TEST 1: Checking For Power

Making Sure The PWM Relay Is Getting Power. Jeep PWM Fan Relay Test Troubleshooting An Overheating Condition

IMPORTANT: Before you start this test, on your 1999-2004 Jeep Grand Cherokee, you need to have calculated the amperage the fan motor is consuming. This is very important.

So if you haven't, you can find the out how to do this here: FAN RELAY TEST 4 and Real Life Case Study. Once you've calculated the amperage draw (and it's within specification), come back to this test step.

OK, to get this show on the road, the first thing you'll do is to make sure the PWM fan relay is getting power.

These are the test steps:

  1. 1

    Disconnect the PWM fan relay from its electrical connector.

  2. 2

    Grab your multimeter and select Volts DC mode on it.

  3. 3

    Probe the gray (GRY) wire labeled by the number 1 (in the photo above) with the red multimeter test lead.

    What I recommend you do is to use a back-probe on the connector or a wire piercing probe on the wire. If you probe the front of the connector, do it very gently and with the appropriate size probe to avoid damaging the female terminal.

    NOTE: To access the PWM fan relay, you'll need to remove the front bumper.

  4. 4

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

  5. 5

    Your multimeter should register 10 to 12 Volts since the GRY wire is always hot.

OK, let's interpret your test results:

CASE 1: Your multimeter registered 10 to 12 Volts. This confirms that the fuse that supplies the PWM fan relay with power is not blown. You can proceed to the next test, go to: FAN RELAY TEST 2

CASE 2: Your multimeter DID NOT register 10 to 12 Volts. This confirms that the fuse that supplies the PWM fan relay is blown. Replace the fuse and retest.

This fuse is found in the fuse box in the engine compartment.

FAN RELAY TEST 2: Checking For Ground

Making Sure The PWM Relay Is Getting Ground. Jeep PWM Fan Relay Test Troubleshooting An Overheating Condition

In FAN RELAY TEST 1, you verified that the Pulse Width Modulated (PWM) Relay is getting power in the form of 12 Volts DC. In this test step, you're gonna' verify that the relay has a good Ground.

The wire that feeds Ground to the PWM fan relay is the black (BLK) wire labeled with the number 4 in the photo above.

We'll do a simple multimeter voltage test to test for the presence of Ground.

This is what you'll need to do:

  1. 1

    Disconnect the PWM fan relay from its electrical connector.

  2. 2

    Set your multimeter to Volts mode.

  3. 3

    Probe the black (BLK) wire of the connector with the black multimeter test lead.

    This is the wire connects to the female terminal labeled with the number 4 in the photo above.

    Use a back-probe on the connector or a wire piercing probe on the wire. If you probe the front of the connector, do it very gently and with the appropriate size probe to avoid damaging the female terminal.

  4. 4

    Connect the red multimeter test lead on the battery positive (+) terminal.

  5. 5

    Your multimeter should read 10 to 12 Volts if Ground is present in the wire.

OK, now that the testing part is done, let's take a look at what your results mean:

CASE 1: Your multimeter registered 10 to 12 Volts. This means that the PWM fan relay has a good path to Ground.

So far you have verified that the PWM Relay is receiving power and Ground, the next step is to test that your Jeep's fuel injection computer (technically known as the Powertrain Control Module= PCM) is actually activating the Pulse Width Modulated (PWM) fan relay.

This test will let you know if the PWM fan relay is OK or fried. Go to: FAN RELAY TEST 3.

CASE 2: Your multimeter DID NOT register 10 to 12 Volts. This test result indicates that the PWM fan relay does not have a good path to Ground.

This is very unusual, what I suggest you do is to splice a wire into this circuit which you should connect directly on the battery negative (-) terminal (without cutting it) and retest.

Jeep Vehicles:

  • Grand Cherokee 4.0L
    • 1999,
      2000,
      2001,
      2002,
      2003