So today, we're explaining
all the car engine sensors Every single one of them. And for each of them, we're going to explain: What it does. How it works. Where the sensor is located. And what happens if it goes faulty. Obviously, this is a pretty long video, with
information on 16 different sensor types. So, of course, you can find timestamps
for each sensor down in the description. So that you can quickly access only
the sensors you're interested in. Now, although there's a lot of
sensors that are needed for the engine and the ECU(or the engine control unit)
to do their job properly. Many of them work in pretty similar ways. They do different things, but they
have very similar characteristics. And this is why to make things more
logical and easier to understand I have grouped sensors into five categories. Position. Air flow Pressure Temperature. And air-fuel ratios, emissions and others. And we're starting right
away with position sensors. The crankshaft position sensor tells
the ECU the position of the crankshaft. Because the position of the piston is fixed
in relation to the position of the crankshaft. By knowing the position of the crankshaft, the ECU
also knows where the piston is inside the bore. And by knowing this, it can initiate fuel injection
and/or spark ignition events, at the correct time. Crankshaft position sensors are most often
either Hall effect, which is three wires. Or VR(variable reluctance) which is two wires. Although they work slightly differently, both
rely on the basic principles of electromagnetism, to read a trigger wheel made from a ferrous metal. The trigger wheel is going to
have one or more teeth missing. And whenever a missing tooth
passes in front of the sensor, it's going to change the signal
that the sensor sends to the ECU. Now, the position of the missing
tooth in relation to the sensor, is going to be fixed to a certain
position of the crankshaft. And by seeing the change in
the signal, the ECU can tell exactly where the crank is at that moment in time. Now the ECU is also configured to the
total number of teeth on the trigger wheel. And by knowing the total number of
teeth, and measuring how often the missing tooth passes in front of the sensor,
the ECU can calculate engine speed or RPM. Now, every car engine has one crankshaft, and thus
it only needs one crankshaft position sensor. The crankshaft position sensor in order to read
the trigger wheel must be located very near it. And the trigger wheel must be
installed on something that rotates at the same speed as a crankshaft. And it's usually either the crankshaft pulley, the timing gear where the timing belt or
timing chain attaches, or the flywheel. So, one of these three locations is where you're
going to find your crankshaft position sensor. If the sensor fails completely,
then the engine will not start. Or it will start but stall
after running very briefly. If the failure is not complete, then you
may get jerky or uneven acceleration, engine misfiring, rough running,
poor idle, bad mileage, and so on. Now, the camshaft position sensor does the
same thing as the crankshaft position sensor. But for the camshaft. Now, in theory the engine can run with a crank sensor alone. But adding a camshaft position sensor paints
a much more complete picture for the ECU. And it's also a layer of verification for the information coming from the crankshaft position sensor. Now, a camshaft position sensor lets the ECU know, what each cylinder is doing and when is it doing it. And this is why it can be used for, for example, cylinder selected
knock control, sequential injection. And other cylinder selective systems. The cam sensor works on the same
principle as the crank sensor. The only difference is, that it reads a
much smaller trigger wheel with fewer teeth, due to the size of the camshaft. To read the position of the camshaft,
the cam position sensor must be near it. Usually, you're going to find
it somewhere on the cam cover. Either at the front or at
the back of the camshaft. Or less often somewhere along
the axis of the camshaft. Failure symptoms are usually the same
or very similar to a position sensor. Either a no-start condition,
or poor engine running. The throttle position sensor measures
the position of the throttle plate. When you're operating the throttle
pedal, you're actually operating the throttle plate that's usually at
the entrance of the intake manifold. When you floor it, the throttle plate gets fully opened, allowing maximum air into the
engine, for maximum acceleration. By knowing the position of the throttle plate,
the ECU can know the load placed on the engine. And can thus vary injection and ignition timing accordingly. A throttle position sensor works
by relying on a variable resistor. A variable resistor is essentially
an electrical component, which changes its electrical resistance
output based on its position. It contains a movable part. And different positions of this movable
part will have different resistance output. In case of the throttle position sensor, the throttle plate shaft is connected
directly to the variable resistor. So different positions of the throttle plate
will have different resistance outputs. Which are then measured and converted
into a useful signal for the ECU, by the onboard electronics of
