VW Mass Air Flow (MAF) Sensor Test (5 Wire Type)

The most common way to test the 5 wire VW Mass Air Flow (MAF) sensor is just to unplug it with the engine running. If the MAF is bad (either because it's not producing a signal or producing an erratic one), the car's idle will return to normal and the car will seem to run fine.

But if you're like me, you want a more solid test, something that you can sink your teeth into, such as a test that involves a multimeter since the 'unplug the MAF sensor test' doesn't diagnose all the possible MAF malfunctions. If so, this is the tutorial for you.

NOTE: Before I go on, let me tell you that VW uses several types of mass air flow sensors (also known as Air Flow Meters), for the most part they can be divided into two categories.

• One type has a connector with 4 wires coming out of it.
  • 4 wire VW Bosch MAF Sensor Test: Testing The MAF Sensor (1998-1999 VW Passat).
• The other has a connector with 5 slots and may have 5 or 4 wires coming out of it.

This tutorial is for the MAF sensor with the connector that has 5 slots for 5 or 4 wires. In the photo above, the MAF sensor has a 5 slot connector with 5 wires. You can see the 5 slot connector with 4 wires here: MAF Sensor With 5 Slot Connector With 4 Wires.

Another important note is that this tutorial only tests the older analog type Bosch MAF sensor (Air Flow Meter) that produces an analog voltage signal (that can be read with a simple multimeter). To be a bit more specific: Newer VW cars and minivans are using a frequency based MAF sensor whose MAF signal is a digital signal that can only be measured using a multimeter with frequency Hertz capability or an oscilloscope.

APPLIES TO: This tutorial applies to the following vehicles:

• VW Beetle: 1998, 1999, 2000, 2001, 2002, 2003
• VW Jetta: 1999, 2000, 2001

Symptoms Of A Bad MAF Sensor

Your VW car can display any number of different symptoms when the Air Flow Meter (MAF sensor) goes bad but, the most common ones are:

1. The car will not idle or idle rough.
2. Black smoke coming from the tail-pipe.
3. A tremendous lack of power upon acceleration. In other words, you can start the car, but when you press the accelerator pedal, the car just won't move.
4. A MAF sensor code. But not always. I have replaced fried MAF sensors on different VW's that never set a MAF code.
5. Lean and/or Rich code(s).
6. Fuel Trim code(s).
7. Bad gas mileage.

Is My MAF Sensor Just Dirty?

It seems to me that the most common fix, in my experience, to solve a MAF issue on a VW has been to just clean it. Of course, you have to keep in mind that a dirty VW MAF sensor will not cause a lot of havoc. What I mean is that the worst complaints are usually bad gas mileage and/or a slight lack of power. So how do I diagnose a dirty/contaminated VW MAF sensor? Well:

1. I'll test it first following the guidelines set in this article, to see if it's producing a MAF Signal.
2. If it is producing a signal, but the signal's response is too slow to changes in Throttle Position, then I know to look into cleaning it.

Why does it get dirty/contaminated? Well, this MAF sensor easily becomes contaminated with dirt and stuff from the air filter not performing its job or the box that holds the air filter is broken or not sealing correctly. Cleaning this type of sensor can be a little difficult since this Sensor does not use ‘Hot Wires’ but a 'heat-film' that really isn't clearly visible to the eye (but it can be cleaned). Although I don't have step by step instruction on how to clean it, Googling the subject will bring you a lot of good articles on the subject.

As a last note on the subject, don't use carburetor or brake clean spray or gasoline to clean your MAF sensor with. These solvents can damage the sensor. Also, don't attempt to physically clean the sensor with anything. Your local auto parts store will have a MAF sensor cleaning spray.

Air Leaks

The second most common problem I have encountered on most VW's over the years is air leaks between the MAF sensor and the Throttle Body (especially true if it's a turbo-charged engine where the plumbing between the MAF sensor and Throttle Body seems to run for miles). It is crucial, yes very critical that you first check that there are no air leaks between these two. Otherwise this air leak will skew the results of your test and you might end up replacing a good MAF and in the process throwing money away.

How do you check for air leaks? With your eyes and hands. That's right, no special tools required. Just eyeball and physically shake/move the ducting to see if it's loose or disconnected.

MAF Sensor Test Essentials

OK, you're gonna' start by checking the basics. These are 12 Volts and battery Ground to the MAF sensor. After that, we'll test the actual performance of the MAF sensor as the engine is running. Use a digital multimeter for all tests where a multimeter is called for.

The MAF sensor produces an analog voltage signal. This MAF Signal's DC Voltage is directly related to amount of air the engine is breathing. Therefore, if the engine is breathing in more air at 2500 RPMs that at an idle of 900RPMs the voltage output will be greater at 2500 RPMs than at idle.

Now, when testing this voltage signal, the important thing to know is not an actual Volts number at a specific RPM, but to look for crazy and extreme fluctuations in the voltage signal that do not correspond to the actual air intake (RPMs) of the engine or no Signal at all. For example: If at Idle the voltage reading starts to spike up and down without you accelerating the engine or if there's no Signal at all.

In the TEST 4 section of this article, I'll show how you'll use a base voltage reading at idle from the MAF sensor that will help you to confirm that the MAF sensor is bad or not.

MAF Sensor Circuit Descriptions

The MAF connector has slots for 5 wires. On some vehicles, only 4 slots are actually used and the fifth one is empty. This is no cause for concern because it's the same sensor type regardless of the amount of circuits used. The testing information in this Fast Test Article applies to them all.

As you've already noticed, the photo (above) has the MAF connector numbered 1 thru' 5. I'll be using these numbers for the circuit descriptions. The sensor itself will have these numbers molded on it too. The large arrow represents the direction of the Air Flow into the engine. Here's the description of each circuit below.

MAF Sensor Circuits
Wire	Description
1	Intake Air Temp (IAT) Sensor (may be empty or not)
2	12 Volts DC
3	Sensor Ground (provided by ECM)
4	5 Volts Reference (provided by ECM)
5	MAF Signal (output)

What about the color of the wires? Good question. The colors of the wires in the photo will not match what is on your vehicle. This is no cause for concern. The circuit descriptions are not tied to the color of the wire. In other words, no matter what the color of the wire, the circuit descriptions remain the same.

IMPORTANT: All of the tests are ON CAR TESTS, do not remove or disconnect the mass air flow sensor from the vehicle or from its plumbing.

TEST 1: Making Sure The MAF Sensor Is Getting 12 Volts

The very first thing that we'll do is check that the MAF sensor is receiving 10 to 12 Volts.

The wire that delivers this voltage to the MAF sensor is the one I've labeled with the number 2 in the photo above.

IMPORTANT: Be careful not to damage the connector's female terminals with the multimeter test lead.

Alright, these are the test steps:

1. 1

   Disconnect the MAF sensor from its connector.

2. 2

   Put the multimeter in Volts DC mode.

3. 3

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

4. 4

   Gently probe the terminal of the connector that connects to the wire identified with the number 2 with the red multimeter test lead.

5. 5

   Turn the key ON but don't crank or start the engine.

6. 6

   You should see 10 to 12 Volts on the multimeter.

Let's examine what your test result means:

CASE 1: Your multimeter registered 10 to 12 Volts This confirms that the MAF sensor is getting power.

The next thing we need to check is that the MAF sensor is getting Ground. Go to: TEST 2: Making Sure The MAF Sensor Is Getting Ground.

CASE 2: Your multimeter DID NOT register 10 to 12 Volts. Recheck all of your connections and repeat the test.

If still no power, then resolving this lack of 12 Volts will solve the MAF sensor issue.