In this video, we're gonna be talking about manifold air pressure sensors or better known
as MAP sensors, and how to diagnose them.
When you're checking with a scan tool when you have the key on before you actually start
the vehicle, you wanna check the manifold absolute pressure sensor.
You wanna see what that reading is.
Now, some vehicles have a barometric pressure sensor.
Those are the same sensors, same types of sensors.
And those readings should be identical or very close to identical.
Now, that's basically measuring the barometric pressure in the air.
Now, that's gonna change with altitude.
If you go high up on a mountain, that number is gonna change, and that should change with
the manifold absolute pressure sensor.
And once I start the vehicle, this number will change and that number should stay the
same.
At this point, the vehicle is that idle.
That's the pressure that I have right now and I'm just gonna accelerate the throttle
to show you that it changes.
And then when the throttle closes real quick, the vacuum is gonna go down, and then it's
gonna go up real quick and then stabilize again.
That's how it should look.
So, as we graph this, if we look at this, the units are only going up and down by so
much.
And that's good.
If you saw a sudden spike, obviously I accelerated right there, but if you were at an idle and
you saw a spike like that going up or going down, then it would be an issue with the sensor
intermittently not working properly.
All right.
So, this is what I bad MAP sensor would look like.
If you compare this reading to the barometric pressure sensor, it's significant difference
and there happens to be an open circuit with this.
So, that's when we're gonna go check the wires and make sure we have all the wires and all
the connections are good.
You can see with the vehicle running, this sensor is not doing anything, which it should
do something.
Staying at the same voltage or that same reading isn't good.
The MAP sensor is located right here on this vehicle.
Most of the time when you're looking at the intake, you can see it's somewhere attached
to the intake and the connectors in the back right here.
There's three wires on this MAP sensor.
Just check those wires.
You can wiggle them while you're looking at some of the values to see if they change.
Disconnect the connector.
Just look for any corrosion in the connector.
Everything looks good there.
So, now we're gonna check these circuits, but we need to know what they are and what
they do.
This gray wire right here is a five-volt signal that's coming from the PCM.
Computer sends the five-volt signal out here.
And then there's a little reference signal right here, this orange wire, orange and black.
And what the low reference signal is, is basically the ground.
It's grounded through the PCM.
And the wire in the middle is the actual signal that the MAP sensor should send to the PCM
saying what the pressure is, whether it's higher or low.
Right.
So, to test this, I'm gonna use a multi-meter and bolt meter.
You don't wanna use a test light because it's only a five-volt circuit and it's not gonna
light up the test light or depending on your test light, it probably won't light it up.
Now, I'm gonna put one lead on a ground and the other lead, I'm gonna test the terminals.
Now, you wanna make sure you don't push into the terminals, you just touch them lightly.
And on the voltage scale, I'm looking for five volts right there.
And if you look at the meter, I do have five volts.
Now, if you had 12 volts there, that would not be good or anything significantly above
five volts.
But based on our code that we have in a low voltage code, there shouldn't be higher voltage
there.
So, that's good.
To test the ground circuit, I'm actually gonna test in between those two terminals, the low
reference terminal and then the five-volt reference and just make sure I have five volts
again.
And I do.
So, that's just basically making sure the computer is grounding that properly.
So, I'm gonna use a jumper harness that has a fuse in it, and it's just two wires.
And we wanna jump the green wire and the gray wire.
So, this is the five volts.
So, that's gonna send five volts down the signal wire.
So, that's what we should see on the scan tool.
So, I'm just gonna lightly touch the terminals.
If you have the proper leads, you can actually plug them in just like that, then you can
watch it.
And it goes up to five volts, which is good.
Disconnect it, connect it again.
Perfect.
So, we know our wires are good and our connector is good.
So, that would mean that the MAP sensor is bad.
So, I hope this video helped you understand how simple a MAP sensor circuit is and how
to diagnose it.
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