MAP SENSOR TEST 2: Checking MAP Sensor Is Getting Power
If you've reached this point in your MAP sensor diagnostic, you have:
One: Verified that the check engine light is lit up because a MAP sensor trouble code is stored in the computer's memory.
Two: Verified that the MAP sensor on your 2.0L, 2.2L or 2.5L GM car or pickup is not creating a signal or the signal is erratic in TEST 1.
The next step and the purpose of this test section, is to verify that the MAP sensor is getting power, since without power it won't work. This power come in the form of 5 Volts and the PCM (Powertrain Control Module = Fuel Injection Computer) is the one that provides this juice.
NOTE: Since this circuit is directly connected to the PCM, be careful and don't short this wire to battery power (12 Volts), or you run the risk of frying the PCM.
Alright, this is what you'll need to do:
- 1
With your multimeter still in Volts DC mode from the previous test and the key ON (but engine OFF).
- 2
Probe the wire labeled with the number 1 in the image above, with the red multimeter test lead.
You can test for these 5 Volts with the MAP sensor's electrical connector connected to the MAP sensor or not, just avoid probing the front of the connector. - 3
Now Ground the black multimeter test lead on the battery's negative post.
- 4
Your multimeter should show you either:
1.) 5 Volts DC
2.) 0 Volts.
OK, now that the testing part is done, let's take a look at what your results mean:
CASE 1: The multimeter registered 5 Volts. This is the correct result and it's starting to look like the MAP sensor is bad but you still need to check that the MAP sensor is getting Ground. For the Ground test, go to: MAP SENSOR TEST 3.
CASE 2: The multimeter DID NOT register 5 Volts. This results lets you know that the MAP sensor is not bad, since without these 5 Volts DC, the MAP sensor can not function.
Although it's beyond the scope of this article to troubleshoot the cause of these missing 5 Volts, you have now eliminated the MAP sensor as bad. Resolving the issue that is keeping these 5 Volts from being supplied will solve the MAP sensor issue on your 2.0L, 2.2L or 2.5L GM car or pickup.
MAP SENSOR TEST 3: Checking MAP Sensor Is Getting Ground
So far your MAP sensor diagnostic has:
One: Confirmed a MAP sensor trouble code is stored in the computer's memory.
Two: Verified that the MAP sensor is not creating a voltage signal or the voltage signal is erratic in TEST 1.
Three: Verified that the MAP sensor is getting power TEST 2.
The next step is verify that the MAP sensor is getting Ground using your multimeter once again.
IMPORTANT: since this circuit is directly connected to the PCM, be very careful and don't short this wire to battery power (12 Volts), or you WILL FRY the PCM.
Alright, this is what you'll need to do:
- 1
With your multimeter still in Volts DC mode from the previous test and the key ON (but engine OFF).
- 2
Probe the wire labeled with the number 3 in the image above, with the black multimeter test lead.
It doesn't matter if you probe this circuit (wire) with the connector connected to the MAP sensor or not, but do not probe the front of the connector (if you decide to unplug the connector to test for this path to Ground). - 3
Now connect the red multimeter test lead on the battery's positive (+) post.
- 4
Your multimeter should show you either:
1.) 12 Volts DC
2.) 0 Volts.
OK, let's take a look at what your results mean:
CASE 1: The multimeter registered 12 Volts. This is the normal result and it means that the MAP sensor your 2.0L, 2.2L or 2.5L GM car or pickup is fried and needs to be replaced.
Here's why: In MAP TEST 1 and 2, you verified that the MAP sensor is not producing the correct values (when you applied vacuum) and that it does have power. Since in this test step you have confirmed that the MAP sensor does have a solid path to Ground, these results, interpreted together, indicate that the MAP sensor is bad.
If you'd like to save a few bucks on the MAP sensor, take a look at the section: Where To Buy The MAP Sensor And Save.
CASE 2: The multimeter DID NOT register 12 Volts. Double check your multimeter connections and repeat the test. If your multimeter results still do not indicate 12 Volts, then the MAP is not fried and not the cause of the MAP diagnostic trouble code (DTC) issue.
Here's why: Without a good path to Ground, that the PCM provides internally, the MAP sensor will not work. With this test result, you have eliminated the MAP sensor as bad.
