 - 06:17

And the hot film sensor is a bit more advanced.

06:17 - 06:21

But they both rely on the same basic  principle, of the very high temperature  

06:21 - 06:26

coefficient of resistance of certain  metals, such as platinum or tungsten.

06:26 - 06:30

The very high temperature coefficient of  resistance of these metals, means that even  

06:30 - 06:36

very minute changes in the temperature of  these metals, will change their resistance.

06:36 - 06:40

So when air flows over these metals,  it changes their temperature.

06:40 - 06:43

The more air flows over, the  more the resistance changes.

06:43 - 06:47

And the onboard electronics of  the MAF sensor measure this,  

06:47 - 06:50

and then convert the signal  into useful data for the ECU.

06:51 - 06:53

Now, obviously this is just  a basic working principle.

06:53 - 06:56

And a MAF sensor is more complicated  and more interesting than this.

06:56 - 07:00

But I do have a video that goes into  great detail when it comes to MAF sensors.

07:00 - 07:05

And you can find it in the description below, and  in the suggested videos in the top right corner.

07:05 - 07:10

You will usually find a MAF right after the  air cleaner housing, the air filter housing.

07:10 - 07:13

If it's not there, it's going to be  somewhere after the air filter housing,  

07:13 - 07:15

but before the throttle body.

07:15 - 07:18

If a MAF fails completely,  the engine will not start.

07:18 - 07:22

If it's only starting to fail, or  if it's a bit contaminated by dirt,  

07:22 - 07:25

then it's going to send the  wrong information to the ECU.

07:25 - 07:28

So the ECU will be injecting  the wrong amount of fuel.

07:28 - 07:30

And you can expect a rough running engine.

07:30 - 07:36

A poor idle, hesitation during acceleration,  the engine stumbling, poor mileage.

07:36 - 07:38

And other similar symptoms.

07:38 - 07:40

Now, an AFM, or airflow meter,  

07:40 - 07:44

or vane airflow meter as it's also  known, does the same thing as a MAF.

07:44 - 07:47

It measures how much air  is coming into the engine.

07:47 - 07:51

It just does it differently, and it's  usually present on older vehicles.

07:51 - 07:55

The airflow meter has a flap or a vane inside it.

07:55 - 07:58

And the incoming air pushes against this flap.

07:58 - 08:02

The more air is coming in, the more it  will push against and open the flap.

08:02 - 08:06

Now, the vane or flap is  connected to a variable resistor,  

08:06 - 08:09

just like the throttle blade shaft  of the throttle position sensor.

08:09 - 08:13

Different vane positions are going to output the resistances.

08:13 - 08:16

And then the onboard electronics are going to measure this,  

08:16 - 08:19

and convert it into a useful signal for the ECU.

08:19 - 08:24

So the different resistance outputs will tell the ECU how much the vane is open,  

08:24 - 08:27

and how much air is coming into the engine.

08:27 - 08:28

Just like the MAF sensor, 

08:28 - 08:33

the airflow meter is always going to be  somewhere near or right after the air filter.

08:33 - 08:36

Since it's doing pretty much the  same thing as a mass airflow sensor, 

08:36 - 08:39

the failure symptoms of an airflow  meter are going to be similar  

08:39 - 08:41

or the same as with a mass airflow sensor.

08:44 - 08:49

Just like the MAF or the AFM, the  MAP(manifold absolute pressure) sensor  

08:49 - 08:52

measures how much air is coming into the engine.

08:52 - 08:58

But unlike the AFM or the MAF , it does  not measure the incoming air mass directly.

08:58 - 09:02

Instead, it measures pressure  inside the engine's intake manifold,  

09:02 - 09:05

and calculates the air mass based on that.

09:05 - 09:09

The logic is that the more air  there is in an encode space,  

09:09 - 09:14

the greater the pressure that air is going  to exert onto the walls of that cold space.

09:14 - 09:18

And this is exactly what the MAP is using And by measuring the pressure,  

09:18 - 09:22

it can calculate how much air is coming into the engine.

