Testing The 1998-1999 VW Passat Mass Air Flow (MAF) Sensor

VW used several types of mass air flow sensors, for the most part they can be divided into two categories. One type has 4 male spade terminals and the other has 5 male spade terminals. This test tutorial is for the one with the 4 male spade terminals.

The most common symptoms of a bad MAF sensor are:

  1. A MAF sensor code.
  2. Lean and/or Rich code(s).
  3. Fuel Trim code(s).
  4. A tremendous lack of power upon acceleration.
  5. Black smoke coming from the tail-pipe.
  6. Vehicle may idle rough and stall.

The mass air flow test is a very easy and simple test but there are a couple of things that have to be done first.

The most important thing to do first, is to make sure your MAF sensor isn't contaminated with dirt and/or oil, since the tests in this article assume the MAF sensor isn't contaminated. Why? Because this MAF sensor is a hot-film type that easily becomes contaminated with dirt and stuff from the air filter not performing its job. Cleaning this type of sensor can be difficult since the heat-film is not clearly visible to the eye but it can be cleaned.

This contamination will cause the sensor to produce a lower reading to the ECM (Engine Control Module = Fuel Injection Computer). The most common symptom of this contamination is a hesitation or a time-lag in engine responce that is felt after the accelerator pedal is depressed. As stated in the list at the beginning of this article, other symptoms may include but are not limited to: higher tailpipe emissions and diagnostic codes that may illuminate the "Check Engine" light.

If cleaning the MAF sensor, use an electronics spray cleaner to do it with. This in itself may solve your problem. Don't use carb or brake clean spray. These solvents can damage the sensor. Also, don't attempt to physically clean the sensor with anything. Check your local auto parts store, they will have MAF sensor cleaning spray.

After having checked for contamination the other things that you must check for (and eliminate if present) are:

  1. That the engine does not have any vacuum leaks.
  2. That there are no ignition system misfires. A misfire condition will skew the results of the test you'll perform here.

If the above conditions exist, repairing them first will more than likely solve your vehicle's drive-ability issue without having to test the MAF sensor, if not continue with the MAF Test in this article.