MAP SENSOR TEST 2: Checking The Power Circuit

How To Test The MAP Sensor With A Multimeter (Jeep 2.5L, 4.0L, 5.2L)

So far, in MAP TEST 1, you have verified that the MAP sensor on your Jeep SUV (Wrangle, Cherokee, Grand Cherokee) is not creating a signal or the signal is erratic

An so, in this MAP sensor test step, you're gonna' 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.

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. 1

    With your multimeter still in Volts DC mode from the previous test and the Key On (but engine Off).

  2. 2

    Probe the wire labeled with the number 1, in the image viewer, 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. 3

    Now Ground the black multimeter test lead on the battery's negative post.

  4. 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 reason the MAP sensor is not bad, since without these 5 Volts DC, the MAP sensor can not function.

MAP SENSOR TEST 3: Checking The Ground Circuit

How To Test The MAP Sensor With A Multimeter (Jeep 2.5L, 4.0L, 5.2L)

The next step (after verifying the MAP signal and power circuit) is to make sure that the MAP sensor on your Jeep SUV has a good path to Ground. So, in this test step, you're gonna' verify that the MAP sensor is getting Ground using your multimeter once again.

A word of caution: 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. 1

    With your multimeter still in Volts DC mode from the previous test and the Key On (but engine Off).

  2. 2

    Probe the wire labeled with the number 3 in the image viewer, 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. 3

    Now connect the red multimeter test lead on the battery's positive (+) post.

  4. 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 the normal result and it means that the MAP sensor your Jeep Grand Cherokee (Wrangler, Cherokee) 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, taken interpreted together, indicate that the MAP sensor is bad.

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.

Jeep Vehicles:

  • Cherokee 2.5L, 4.0L
    • 1987, 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995
  • Comanche 2.5L, 4.0L
    • 1987, 1988, 1989, 1990, 1991, 1992
  • Grand Cherokee 4.0L
    • 1993, 1994, 1995

Jeep Vehicles:

  • Wagoneer 2.5L, 4.0L
    • 1987, 1988, 1989, 1990
  • Wrangler 2.5L, 4.0L
    • 1986, 1987, 1989, 1990, 1991, 1992, 1993, 1994, 1995