09:22 - 09:27

The MAP sensor measures intake air pressure, by  relying on a tiny micromachined silicon chip.

09:27 - 09:33

The silicone chip consists of a silicon  membrane, and a tiny piezoelectric material.

09:33 - 09:37

The piezoelectric material reacts to  the flexing of the silicon membrane,  

09:37 - 09:41

under pressure, by changing its electrical charge.

09:41 - 09:42

The more the pressure there is,

09:42 - 09:44

the more the silicon membrane flexes,

09:44 - 09:46

the more the charge changes.

09:46 - 09:52

And the onboard electronics measure this, and  then convert it into a useful signal for the ECU.

09:52 - 09:56

Now, if you're building a performance engine  or significantly increasing the boost levels  

09:56 - 10:02

of your engine, then the stock MAP sensor will no  longer be adequate and will need to be upgraded.

10:02 - 10:07

Now, AEM carries a whole range  of robust, reliable, and accurate  

10:07 - 10:09

MAP sensors to suit all needs.

10:09 - 10:11

If you need them, check'em out below

10:11 - 10:15

Because the MAP must measure  pressure directly in the intake  

10:15 - 10:19

manifold, it's also always located  somewhere on the intake manifold.

10:19 - 10:23

And again, because it's ultimately  trying to measure the incoming air mass,  

10:23 - 10:28

failure symptoms are going to be similar  or the same as with a MAF or AFM.

10:28 - 10:31

The oil pressure sensor obviously  measures oil pressure inside the engine.

10:31 - 10:36

It's a very simple, but perhaps one of the most  important and vital sensors for the engine.

10:36 - 10:42

Because without enough oil pressure, the engine is  going to sustain catastrophic damage very quickly 

10:42 - 10:44

Just like many other pressure sensors on a car,  

10:44 - 10:48

the oil pressure sensor is basically  a piezoresistive pressure transducer.

10:48 - 10:53

Meaning that it works on pretty much the same  basic principle as the MAP sensor we just covered.

10:53 - 10:58

It's simply calibrated for the different  values expected from the engine's oil pressure.

10:58 - 11:02

Now in some cases, the oil pressure sensor  of an engine is not a sensor at all.

11:02 - 11:03

It's just a switch.

11:03 - 11:06

And the most basic version contains a diaphragm.

11:06 - 11:09

Which when it flexes, it simply causes  

11:09 - 11:13

an electric circuit, and reports that  there is sufficient oil pressure.

11:13 - 11:17

If there isn't enough oil pressure, the  diaphragm isn't going to flex enough.

11:17 - 11:19

It won't be able to cause the electric circuit.

11:19 - 11:23

And an oil pressure light is going  to illuminate, warning the driver  

11:23 - 11:26

that the engine should be  shut down to prevent damage.

11:26 - 11:29

The oil pressure sensor is usually  located somewhere on the engine block,  

11:29 - 11:31

often near the oil filter.

11:31 - 11:35

But it can be anywhere on the engine  block, where it can be tapped directly  

11:35 - 11:40

into an engine oil passage, so that it  can accurately read the oil pressure.

11:40 - 11:44

A lack of oil pressure is one of the single  most dangerous situations for an engine.

11:44 - 11:47

So if the oil pressure sensor is malfunctioning

11:47 - 11:50

and falsely reporting whole  oil pressure to the ECU,

11:50 - 11:53

then the ECU will falsely  trigger a limp home mode,

11:53 - 11:55

or will refuse to start the engine.

11:55 - 11:58

Obviously, the fuel pressure  sensor measures fuel pressure.

11:58 - 11:59

That's what it does.

11:59 - 12:02

So why is it important to measure fuel pressure?

12:02 - 12:06

Well by knowing the fuel pressure  of the fuel inside the fuel rail,  

12:06 - 12:10

the ECU can know how long to open the injectors,  

12:10 - 12:15

in order to ensure that the correct amount  of fuel is injected into the engine.