the throttle position sensors. Now, this is what old throttle
position sensors used to work with. But today, modern throttle position sensors, actually
rely on non-contact position measurements. And either use Hall effect, induction or magnetic resistance to do the same job as a variable resistor. Obviously, to measure the
position of the throttle plate, the throttle position sensor must be
located on the throttle body itself. And this is where you always
the throttle position sensor. One of the most obvious symptoms of
a failed throttle position sensor, is going to be unpredictable acceleration. The car is going to feel as though it's not
correctly responding to throttle pedal inputs. Also the idle will often be affected. And it will either be too high or too low And there also might be
difficulty starting the vehicle. In addition to knowing the position
of the piston, so that it can know when to inject the fuel, the ECU must
also know how much fuel to inject. And to know how much fuel to inject, it must
know how much air is coming into the engine, so that it can inject a
corresponding amount of fuel. And this is exactly what a MAF(or mass
air flow) sensor does for the ECU. It tells the ECU how much air
is coming into the engine. Now, most MAF sensors are
either hot wire or hot film. Now, they are bit different And the hot film sensor is a bit more advanced. But they both rely on the same basic
principle, of the very high temperature coefficient of resistance of certain
metals, such as platinum or tungsten. The very high temperature coefficient of
resistance of these metals, means that even very minute changes in the temperature of
these metals, will change their resistance. So when air flows over these metals,
it changes their temperature. The more air flows over, the
more the resistance changes. And the onboard electronics of
the MAF sensor measure this, and then convert the signal
into useful data for the ECU. Now, obviously this is just
a basic working principle. And a MAF sensor is more complicated
and more interesting than this. But I do have a video that goes into
great detail when it comes to MAF sensors. And you can find it in the description below, and
in the suggested videos in the top right corner. You will usually find a MAF right after the
air cleaner housing, the air filter housing. If it's not there, it's going to be
somewhere after the air filter housing, but before the throttle body. If a MAF fails completely,
the engine will not start. If it's only starting to fail, or
if it's a bit contaminated by dirt, then it's going to send the
wrong information to the ECU. So the ECU will be injecting
the wrong amount of fuel. And you can expect a rough running engine. A poor idle, hesitation during acceleration,
the engine stumbling, poor mileage. And other similar symptoms. Now, an AFM, or airflow meter, or vane airflow meter as it's also
known, does the same thing as a MAF. It measures how much air
is coming into the engine. It just does it differently, and it's
usually present on older vehicles. The airflow meter has a flap or a vane inside it. And the incoming air pushes against this flap. The more air is coming in, the more it
will push against and open the flap. Now, the vane or flap is
connected to a variable resistor, just like the throttle blade shaft
of the throttle position sensor. Different vane positions are going to output the resistances. And then the onboard electronics are going to measure this, and convert it into a useful signal for the ECU. So the different resistance outputs
will tell the ECU how much the vane is open, and how much air is coming into the engine. Just like the MAF sensor, the airflow meter is always going to be
somewhere near or right after the air filter. Since it's doing pretty much the
same thing as a mass airflow sensor, the failure symptoms of an airflow
meter are going to be similar or the same as with a mass airflow sensor. Just like the MAF or the AFM, the
MAP(manifold absolute pressure) sensor measures how much air is coming into the engine. But unlike the AFM or the MAF , it does
not measure the incoming air mass directly. Instead, it measures pressure
inside the engine's intake manifold, and calculates the air mass based on that. The logic is that the more air
there is in an encode space, the greater the pressure that air is going
to exert onto the walls of that cold space. And this is exactly what the MAP is using
And by measuring the pressure, it can calculate how much air is coming into the engine. The MAP sensor measures intake air pressure, by
relying on a tiny micromachined silicon chip. The silicone chip consists of a silicon
membrane, and a tiny piezoelectric material. The piezoelectric material reacts to
the flexing of the silicon membrane, under pressure, by changing its electrical charge. The more the pressure there is, the more the silicon membrane flexes, the more the charge changes. And the onboard electronics measure this, and
then convert it into a useful signal for the ECU. Now, if you're building a performance engine
or significantly increasing the boost levels of your engine, then the stock MAP sensor will no
longer be adequate and will need to be upgraded. Now, AEM carries a whole range
of robust, reliable, and accurate MAP sensors to suit all needs. If you need them, check'em out below Because the MAP must measure
