TEST 1: MAP Sensor Voltage Signal Performance Test

How To Test The MAP Sensor (2.5L Dodge Dakota)

In this very first test, we're gonna' check the performance of the MAP sensor with a multimeter and a vacuum pump.

If you don't have a vacuum pump, don't sweat it. You can apply vacuum to the MAP sensor using a vacuum hose and the good ole' lungs.

To successfully diagnose the MAP sensor, you need to keep in mind is that as you apply vacuum to the MAP sensor its signal voltage should decrease. When you let go of the vacuum, this voltage should shoot back up to its original value.

You'll need a multimeter for this test, if you don't have a multimeter and need to buy one, check out my recommendations here: Buying A Digital Multimeter For Automotive Diagnostic Testing.

IMPORTANT: The MAP sensor needs to stay connected to its electrical connector for this test to work. You'll need to use a back-probe or a wire-piercing probe to measure the MAP signal voltage. To see what a wire-piercing probe looks like, go here: Wire Piercing Probe.

Let's get started:

  1. 1

    Connect your vacuum pump to the MAP sensor's vacuum inlet port. Reconnect the MAP sensor to its connector if you disconnected it.

  2. 2

    Set your multimeter's selector to Volts DC mode and with the red test lead, probe the DK GRN/RED wire of the MAP sensor's connector.

    Remember, the MAP sensor must remain connected to its 3 wire connector.

  3. 3

    Ground the BLACK multimeter test lead directly on the battery negative (-) terminal.

  4. 4

    When everything is ready, turn the Key on but don't start the engine. This will power up the MAP sensor and you should see a reading of 4.5 to 4.7 Volts DC on your multimeter.

    Now, apply vacuum to the MAP sensor with the vacuum pump (or your mouth). The voltage signal value should decrease.

    Release the vacuum. Once released, your multimeter should show the original voltage value.

    Repeat this test step several times making sure that each time the voltage decreases/increases as you apply/release vacuum.

Let's find out what your test results mean:

CASE 1: The MAP voltage signal decreased and increased as you applied and released vacuum. This is the correct and expected test result and lets you know that the MAP sensor on your 2.5L OHV Dodge Dakota is not defective.

CASE 2: The MAP voltage signal DID NOT increase (and/or decrease) as you applied and released vacuum. In most cases, this test result is enough to confirm that the MAP sensor is defective and that it needs to be replaced.

To be sure the MAP sensor is defective, you need to make sure it's getting power and ground. For the next MAP sensor diagnostic tests, go to: TEST 2: Verifying MAP Sensor Has 5 Volts and Ground.

CASE 3: Multimeter DID NOT register any voltage. In most cases, this test result is enough to confirm that the MAP sensor is defective and that it needs to be replaced.

To be sure the MAP sensor is defective, you need to make sure it's getting power and ground. For the next MAP sensor diagnostic tests, go to: TEST 2: Verifying MAP Sensor Has 5 Volts and Ground.

TEST 2: Verifying MAP Sensor Has 5 Volts And Ground

Verifying MAP Sensor Has 5 Volts and Ground. How To Test The MAP Sensor (1996, 1997, 1998, 1999 2.5L OHV Dodge Dakota)

Now that you have confirmed that a MAP sensor signal isn't decreasing as you apply vacuum (TEST 1), you need to make sure that it's getting power and ground.

Both of these are provided by your Dodge Dakota's fuel injection computer.

OK, for specifics: We're gonna' test the violet with white stripe (VIO/WHT) wire for 5 Volts. We're gonna makes sure that the black with light blue stripe (BLK/LT BLU) wire is providing ground.

IMPORTANT: When testing the ground wire of the MAP sensor connector, be careful not to short it to 12 volts (battery power) or you will fry your 2.5L Dodge Dakota's fuel injection computer.

Set your multimeter to Volts DC and:

  1. 1

    Verify that the VIO/WHT wire has voltage (4.5 to 5 Volts DC) with the key on but engine off.

    Connect the red multimeter test lead (using the appropriate tool) to the VIO/WHT wire. Connect the black multimeter test lead to the negative battery terminal.

    Your multimeter should read 4.5 to 5 Volts DC.

  2. 2

    Verify that the BLK/LT BLU wire has ground with the key on but engine off.

    Connect the black multimeter test lead (using the appropriate tool) to the BLK/LT BLU wire. Connect the red multimeter test lead to the positive battery terminal.

    Your multimeter should read 12 Volts DC.

Let's take a look at your test results:

CASE 1: The MAP sensor is getting power and ground. This is the correct and expected test result.

With this test result you can now conclude that the MAP sensor is defective and that it needs to be replaced. To be a bit more specific, you can reach this conclusion because you have confirmed that the MAP sensor is getting power and ground and yet it's not producing decreasing increasing voltage signal when you applied vacuum (in TEST 1).

CASE 2: The MAP sensor IS NOT getting power or ground. This test result tells you that the reason the map voltage signal did not react to the vacuum you applied (in TEST 1) is because it's missing power and/or ground.

The most common cause of this test result is a problem in the wiring between the MAP sensor connector and the fuel injection computer connector. Although it's beyond the scope of this tutorial to check the MAP sensor wiring, your next steps should be to check the continuity of the MAP sensor circuits between its connector and the fuel injection computer connector.