MAF SENSOR TEST BASICS
Testing the GM MAF sensor (early type) is a very simple and straightforward process that can be accomplished in three easy test steps. These are:
- Step One
- Verifying that the MAF sensor is receiving 12 Volts.
- Step Two
- Verifying that the MAF is receiving a good Ground.
- Step Three
- Testing and verifying the MAF signal that the mass air flow sensor produces as the engine is running.
Why A Multimeter That Can Read Hertz Frequency?
As stated in the page before, you'll need a digital multimeter for all tests where a multimeter is called for.
This multimeter must be able to read Frequency Hertz (Hz) (don't have a digital multimeter that can read Hertz frequency? Click here to see my recommendations: Buying A Digital Multimeter For Automotive Diagnostic Testing). Why? -you may ask. Well, it's because the output signal of the MAF sensor is a Hertz (Hz) frequency signal to the ECM.
This Hertz frequency signal is directly related to amount of air the engine is breathing. Common sense tells us that the engine will breathe in more air at 2500 RPMs than at an idle of 900 RPMs.So keeping this in mind, the Hertz value on the multimeter will be greater at 2500 RPMs than at 900 RPMs.
Now, when testing this Hz frequency signal, the important thing to know is not an actual Hz frequency number at a specific RPM, but to look for crazy and extreme fluctuations in the Hz frequency signal that do not correspond to the actual air intake (RPMs) of the engine. For example: If at Idle the Hertz reading starts to spike up and down without you accelerating the engine. Or, no Hertz reading at all.
In the TEST 3 section of this article, I'll show how you'll use a base Hz reading at idle from the MAF sensor that will help you to confirm that the MAF sensor is bad or not.
If you have access to an oscilloscope, I have included a scope waveform of what this MAF Signal should look like (in TEST 3). Whether you use a multimeter or an oscilloscope, you'll be able to successfully diagnose this mass air flow sensor.
Lastly, these tests are not designed to diagnose an intermittent problem with the MAF sensor. They are designed to diagnose a hard fault with the sensor.
MAF Sensor Circuit Descriptions
You'll notice that the photo (above) has the MAF connector lettered A thru C (If you look closely at the MAF sensor connector, you'll see these letters on it too). I'll be using these letters for the circuit descriptions. Here's the description of each circuit below.
- Letter A- MAF Signal.
- Letter B- Ground.
- Letter C- 12 Volts
The safest way to test these circuits, and the method I always use, is using a wire piercing probe. (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 the mass air flow sensor from the vehicle or from its plumbing (all of the figures show the MAF sensor off of the vehicle just for illustration purposes only).