TEST 1: Verifying The MAP Sensor Has Power
The very first thing we'll do, to find out if the MAP sensor is bad and causing a P0108 DTC, is to make sure it's getting power.
The PCM supplies this power in the form of 5 Volts DC and we can easily test for these 5 Volts with a multimeter.
NOTE: This test can be done with the MAP sensor connected or disconnected to its electrical connector.
Alright, this is what you'll need to do:
- 1
Disconnect the MAP sensor from its electrical connector.
- 2
Place your multimeter in Volts DC mode.
If you don't have a multimeter or need to upgrade yours, check out my recommendation here: Abe's Multimeter Recommendation (at: easyautodiagnostics.com). - 3
With the red multimeter test lead, probe the wire that connects to the pin labeled with the number 1 in the image above.
NOTE: You should avoid probing the front of the connector with the multimeter's test lead or you'll damage the connector's metal terminal. Instead, use a back-probe on the connector or use a wire-piercing probe on the wire. - 4
Connect the multimeter's black test lead to the battery's negative post.
- 5
Turn the key to the ON position (but engine OFF).
- 6
Your multimeter should show you 4.5 to 5 Volts DC.
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. So far so good, since this is the correct and expected test result. The next step is to check that the MAP sensor is getting Ground. For the Ground test, go to: TEST 2: Verifying The MAP Sensor Has Ground.
CASE 2: The multimeter DID NOT register 5 Volts. Double check your connections and retest. If you still don't see the 5 Volts, then this test result 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 Honda vehicle.
TEST 2: Verifying The MAP Sensor Has Ground
So far, you've confirmed code P0108 (with your scan tool) and that the MAP sensor has power (5 Volts DC) in TEST 1.
In this test step, you're gonna' verify that the MAP sensor is getting Ground using your multimeter once again.
IMPORTANT: Remember, this Ground is provided directly by the PCM, so 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
Disconnect the MAP sensor from its electrical connector.
- 2
Place your multimeter in Volts DC mode.
- 3
Turn the key to the ON position but don't crank or start the engine.
- 4
With the black multimeter test lead probe the middle wire of the MAP sensor connector.
This is the wire that connects to the pin labeled with the number 2 of the MAP sensor (see the image above). - 5
Connect the multimeter's red test lead to the battery's positive (+) post.
- 6
Your multimeter should show 10 to 12 Volts DC.
OK, let's take a look at what your results mean:
CASE 1: The multimeter registered 10 to 12 Volts. This is the normal and correct test result and lets you know that the PCM is providing a good path to Ground for the MAP sensor.
The next step, and the last one, is see if the MAP sensor can react to the changes in air pressure while you apply (and release) vacuum to it. For this test go to: TEST 3: Bench Testing The MAP Sensor.
CASE 2: The multimeter DID NOT register 10 to 12 Volts. Double check your multimeter connections and repeat the test. If your multimeter still doesn't show 12 Volts, then the MAP is not fried and not the cause of the MAP sensor 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.
