How To Test The GM MAF Sensor (3.1L, 3.4L, 4.3L, 5.0L And 5.7L)

This is one of the easiest mass air flow sensors to test! In this tutorial, you'll find an on-car test that checks the performance of the MAF sensor with the engine running.

This GM MAF sensor test is performed with a multimeter that can read Hertz (Hz) frequency. No scan tool is required or any other expensive testing equipment!

You can find this tutorial in Spanish here: Cómo Probar El Sensor MAF GM 3.1L, 3.4L, 4.3L, 5.0L, y 5.7L (at: autotecnico-online.com).

In the box titled Applies To:, you'll find a complete list of GM makes and models (and Isuzu) that use this type of MAF sensor. Now, in case this is not the article you're looking for, there are also 3 other GM MAF sensor test articles:

• How To Test The GM Mass Air Flow Sensor: GMC Savana Van and Chevy Express Van 4.3L, 5.3L, 6.0L Engines (2003-2008)
• How To Test The GM Mass Air Flow (MAF) Sensor: 4.8L, 5.3L, 6.0L, and 8.1L V8 Engines (1999-2010)
• How To Test The MAF Sensor on 3.1L, 3.3L, and 3.8L Buick, Oldsmobile, Pontiac (1988-1996)
• How To Test The GM MAF Sensor: Buick, Chevy, Olds, Pontiac 3.8L V6 Engines (1996-2005)

Is The MAF Sensor Just Dirty (Contaminated)?

The most important thing to do before starting with the mass air flow sensor test, is to make sure your MAF sensor's wires aren't contaminated with dirt (since the tests in this article assume the MAF sensor isn't contaminated).

Why? Because this MAF sensor is a hot wire sensor type that easily becomes contaminated with dirt and stuff if the air filter isn't performing its job.

This contamination will appear as a type of ‘fuzz’ on the two wires of the sensor. You can see an example of a dirty MAF sensor here: Dirty MAF Sensor Example (Fly Stuck in MAF Sensor).

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 response that is felt after the accelerator pedal is depressed. Other symptoms may include but are not limited to: higher tailpipe emissions and diagnostic codes that may illuminate the "Check Engine" light.

If the sensor wires are dirty, use an electronics spray cleaner to clean them with. This in itself may solve your problem. I don't recommend using carb or brake clean spray. These solvents can damage the sensor.

Also, don't attempt to physically clean the sensor with anything. You'll find all auto-part stores sell the correct cleaning spray. If you'd like to see the MAF sensor cleaning process explained step by step click here: How To Clean The Mass Air Flow Sensor.

Common Symptoms Of A Bad MAF Sensor

This list is not all inclusive but it does contain the most common symptoms of a bad MAF sensor are:

1. The check engine light (CEL) on your instrument cluster is lit nice and bright with one of the following codes:
   • P0101   Mass Air Flow System Performance.
   • P0102   Mass Air Flow Low Frequency.
   • P0103   Mass Air Flow High Frequency.
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.

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).

TEST 1: Testing The MAF Signal

For our first test, we'll check the MAF signal coming out of the sensor and going to the ECM.

As I mentioned earlier, you'll need a multimeter that can read Hertz Frequency values since the MAF digital signal voltage output oscillates pretty darn fast.

Before you start the test, it's a good idea to start the engine and let it reach its normal operating temperature.

Once the engine has reached its normal operating temperature and the engine's idle has stabilized, you'll take a Hertz reading of the MAF signal which you'll need as a base reading to diagnose the MAF sensor.

NOTE: The MAF sensor must be connected to its connector to perform this test. You'll need to use a back probe on the connector or a wire-piercing probe on the wire. You can see an example of this tool and where to buy it here: Wire Piercing Probe.

These are the test steps:

1. 1

   Place your multimeter in Hertz (Hz) mode.
   
   If you need to buy a Hertz enabled multimeter or need to upgrade to one, check out my recommendations here: Buying A Hertz Digital Multimeter for Automotive Diagnostic Testing.

2. 2

   Connect the red multimeter test lead to the wire labeled with the letter A in the photo above.
   
   NOTE: The MAF sensor must remain connected to its connector to perform the MAF signal verification test.

3. 3

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

4. 4

   Start the already warmed up engine.
   
   Once the idle stabilizes, observe the Hertz reading on your multimeter is registering.
   
   This reading may be stable (with only small fluctuations) or unstable with very extreme fluctuations. No matter what the instability in the reading, this will be your base reading.

5. 5

   Manually accelerate the engine from the engine compartment.

6. 6

   The Hertz Frequency readings should increase as the engine RPMs increase.

7. 7

   Let go off of the throttle and the engine returns to idle.

8. 8

   The Hertz reading should come down to the base Hertz reading you observed in step 3 of this test.

9. 9

   Repeat accelerating/decelerating the engine.

10. 10

    The Hertz numbers should increase/decrease as you accelerate/decelerate the engine.

Let's interpret your test result:

CASE 1: The Hertz numbers rose and fell as you accelerated and decelerated the engine. This tells you that the MAF sensor is good and not the cause of the MAF issue or diagnostic trouble code.

To be a bit more specific: If the Hertz reading increased as you revved up the engine and then decreased as the engine returned to its idle RPMs, then the MAF sensor is working like it should.

CASE 2: The value registered on the multimeter stayed stuck in one value Recheck all of your multimeter connections and retest.

If you still don't see the indicated Hertz values, the next step is to make sure the MAF sensor is getting power. Go to: TEST 2: Testing The Power Circuit.

MAF Sensor Signal Waveform

If you're using an oscilloscope, the MAF sensor's signal waveform should look like the one above.