12:15 - 12:18

In order to measure fuel pressure  right inside the fuel rail,  

12:18 - 12:23

the fuel pressure sensor is almost always  located somewhere directly on the fuel rail.

12:23 - 12:27

Usually, the first symptom of  failure is difficulty starting.

12:27 - 12:28

Especially on a cold engine.

12:28 - 12:32

Other symptoms include poor  acceleration and poor mileage.

12:34 - 12:37

Now the IAT sensor (or the intake air temperature sensor)

12:37 - 12:40

Obviously measures the  temperature of the intake air.

12:40 - 12:44

Now, it's important to do this, because air  density is influenced by air temperature.

12:44 - 12:47

The hotter the air, the  less dense it's going to be,

12:47 - 12:50

and the less molecules of air  are going to be in a given space.

12:50 - 12:54

Although in theory, an engine could  run without an air intake sensor,  

12:54 - 12:56

it's still a very good idea to have one.

12:56 - 12:59

And the engine's going to run  better with it, than without it.

12:59 - 13:03

The IAT sensor works together  with the MAF, MAP, or AFM 

13:03 - 13:07

to give the ECU a more complete picture  of the air coming into the engine.

13:07 - 13:10

Which helps reduce emissions and  improve power and efficiency.

13:10 - 13:15

Just like almost all the other temperature  sensors in a car, the IAT sensor is a thermister.

13:15 - 13:17

Meaning that its electrical  resistance is going to change,  

13:17 - 13:20

in response to the changes in its temperature.

13:20 - 13:25

And then as usual, the resistance is measured  and converted into a useful signal for the ECU.

13:25 - 13:29

The IAT sensor is often integrated  into the MAF or the AFM.

13:29 - 13:33

If it's not there, you can usually  find it somewhere in the intake duct.

13:33 - 13:34

Usually near the throttle body.

13:34 - 13:36

If you're building a performance or racing engine,

13:36 - 13:39

and you need to add an intake  air temperature sensor,

13:39 - 13:41

then AEM has the right one for you.

13:41 - 13:42

It's easy to install

13:42 - 13:43

And it's reliable and accurate.

13:43 - 13:46

As always, links are down below.

13:46 - 13:48

If there's only a bit of dirt on the IAT sensor,  

13:48 - 13:51

then malfunction symptoms are going  to be very mild and barely noticeable.

13:51 - 13:56

If the fault is more severe, then the engine  may run rough, stumble, or even stall.

13:56 - 13:59

Or it can have very mild, short surges of power.

13:59 - 14:02

All the remaining temperature sensors  we're going to cover are also thermisters,  

14:02 - 14:05

so we won't be individually  explaining how each one of them works.

14:05 - 14:08

We'll just talk but they do  where they are and so on.

14:08 - 14:10

So let's proceed with the  coolant temperature sensor.

14:10 - 14:13

Now, the coolant temperature sensor  is very important for the ECU

14:13 - 14:16

Because it tells it how warm the engine is.

14:16 - 14:18

This is important because a cold engine  

14:18 - 14:21

needs a different amount of fuel,  when compared to a hot engine.

14:21 - 14:24

The coolant temperature sensor is also  needed to trigger various actions.

14:24 - 14:26

Such as for example starting the radiator fans

14:26 - 14:31

Or if the engine is overheating, it can  tell the ECU to trigger limp home mode.

14:31 - 14:34

Or refuse to start the engine,  until it cools back down.

14:34 - 14:35

Like almost all the other temperature sensors,

14:35 - 14:38

the coolant temp sensor must  come into direct contact

14:38 - 14:40

with the fluid whose temperature  it's trying to measure.

14:40 - 14:44

As such we are very often going to find the  coolant temp sensor at or near the thermostat.

14:44 - 14:48

Some cars have more than one, and you can  find them anywhere on the coolant piping,  

14:48 - 14:50

or wherever else coolant is passing through.

14:50 - 14:53

A cold engine needs more fuel than a hot engine.

