MAF TEST 1: Power Circuit

Testing The VW Passat (98-99) Mass Air Flow (MAF) Sensor

All of the four MAF Tests that you're about to do, are done with a multimeter.

In this first, test, you'll make sure that the MAF Sensor in your Passat is getting power.

What I suggest you to do is to use a test probe that pierces thru' the wire's insulation (Wire Piercing Probe)... DO NOT insert anything into the female terminal.

Alright, this is what you'll need to do:

  1. 1

    Put the multimeter in VOLTS DC mode. This circuit can be tested with the MAF Sensor connected to its connector or not.

  2. 2

    With the red multimeter test lead and an appropriate tool, probe the wire identified with the number 3 in the photo.

  3. 3

    With the black multimeter test lead probe the battery negative (-) terminal. Turn Key On with the engine Off.

  4. 4

    You should see 12 Volts on the multimeter. Do you have 12 Volts?

Let's interpret your multimeter test results:

CASE 1: Your multimeter registered 12 Volts: This is good and tells you that the MAF sensor is getting power, the next step is to test one (of two) Ground Circuits. Go to MAF TEST 2.

CASE 2: Your multimeter DID NOT register 12 Volts: Recheck all of your multimeter connections and retest. If you still do not see these 12 Volts, then this exonarates the MAF Sensor as bad since without this voltage it's not gonna' work.

MAF TEST 2: Ground Circuit

Testing The VW Passat (98-99) Mass Air Flow (MAF) Sensor

In this test, you'll check the first of two Grounds that the MAF Sensor, on your Passat, needs to produce a signal.

This Ground is a power ground that grounds somewhere on the Engine or Chassis.

Alright, this is what you need to do:

  1. 1

    Put the multimeter in VOLTS DC mode. This circuit can also be tested with the connector connected to the MAF Sensor or not.

  2. 2

    With the black multimeter test lead and an appropriate tool, probe the wire identified with the letter number 1 in the photo.

  3. 3

    With the red multimeter test lead probe Battery Positive terminal.

  4. 4

    You should see 12 Volts on the multimeter. Do you have 12 Volts?

Let's interpret your multimeter test results:

CASE 1: Your multimeter registered 12 Volts: This tells you that this path to ground is OK, the next step is to make sure that the second Ground, the MAF has, also is OK, for this, go to MAF TEST 3.

CASE 2: Your multimeter DID NOT register 12 Volts: Recheck all of your multimeter connections and retest. If you still do not see these 12 Volts, then this exonarates the MAF Sensor as bad since without this ground it's not gonna' work.