pressure directly in the intake manifold, it's also always located
somewhere on the intake manifold. And again, because it's ultimately
trying to measure the incoming air mass, failure symptoms are going to be similar
or the same as with a MAF or AFM. The oil pressure sensor obviously
measures oil pressure inside the engine. It's a very simple, but perhaps one of the most
important and vital sensors for the engine. Because without enough oil pressure, the engine is
going to sustain catastrophic damage very quickly Just like many other pressure sensors on a car, the oil pressure sensor is basically
a piezoresistive pressure transducer. Meaning that it works on pretty much the same
basic principle as the MAP sensor we just covered. It's simply calibrated for the different
values expected from the engine's oil pressure. Now in some cases, the oil pressure sensor
of an engine is not a sensor at all. It's just a switch. And the most basic version contains a diaphragm. Which when it flexes, it simply causes an electric circuit, and reports that
there is sufficient oil pressure. If there isn't enough oil pressure, the
diaphragm isn't going to flex enough. It won't be able to cause the electric circuit. And an oil pressure light is going
to illuminate, warning the driver that the engine should be
shut down to prevent damage. The oil pressure sensor is usually
located somewhere on the engine block, often near the oil filter. But it can be anywhere on the engine
block, where it can be tapped directly into an engine oil passage, so that it
can accurately read the oil pressure. A lack of oil pressure is one of the single
most dangerous situations for an engine. So if the oil pressure sensor is malfunctioning and falsely reporting whole
oil pressure to the ECU, then the ECU will falsely
trigger a limp home mode, or will refuse to start the engine. Obviously, the fuel pressure
sensor measures fuel pressure. That's what it does. So why is it important to measure fuel pressure? Well by knowing the fuel pressure
of the fuel inside the fuel rail, the ECU can know how long to open the injectors, in order to ensure that the correct amount
of fuel is injected into the engine. In order to measure fuel pressure
right inside the fuel rail, the fuel pressure sensor is almost always
located somewhere directly on the fuel rail. Usually, the first symptom of
failure is difficulty starting. Especially on a cold engine. Other symptoms include poor
acceleration and poor mileage. Now the IAT sensor
(or the intake air temperature sensor) Obviously measures the
temperature of the intake air. Now, it's important to do this, because air
density is influenced by air temperature. The hotter the air, the
less dense it's going to be, and the less molecules of air
are going to be in a given space. Although in theory, an engine could
run without an air intake sensor, it's still a very good idea to have one. And the engine's going to run
better with it, than without it. The IAT sensor works together
with the MAF, MAP, or AFM to give the ECU a more complete picture
of the air coming into the engine. Which helps reduce emissions and
improve power and efficiency. Just like almost all the other temperature
sensors in a car, the IAT sensor is a thermister. Meaning that its electrical
resistance is going to change, in response to the changes in its temperature. And then as usual, the resistance is measured
and converted into a useful signal for the ECU. The IAT sensor is often integrated
into the MAF or the AFM. If it's not there, you can usually
find it somewhere in the intake duct. Usually near the throttle body. If you're building a performance or racing engine, and you need to add an intake
air temperature sensor, then AEM has the right one for you. It's easy to install And it's reliable and accurate. As always, links are down below. If there's only a bit of dirt on the IAT sensor, then malfunction symptoms are going
to be very mild and barely noticeable. If the fault is more severe, then the engine
may run rough, stumble, or even stall. Or it can have very mild, short surges of power. All the remaining temperature sensors
we're going to cover are also thermisters, so we won't be individually
explaining how each one of them works. We'll just talk but they do
where they are and so on. So let's proceed with the
coolant temperature sensor. Now, the coolant temperature sensor
is very important for the ECU Because it tells it how warm the engine is. This is important because a cold engine needs a different amount of fuel,
when compared to a hot engine. The coolant temperature sensor is also
needed to trigger various actions. Such as for example starting the radiator fans Or if the engine is overheating, it can
tell the ECU to trigger limp home mode. Or refuse to start the engine,
until it cools back down. Like almost all the other temperature sensors, the coolant temp sensor must
come into direct contact with the fluid whose temperature
it's trying to measure. As such we are very often going to find the
coolant temp sensor at or near the thermostat. Some cars have more than one, and you can
find them anywhere on the coolant piping, or wherever else coolant is passing through. A cold engine needs more fuel than a hot engine. This means that if the coolant