14:53 - 14:56

This means that if the coolant  temperature sensor is malfunctioning,  

14:56 - 14:59

and telling the ECU that the engine  is cold, even though it's hot.

14:59 - 15:03

The ECU is going to inject extra fuel, which  is going to result in a rich running condition.

15:03 - 15:05

And this means you're going to get poor mileage,  

15:05 - 15:08

or even black smoke from  the exhaust in severe cases.

15:08 - 15:12

An opposite scenario is also possible, and  the ECU can think that the engine is hot,  

15:12 - 15:13

even though it's cold.

15:13 - 15:16

In that case, it's going  to inject too little fuel.

15:16 - 15:18

Which is going to lead to  a lean running condition.

15:18 - 15:22

And this can lead to the engine misfiring,  or even knocking, until it heats up.

15:22 - 15:26

Fuel temperature must be measured because  fuel density, just like the density of air,  

15:26 - 15:28

is affected by temperature.

15:28 - 15:31

Hot fuel is less dense and burns more easily,  

15:31 - 15:34

so a bit more of it must be  injected to compensate for this.

15:34 - 15:38

The fuel temperature sensor is most  often located somewhere at the fuel tank.

15:38 - 15:41

Often as part of the fuel pump assembly.

15:41 - 15:44

Less often it can be found  somewhere else along the fuel lines.

15:44 - 15:47

The information coming from the fuel  temperature sensor is only used to  

15:47 - 15:51

further improve the injection accuracy, in  order to meet stringent emission standards.

15:51 - 15:54

An engine can run pretty well with  a faulty fuel temperature sensor,  

15:54 - 15:58

and in some cases symptoms  might not be noticeable at all.

15:58 - 16:01

If the fault is more severe or  if the sensor component fails,  

16:01 - 16:03

then the vehicle might fail in emissions test.

16:03 - 16:06

Or get slightly worse mileage  and performance than usual.

16:06 - 16:10

Automatic cars only have an oil pressure  sensor, and do not measure oil temperature

16:10 - 16:14

Measuring oil temperature can be a  useful additional layer of protection.

16:14 - 16:18

If the oil overheats, this is going  to negatively impact its viscosity,  

16:18 - 16:23

and the oil won't be capable of doing its  job, which can lead to engine failure.

16:23 - 16:27

Now the ECU, by seeing the oil temperature,  can activate the limp home mode,  

16:27 - 16:31

or refuse to start the engine, before  oil temperature normalize again.

16:31 - 16:35

In addition to relaying information to  the ECU, the oil temperature sensor can  

16:35 - 16:38

also relay information to engage,  or display visible to the driver.

16:38 - 16:41

And then the driver can take preemptive action,  

16:41 - 16:44

and shut the engine down if  oil temperatures get too high.

16:44 - 16:46

In order to be able to measure the temperatures of  

16:46 - 16:50

oil, the sensor must come into direct  contact with the oil inside the engine.

16:50 - 16:54

As such it's often found on the engine  block, or less often on the cylinder head.

16:54 - 16:58

In newer cars, it can be found  integrated into the oil level sensor.

16:58 - 17:01

Depending on how it fails, a  malfunctioning oil temperature  

17:01 - 17:04

sensor might make the ECU think that  the oil temperatures are too high.

17:04 - 17:05

Even though they aren't.

17:05 - 17:08

And then the ECU might incorrectly  trigger a limp home mode.

17:08 - 17:13

The sensor can also malfunction in a way that  it fails to report overly high oil temperatures,  

17:13 - 17:15

which can result in engine damage.

17:15 - 17:20

A faulty oil temperature sensor is very easy  to spot, if there's a gauge or display for it.

17:24 - 17:28

The O2 or the oxygen sensor measures the  amount of oxygen present in the exhaust gases.

17:28 - 17:31

The amount of oxygen present in exhaust gases,  

17:31 - 17:36

directly corresponds to the amount of  fuel burned inside the combustion chamber.

