Testing the GM manifold absolute pressure (MAP) sensor on your GM 2.8L, 3.1L, or 3.4L V6 equipped car can be accurately done using only a multimeter and a vacuum pump.
This article will show you how to bench test it (although you'll be leaving the MAP sensor connected to its electrical connector) to be able to either condemn the MAP as BAD or eliminate it as the source of the diagnostic trouble code or drive-ability issue your car or mini-van is going through.
Now, if your driving a post 1995 ODB II GM vehicle and you have a MAP sensor problem 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 your driving a pre-1995 vehicle with OBD I and you have a MAP sensor issue, 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:
The two most obvious symptoms of a bad MAP sensor is that the check engine light will be shining nice and bright and that the engine in your vehicle will idle very rough.
These are some of the other symptoms your GM 2.8L, 3.1L, or 3.4L car or mini-van will experience with a BAD MAP sensor:
The MAP sensor's job is to measure the amount of vacuum in the intake manifold. This vacuum measurement is converted into a DC voltage signal that can be easily tested with a multimeter in Volts DC mode.
So, this first test will have you checking to see if the MAP is able to produce a valid MAP signal as you apply vacuum to it with a vacuum pump. This test will give you three possible test results and at the bottom of the test steps I've included how to interpret them.
NOTE: You don't have to use a vacuum pump to test the MAP sensor. You can use your mouth to apply vacuum to the MAP sensor (via a vacuum hose). The difference will be that with applying vacuum with your mouth you won't be able to bring down the voltage to 1.1 Volts. The important thing is just to see the voltage go down and then go back up (to its original value) when you apply vacuum with the ‘good ole' lungs’.
OK, to get this show on the road, this is what you need to do:
Disconnect the MAP sensor from its vacuum hose. On your specific vehicle, you may have to physically remove the MAP sensor from its mounting to disconnect it from its vacuum hose.
Connect your vacuum pump to the MAP sensor's vacuum nipple. If you had to disconnect the MAP sensor from its electrical connector to remove it, reconnect it to it now.
With your multimeter in Volts DC mode probe the wire labeled with the 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.
Turn the Key on but don't start the engine. At this point your multimeter should register 4.7 Volts DC.
Now, pump the vacuum pump to apply vacuum to the MAP sensor. The multimeter should register the following voltages at the following vacuum values (they may differ a little on your specific 2.8L, 3.1L, 3.4L GM car or mini-van):
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.
Repeat this test step several times and each time, you should see the same values on your multimeter.
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 on your instrument cluster.. take a look at the section: MAP Code Won't Go Away for more info.
CASE 2: Your multimeter register 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.
“I bought a perfect second car... a tow truck.”