temperature sensor is malfunctioning, and telling the ECU that the engine
is cold, even though it's hot. The ECU is going to inject extra fuel, which
is going to result in a rich running condition. And this means you're going to get poor mileage, or even black smoke from
the exhaust in severe cases. An opposite scenario is also possible, and
the ECU can think that the engine is hot, even though it's cold. In that case, it's going
to inject too little fuel. Which is going to lead to
a lean running condition. And this can lead to the engine misfiring,
or even knocking, until it heats up. Fuel temperature must be measured because
fuel density, just like the density of air, is affected by temperature. Hot fuel is less dense and burns more easily, so a bit more of it must be
injected to compensate for this. The fuel temperature sensor is most
often located somewhere at the fuel tank. Often as part of the fuel pump assembly. Less often it can be found
somewhere else along the fuel lines. The information coming from the fuel
temperature sensor is only used to further improve the injection accuracy, in
order to meet stringent emission standards. An engine can run pretty well with
a faulty fuel temperature sensor, and in some cases symptoms
might not be noticeable at all. If the fault is more severe or
if the sensor component fails, then the vehicle might fail in emissions test. Or get slightly worse mileage
and performance than usual. Automatic cars only have an oil pressure
sensor, and do not measure oil temperature Measuring oil temperature can be a
useful additional layer of protection. If the oil overheats, this is going
to negatively impact its viscosity, and the oil won't be capable of doing its
job, which can lead to engine failure. Now the ECU, by seeing the oil temperature,
can activate the limp home mode, or refuse to start the engine, before
oil temperature normalize again. In addition to relaying information to
the ECU, the oil temperature sensor can also relay information to engage,
or display visible to the driver. And then the driver can take preemptive action, and shut the engine down if
oil temperatures get too high. In order to be able to measure the temperatures of oil, the sensor must come into direct
contact with the oil inside the engine. As such it's often found on the engine
block, or less often on the cylinder head. In newer cars, it can be found
integrated into the oil level sensor. Depending on how it fails, a
malfunctioning oil temperature sensor might make the ECU think that
the oil temperatures are too high. Even though they aren't. And then the ECU might incorrectly
trigger a limp home mode. The sensor can also malfunction in a way that
it fails to report overly high oil temperatures, which can result in engine damage. A faulty oil temperature sensor is very easy
to spot, if there's a gauge or display for it. The O2 or the oxygen sensor measures the
amount of oxygen present in the exhaust gases. The amount of oxygen present in exhaust gases, directly corresponds to the amount of
fuel burned inside the combustion chamber. By measuring the oxygen, the oxygen
sensor can actually tell the ECU the air-fuel ratio at which the engine is running. Now, the air-fuel ratio, or the ratio of
air to fuel inside the combustion chamber, is absolutely critical for both
engine performance and emissions. And must be constantly monitored to
ensure that it is where it needs to be. We have two kinds of oxygen sensors. Narrowband and wideband. Narrowband sensors can tell if the
engine is running rich or lean. But they cannot tell exactly, how rich
or how lean the engine is running. On the other hand, the wide band sensor
covers a much wider range of air-fuel ratios. And you can tell the ECU exactly how
rich or lean the engine is running. Although it's small, the oxygen
sensor is a pretty complicated device. It involves zirconium bulbs, and
various platings and what not. And explaining it in this video would really
make the video too long and complicated. So, for the purposes of this video what I
will tell you, is that the amount of oxygen measured at the sensor tip, corresponds
to a voltage produced by the sensor. So for example, 0.5 volts is going
to be near the ideal air-fuel ratios. And at the other far ends of the spectrum,
we can find too rich and too lean. So what the ECU is going to do, it's going
to increase or decrease the amount of fuel injected, in order to reach again
the ideal air-fuel targeted ratio. Now, most catalytic converter equipped cars, are
going to have a minimum of two oxygen sensors. One is going to be before, and
one after the catalytic converter. The one before the catalytic converter
is called the upstream oxygen sensor, and it's usually going to be right at
the exhaust manifold, or right behind it. And it's used to see the exact air-fuel
ratio at which the engine is running. The one after the catalytic converter, that
sensor is called the downstream sensor. And it's used to verify that the catalytic
converter is properly doing its job. Failure symptoms can range from
barely noticeable, to very noticeable. But even if the symptoms are hard to notice, the
vehicle is likely going to fail an emissions test. Now, if it's noticeable, it's
going to be really noticeable. The engine is going to run rough Especially on more modern cars, which