17:36 - 17:39

By measuring the oxygen, the oxygen  sensor can actually tell the ECU  

17:39 - 17:42

the air-fuel ratio at which the engine is running.

17:42 - 17:47

Now, the air-fuel ratio, or the ratio of  air to fuel inside the combustion chamber,  

17:47 - 17:51

is absolutely critical for both  engine performance and emissions.

17:51 - 17:55

And must be constantly monitored to  ensure that it is where it needs to be.

17:55 - 17:57

We have two kinds of oxygen sensors.

17:57 - 17:59

Narrowband and wideband.

17:59 - 18:03

Narrowband sensors can tell if the  engine is running rich or lean.

18:03 - 18:09

But they cannot tell exactly, how rich  or how lean the engine is running.

18:09 - 18:14

On the other hand, the wide band sensor  covers a much wider range of air-fuel ratios.

18:14 - 18:19

And you can tell the ECU exactly how  rich or lean the engine is running.

18:19 - 18:22

Although it's small, the oxygen  sensor is a pretty complicated device.

18:22 - 18:26

It involves zirconium bulbs, and  various platings and what not.

18:26 - 18:30

And explaining it in this video would really  make the video too long and complicated.

18:30 - 18:34

So, for the purposes of this video what I  will tell you, is that the amount of oxygen  

18:34 - 18:39

measured at the sensor tip, corresponds  to a voltage produced by the sensor.

18:39 - 18:44

So for example, 0.5 volts is going  to be near the ideal air-fuel ratios.

18:44 - 18:48

And at the other far ends of the spectrum,  we can find too rich and too lean.

18:48 - 18:52

So what the ECU is going to do, it's going  to increase or decrease the amount of fuel  

18:52 - 18:57

injected, in order to reach again  the ideal air-fuel targeted ratio.

18:57 - 19:02

Now, most catalytic converter equipped cars, are  going to have a minimum of two oxygen sensors.

19:02 - 19:05

One is going to be before, and  one after the catalytic converter.

19:05 - 19:08

The one before the catalytic converter  is called the upstream oxygen sensor,  

19:08 - 19:12

and it's usually going to be right at  the exhaust manifold, or right behind it.

19:12 - 19:17

And it's used to see the exact air-fuel  ratio at which the engine is running.

19:17 - 19:21

The one after the catalytic converter, that  sensor is called the downstream sensor.

19:21 - 19:26

And it's used to verify that the catalytic  converter is properly doing its job.

19:26 - 19:29

Failure symptoms can range from  barely noticeable, to very noticeable.

19:29 - 19:35

But even if the symptoms are hard to notice, the  vehicle is likely going to fail an emissions test.

19:35 - 19:38

Now, if it's noticeable, it's  going to be really noticeable.

19:38 - 19:39

The engine is going to run rough

19:39 - 19:43

Especially on more modern cars, which  rely more heavily on the oxygen sensor.

19:43 - 19:49

More modern cars, can even refuse to start the  engine if the sensor has completely failed.

19:49 - 19:53

If you know that you have a bad oxygen  sensor, then it's a really good idea  

19:53 - 19:57

to replace it as soon as possible,  even if the vehicle is running okay.

19:57 - 20:01

Because an overly rich running condition,  can lead to your catalytic converter  

20:01 - 20:03

failing far more sooner than it needs to.

20:04 - 20:08

Now, wide-band oxygen sensors are  also an absolutely critical tool 

20:08 - 20:10

for tuning performance and racing engines.

20:10 - 20:14

And the AEM carries one of the most  popular, and the fastest responding,  

20:14 - 20:16

wideband setup on the market.

20:16 - 20:18

Links are below.

20:18 - 20:21

An EGT is an exhaust gas temperature sensor.

20:21 - 20:25

And as the name reveals, it measures  the temperature of the exhaust gas.

20:25 - 20:29

Now, an EGT is a probe that must be  present directly in the exhaust stream,  

20:29 - 20:32

in order to measure the  temperature of the exhaust gas.

20:32 - 20:37

By measuring the temperature of the exhaust, we  can infer information about the air-fuel ratio.

