The MAP sensor on your 2.0L, 2.2L or 2.5L GM car or pickup 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).
Contents of this tutorial:
You can find this tutorial in Spanish here: Cómo Probar El Sensor MAP Con Multímetro (GM 2.2L) (at: autotecnico-online.com).
Symptoms Of A Bad MAP Sensor
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 check engine light will be shining nice and bright on your car's (or pickup's) instrument panel.
- If your 2.0L, 2.2L or 2.5L GM car or pickup is 1995 or newer it'll be OBD II equipped, so when the MAP sensor fails you'll see DTCs:
- P0106: MAP Sensor System Performance.
- P0107: MAP Sensor Circuit Low Voltage.
- P0108: MAP Sensor Circuit High Voltage.
- If your 2.0L, 2.2L or 2.5L GM car or pickup is 1994 or older (and thus not OBD II equipped), you'll see DTCs:
- 33: MAP Sensor Signal Voltage High.
- 34: MAP Sensor Signal Voltage Low.
- Your car (or pickup) won't start.
- The engine takes forever to start (extended cranking time) and when it finally does, it runs very rough.
- Black smoke coming out of the tailpipe along with really bad gas mileage.
- The engine idles rough when running and has a lack of power when accelerated.
MAP SENSOR TEST 1: Checking The MAP Signal With A Multimeter
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 above).
Remember, the MAP sensor must remain connected to its 3 wire connector.
Connect the black multimeter test lead directly to 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 step 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 vehicle. 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 sensor is bad. To test for power, go to: MAP TEST 2.