rely more heavily on the oxygen sensor. More modern cars, can even refuse to start the
engine if the sensor has completely failed. If you know that you have a bad oxygen
sensor, then it's a really good idea to replace it as soon as possible,
even if the vehicle is running okay. Because an overly rich running condition,
can lead to your catalytic converter failing far more sooner than it needs to. Now, wide-band oxygen sensors are
also an absolutely critical tool for tuning performance and racing engines. And the AEM carries one of the most
popular, and the fastest responding, wideband setup on the market. Links are below. An EGT is an exhaust gas temperature sensor. And as the name reveals, it measures
the temperature of the exhaust gas. Now, an EGT is a probe that must be
present directly in the exhaust stream, in order to measure the
temperature of the exhaust gas. By measuring the temperature of the exhaust, we
can infer information about the air-fuel ratio. Because changes in the air-fuel ratio,
are also going to be directly correlated with changes in the exhaust gas temperature. Now, an EGT probe isn't often
used on gasoline engines. But it can be useful to protect the turbo, and
the catalytic converter from thermal overall. Now, EGT probes are often used on
turbo diesel and diesel engines to verify that the DPF(or diesel particular filter) has reached a sufficiently high temperature for regeneration. They're also useful for protecting the
SCR(or selective catalyst reduction) in LNT(or lean NOx trap)
and other NOx absorbing systems. Although it's considered an old tool when it
comes to tuning performance and racing engines, an EGT probe can still be a very
useful tool that provides valuable insight into what's happening inside the engine. Naturally, AEM has some very sleek
EGT setups, that you can check out. In order to get the most accurate
reading of exhaust gas temperatures, the EGT probe must be as close to
the exhaust valves as possible. This is why you're always going to find it in the
exhaust manifold very close to the cylinder head. The other location is always going to be after the DPF, or diesel particular filter,
to verify if the DPF is doing its job. EGT probes
are very rarely present from the factory gasoline engines, so really aren't any very
common symptoms to discuss. When it comes to diesel vehicles. An EGT failure is going to cause the vehicle
to go into regeneration mode very often. And regeneration mode is going
to last longer than usual. And you may also get poor
mileage and poor performance. Now, NOx are nitrogen oxide sensors. And they measure the amount of
nitrogen oxides in the exhaust gases. They're usually only present on diesel vehicles, and were briefly present on some stratified
charged gasoline engines in the past. Their main role is to verify the
correct operation of the SCR. Or the selective catalyst reduction system. This is an active emission
system in diesel vehicles, which injects ammonia or diesel emissions
fluid, directly into the exhaust gases. And this converts the nitrogen oxides into
nitrogen, water and minute amounts of CO2. There's usually two of these
sensors in a diesel vehicle One before, and one after the
selective catalyst reduction system. The one before, measures how
much much nitrogen is coming in. And the one after measures how
much nitrogen oxide is coming out, to make sure that the selective catalyst
reduction system is doing its job. A failure is going to trigger most modern
diesel vehicles to go into a "limp mode home". You also might get an erratic
idle, and poor mileage. Now 'knock' is abnormal
combustion inside the engine. If it's strong enough, and if it persists long
enough, it can cause catastrophic engine damage. A knock sensor is essentially a microphone. Tuned to listen to the specific
frequency of knock inside the engine. This depends on the engine, but largely it actually depends on
the bore and stroke of that engine. If the knock sensor detects knock, it's
going to relay this information to the ECU. And the ECU is going to respond, by
either retarding ignition timing, or increasing the amount of
fuel injected into the engine. To prevent the knock from occurring again. In order to be capable of hearing the knock
resonating throughout the engine block, the knock sensor is always
going to be on the engine block. Many engines with six or more cylinders have
two or even knock sensors in some cases. In many cases, a knock sensor's failure will have
zero effect on the way the engine is running. You might get a check engine light, but
the engine will run completely normal. Now, the scenario is a bit different on more
modern cars, whose ECU once it detects knock sensor failure, is going to often trigger a limp
home mode, until the knock sensor is replaced. And there you have it. All the sensors. Is it really all the sensors? Well, likely not Because the number of sensors on
modern engines is growing everyday. And by the time I was shooting this video,
somebody might have invented something new. So if I did miss a sensor, let me know. Also, if you want a more in-depth video on any of the sensors in this
video, tell me about that as well. So yeah, that's pretty much it for today. As always thanks a lot for watching. And I'll be seeing you soon,
with more fun and useful stuff. On the D4A channel.