20:37 - 20:42

Because changes in the air-fuel ratio,  are also going to be directly correlated  

20:42 - 20:44

with changes in the exhaust gas temperature.

20:44 - 20:47

Now, an EGT probe isn't often  used on gasoline engines.

20:47 - 20:52

But it can be useful to protect the turbo, and  the catalytic converter from thermal overall.

20:52 - 20:56

Now, EGT probes are often used on  turbo diesel and diesel engines 

20:56 - 21:00

to verify that the DPF(or diesel particular filter) has reached a  

21:00 - 21:02

sufficiently high temperature for regeneration.

21:02 - 21:07

They're also useful for protecting the  SCR(or selective catalyst reduction) 

21:07 - 21:12

in LNT(or lean NOx trap) and other NOx absorbing systems.

21:12 - 21:16

Although it's considered an old tool when it  comes to tuning performance and racing engines,  

21:16 - 21:20

an EGT probe can still be a very  useful tool that provides valuable  

21:20 - 21:22

insight into what's happening inside the engine.

21:22 - 21:27

Naturally, AEM has some very sleek  EGT setups, that you can check out.

21:27 - 21:30

In order to get the most accurate  reading of exhaust gas temperatures,  

21:30 - 21:33

the EGT probe must be as close to  the exhaust valves as possible.

21:33 - 21:38

This is why you're always going to find it in the  exhaust manifold very close to the cylinder head.

21:38 - 21:40

The other location is always going to be after  

21:40 - 21:44

the DPF, or diesel particular filter,  to verify if the DPF is doing its job.

21:44 - 21:48

EGT probes are very rarely present from the factory gasoline engines,  

21:48 - 21:52

so really aren't any very  common symptoms to discuss.

21:52 - 21:53

When it comes to diesel vehicles.

21:54 - 21:59

An EGT failure is going to cause the vehicle  to go into regeneration mode very often.

21:59 - 22:02

And regeneration mode is going  to last longer than usual.

22:02 - 22:05

And you may also get poor  mileage and poor performance.

22:05 - 22:07

Now, NOx are nitrogen oxide sensors.

22:07 - 22:10

And they measure the amount of  nitrogen oxides in the exhaust gases.

22:10 - 22:13

They're usually only present on diesel vehicles,  

22:13 - 22:17

and were briefly present on some stratified  charged gasoline engines in the past.

22:17 - 22:21

Their main role is to verify the  correct operation of the SCR.

22:21 - 22:23

Or the selective catalyst reduction system.

22:23 - 22:26

This is an active emission  system in diesel vehicles,  

22:26 - 22:31

which injects ammonia or diesel emissions  fluid, directly into the exhaust gases.

22:31 - 22:37

And this converts the nitrogen oxides into  nitrogen, water and minute amounts of CO2.

22:37 - 22:40

There's usually two of these  sensors in a diesel vehicle

22:40 - 22:43

One before, and one after the  selective catalyst reduction system.

22:43 - 22:47

The one before, measures how  much much nitrogen is coming in.

22:47 - 22:50

And the one after measures how  much nitrogen oxide is coming out,  

22:50 - 22:54

to make sure that the selective catalyst  reduction system is doing its job.

22:54 - 22:58

A failure is going to trigger most modern  diesel vehicles to go into a "limp mode home".

22:58 - 23:01

You also might get an erratic  idle, and poor mileage.

23:01 - 23:04

Now 'knock' is abnormal  combustion inside the engine.

23:04 - 23:10

If it's strong enough, and if it persists long  enough, it can cause catastrophic engine damage.

23:10 - 23:13

A knock sensor is essentially a microphone.

23:13 - 23:17

Tuned to listen to the specific  frequency of knock inside the engine.

23:17 - 23:18

This depends on the engine,  

23:18 - 23:22

but largely it actually depends on  the bore and stroke of that engine.

23:22 - 23:27

If the knock sensor detects knock, it's  going to relay this information to the ECU.

