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 Test’ doesn't diagnose all the possible MAF malfunctions. Well, then, this is the article for you. (Click here for the 4 wire VW Bosch MAF Sensor Test)
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 slots for only 4 male spade terminals and the other has 5 slots for 5 or 4 male spade terminals. This tutorial is for the MAF sensor with the connector that has 5 slots for 5 or 4 male spade terminals. You'll need to unplug the MAF on your VW to make sure, since some MAF sensors with 5 male spade terminals only have four wires coming out of the connector. You can see an example of this here: MAF Sensor With 5 Slot Connector With 4 Wires.
Another important note is that this article only tests the older analog type Bosch MAF sensor (Air Flow Meter). By this I mean that the newer VW cars and minivans are using a Frequency based MAF whose MAF Signal is a digital signal that can only be measured using a multimeter with frequency Hertz capability. The test in this article is for the Bosch MAF sensor that produces an analog voltage signal that can be measured by setting the Voltmeter in Volts DC mode.
Symptoms Of A Bad VW MAF
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:
- The car will not idle or idle rough.
- Black smoke coming from the tail-pipe.
- 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.
- A MAF sensor code. But not always. I have replaced fried MAF sensors on different VW's that never set a MAF code.
- Lean and/or Rich code(s).
- Fuel Trim code(s).
- Bad gas mileage.
Is My MAF 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:
- I'll test it first following the guidelines set in this article, to see if it's producing a MAF Signal.
- 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.
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.
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 RPM's that at an idle of 900RPM's the voltage output will be greater at 2500 RPM's 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 (RPM's) 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.
TEST INFO: A Description Of The Circuits
The safest way to test these circuits, and the method I always use, is using a wire piercing probe. You can see an example of this tool here: Wire Piercing Probe. Using this probe, I don't have to disconnect the MAF sensor's connector to probe the front of the female terminal and possibly risk damaging it.
Independent of the method you use, be careful not to damage the wire or the female terminal. Take all safety precautions.
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.
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.
- Number 5
- MAF Signal
- Number 4
- 5 Volt Reference from ECM.
- Number 3
- Ground. Provided by the ECM internally.
- Number 2
- 12 Volt battery power.
- Number 1
- Air Temp Sensor Circuit. This slot may be empty or not on your MAF sensor.
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.
We're ready to get started...
VW Vehicles That Use This MAF Sensor
Not a complete list, but will give you a general idea of what vehicles do use it.
- 1998, 1999, 2000, 2001, 2002, 2003
- 1999, 2000, 2001