TEST 1: Checking For The MAP Sensor Signal

How To Test MAP Sensor (1997-2003 Jeep 4.0L)

In this first test, we'll check that the MAP sensor on your 4.0L equipped Jeep Cherokee (Grand Cherokee, Wrangler) is producing a signal when vacuum is applied to its vacuum port.

The middle wire, of the MAP sensor's engine harness connector, is the one that carries the MAP signal (to the PCM) and it's this wire that you'll need to tap into with your multimeter.

NOTE: Although the instructions assume you're using a vacuum pump, if you don't have one, you can use your mouth and a vacuum hose to apply vacuum to the MAP sensor's vacuum port.

OK, this is what we'll do:

  1. 1

    Remove the MAP sensor from the intake manifold (if you need to gain access to its vacuum port).

    Once you have removed it, reconnect it back to its electrical connector.

  2. 2

    Select Volts DC on your multimeter.

  3. 3

    Probe the middle wire of the MAP sensor with the red multimeter test lead.

    This is the wire that connects to the MAP sensor engine harness connector's terminal labeled with the number 2 in the illustration above.

    The best way to get to the signal inside the wire is using a wire piercing probe (to see what this tool looks like, click here: Wire-Piercing Probe).

  4. 4

    Ground the black multimeter test lead on the battery's negative (-) terminal.

  5. 5

    Connect your vacuum pump to the MAP sensor.

  6. 6

    Turn the key to the ON position (don't start the engine).

  7. 7

    Your multimeter should display: 4.8 V (this is no vacuum applied to the MAP sensor).

  8. 8

    Apply vacuum. As you apply vacuum, your multimeter should read:

    1.  5 in Hg - 3.9V.
    2. 10 in Hg - 3.1V.
    3. 15 in Hg - 2.1V.

NOTE: What you're looking for, as you apply and release vacuum is for the multimeter to show a decrease in voltage (as you apply vacuum) and an increase in the voltage back to 4.5+ Volts (as you release vacuum).

Let's interpret your test results:

CASE 1: The MAP sensor's voltage decreased/increased as you applied/released vacuum. This tells you that the MAP sensor is OK and not the true cause of the MAP sensor codes.

This also confirms that the MAP sensor is getting power (5 Volts) on wire and Ground.

CASE 2: The MAP sensor's voltage DID NOT decrease/increase as you applied/released vacuum. This usually means that the MAP sensor is bad but we'll need to make sure that the MAP sensor is getting both power and Ground.

For this test, go to: TEST 2: Checking That The MAP Sensor Is Getting Power.

TEST 2: Checking That The MAP Sensor Is Getting Power

How To Test MAP Sensor (1997-2003 Jeep 4.0L)

In TEST 1 you confirmed that the MAP sensor is NOT creating a signal when you applied vacuum to its vacuum port.

So the next steps, before condemning it as bad, is to make sure that your Jeep's PCM is feeding it with power (5 Volts) and Ground.

These 5 Volts are fed to the MAP sensor thru' the wire that connects to sensor's harness connector terminal labeled with the number 3 in the illustration above.

NOTE: You can check for these 5 Volts with the MAP sensor connected or disconnected from its harness connector.

This is what you'll need to do:

  1. 1

    Place your multimeter in Volts DC mode.

  2. 2

    Disconnect the MAP sensor from its electrical connector.

  3. 3

    With the red multimeter test lead probe the wire that connects to the terminal labeled with the number 3.

    Avoid probing the front of the connector to avoid damaging the female metal terminal.

    The best way to get to the signal inside the wire is using a wire piercing probe (to see what this tool looks like, click here: Wire-Piercing Probe).

  4. 4

    Connect the black multimeter test lead directly on the battery's negative (-) terminal.

  5. 5

    Turn the key to the ON position (but don't start the engine).

  6. 6

    Your multimeter should read 4.5 to 5 Volts DC.

Let's take a look at your test results:

CASE 1: 4.5 to 5 Volts are present. So far so good, since this means that the PCM is supplying power to the manifold absolute pressure (MAP) sensor.

The next step is to make sure that the PCM is feeding your Jeep's MAP sensor with Ground. For this test, go to: TEST 3: Verifying The MAP Sensor Is Getting Ground.

CASE 2: 4.5 to 5 Volts ARE NOT present. Recheck your multimeter connections and retest.

If after checking all of your multimeter connections and making sure the key is in the ON position AND your multimeter does not register the 4.5 to 5 Volts DC, then you've found the reason for the MAP sensor code/failure.

Without power in this circuit, the MAP sensor will not work. Now, it's beyond the scope of this article to test for this missing Voltage, but the most likely cause will be an ‘open’ or a short between the PCM connector and the MAP sensor connector.

Jeep Vehicles:

  • Cherokee 4.0L
    • 1997, 1998, 1999, 2000, 2001
  • Grand Cherokee 4.0L
    • 1997, 1998, 1999, 2000, 2001, 2002, 2003
  • Wrangler 4.0L
    • 1997, 1998, 1999, 2000, 2001, 2002