23:27 - 23:31

And the ECU is going to respond, by  either retarding ignition timing,  

23:31 - 23:33

or increasing the amount of  fuel injected into the engine.

23:33 - 23:36

To prevent the knock from occurring again.

23:36 - 23:40

In order to be capable of hearing the knock  resonating throughout the engine block,  

23:40 - 23:43

the knock sensor is always  going to be on the engine block.

23:43 - 23:49

Many engines with six or more cylinders have  two or even knock sensors in some cases.

23:49 - 23:53

In many cases, a knock sensor's failure will have  zero effect on the way the engine is running.

23:53 - 23:57

You might get a check engine light, but  the engine will run completely normal.

23:57 - 24:02

Now, the scenario is a bit different on more  modern cars, whose ECU once it detects knock  

24:02 - 24:09

sensor failure, is going to often trigger a limp  home mode, until the knock sensor is replaced.

25:52 - 25:54

And there you have it.

25:54 - 25:55

All the sensors.

25:55 - 25:56

Is it really all the sensors?

25:56 - 25:57

Well, likely not

25:57 - 26:01

Because the number of sensors on  modern engines is growing everyday.

26:01 - 26:05

And by the time I was shooting this video,  somebody might have invented something new.

26:05 - 26:07

So if I did miss a sensor, let me know.

26:07 - 26:09

Also, if you want a more in-depth video  

26:09 - 26:12

on any of the sensors in this  video, tell me about that as well.

26:13 - 26:14

So yeah, that's pretty much it for today.

26:14 - 26:16

As always thanks a lot for watching.

26:16 - 26:19

And I'll be seeing you soon,  with more fun and useful stuff.

26:19 - 26:21

On the D4A channel.

Understanding Car Engine Sensors: From Crankshaft to Knock - A Comprehensive Guide

This detailed guide dives deep into understanding the various car engine sensors that play crucial roles in ensuring your vehicle runs smoothly and efficiently. From position sensors to air-fuel ratios and emissions, each sensor is explained in terms of its function, working mechanism, location, and potential consequences of malfunction. The article categorizes sensors into Position, Air Flow, Pressure, Temperature, and Air-Fuel Ratios, Emissions, and Others, offering a logical and structured breakdown of this complex topic.

Starting with the crankshaft position sensor, this sensor informs the ECU about the crankshaft's position, enabling precise timing for fuel injection and spark ignition. Moving on to the camshaft position sensor, we see how it complements the crankshaft sensor to provide a complete picture of cylinder actions. The throttle position sensor is vital in determining engine load based on throttle plate position, influencing injection and ignition timing.

Exploring further, the MAF sensor measures incoming air to adjust fuel injection accurately, while the AFM does a similar job using a different mechanism. MAP sensors calculate air mass indirectly via pressure measurements, contributing to efficient engine performance.

Oil pressure sensors and fuel temperature sensors ensure proper lubrication and fuel injection, respectively. Temperature sensors like the coolant temp sensor and IAT sensor directly impact engine efficiency by monitoring temperature variations.

The article elucidates the significance of wideband oxygen sensors in gauging air-fuel ratios precisely, followed by insights on EGT sensors and the critical role they play in safeguarding engines, especially in restrained air environments like turbochargers.

Touching on the NOx sensors on diesel vehicles ensures compliance with emission standards, while knock sensors detect abnormal combustion, providing real-time feedback to prevent engine damage.

In conclusion, this detailed guide serves as an invaluable resource for understanding the intricate network of car engine sensors that are essential for optimal engine performance. Despite covering a wide array of sensors, it acknowledges the dynamic nature of automotive technology, with new sensors possibly emerging. Dive into this comprehensive sensor saga for an illuminating glimpse into your vehicle's inner workings.

Remember, keeping these sensors in top condition ensures your engine operates at its best, providing a smoother driving experience and enhanced efficiency. So next time you hear a sensor's name, you'll know exactly how it contributes to your car's performance. Happy driving, and stay tuned for more exciting insights from the D4A channel!