The MAP sensor on your 2.0L, 2.2L or 2.5L GM car or pick up is a three wire sensor that you can easily and very accurately test with only a multimeter.
This article will show you how to do it and in the process, you'll be able to say that ‘Yes, the MAP sensor is BAD and the cause of the problem’ or ‘No, the MAP sensor is OK and I have to keep looking for the problem elsewhere’.
If your specific GM vehicle is a 1995+ and OBD II equipped and a MAP sensor problem is lighting up the check engine light (CEL), you'll see one of the following codes: P0106, P0107, P0108 lighting up the check engine light (CEL) on the car's instrument cluster.
If it's a pre-1995 vehicle with OBD I and you have a MAP sensor problem, the check engine light will be lit by the following diagnostic trouble code: 33 (Manifold Absolute Pressure Sensor Circuit High Signal) or 34 (Manifold Absolute Pressure Sensor Circuit Low Signal).
To help you navigate this article a little easier, here are its contents at a quick glance:
Since the fuel injection system on your 2.0L, 2.2L or 2.5L GM equipped vehicle is a speed density system... the MAP sensor is one of the most important sensors the fuel injection computer needs to keep the engine running optimally.
When the MAP sensor fails, you'll see/feel one or more of the following symptoms of a BAD MAP sensor:
The very first thing that you'll do, to get this show on the road, is to test the MAP voltage signal that the MAP sensor creates.
You'll do this with a multimeter in Volts DC mode and with the engine off. As a matter o' fact, the entire test is done with the engine off even tho' the MAP sensor will be connected to its electrical connector.
NOTE: By the way... the test calls for a vacuum pump to be used, and although this is the best way to get an accurate test result... you can substitute your lungs/mouth for one if you don't have access to a vacuum pump.
OK, to get this show on the road, this is what you need to do:
Remove the MAP sensor from the Intake Manifold (if it's bolted directly onto the Intake Manifold).
Connect your vacuum pump to the MAP sensor's vacuum nipple. You probably had to disconnect the MAP sensor from its electrical connector to remove it, so if you did.. reconnect it to it now.
Set your multimeter's selector to Volts DC mode and probe the wire labeled with number 2 (in the image viewer).
Remember, the MAP sensor must remain connected to its 3 wire connector.
Ground the BLACK multimeter test lead directly on the battery negative terminal.
When everything is ready, turn the Key on but don't start the engine. This will power up the MAP sensor and you should see a reading of 4.7 Volts DC on your multimeter.
Now, apply vacuum to the MAP sensor with the vacuum pump (or your mouth). The multimeter should display the following DC voltages at the following vacuum values if your using a vacuum pump:
1.) 0 in. Hg ...... 4.7 Volts.
2.) 5 in. Hg ...... 3.9 Volts.
3.) 10 in. Hg .... 3.0 Volts.
4.) 20 in. Hg .... 1.1 Volts.
NOTE: If your applying vacuum with the good ole' lungs, you should see a smooth increase and decrease (without any gaps or skips) on the multimeter. I mention this because lung power alone won't be able to bring the voltage down to 1.1 volts but you will see the voltage decrease and increase as you apply and release vacuum.
Repeat this test steps 1 thru' 5 several times to make sure of your test results.
OK, let's take a look at what your vacuum pump test results mean:
CASE 1: Your multimeter registered the indicated voltages as you applied vacuum: This means that the manifold absolute pressure (MAP) sensor is good and not the cause of the MAP sensor code or problem on your GM 2.8L, 3.1L, or 3.4L car or mini-van. No further testing is required.
Now, if your vehicle still has the MAP sensor code lighting up the check engine light on your instrument cluster.. take a look at the section: MAP Code Won't Go Away for more info.
CASE 2: Your multimeter registered voltage, BUT it did not increase or decrease as you applied vacuum: This confirms that the manifold absolute pressure (MAP) sensor on your GM car or mini-van is BAD. Replacing the MAP sensor will solve the MAP code issue (P0106, P0107, P0108 or 33, 34)
CASE 3: Your multimeter registered 0 Volts: This usually means that the MAP sensor is fried. To be absolutely sure, I suggest confirming that the MAP sensor has power and ground. If both (power and ground) are present, the MAP is BAD. To test for power, go to MAP TEST 2.
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