How To Test The GM MAF Sensor Express And Savana Van (2003-2008)

The mass air flow (MAF) sensor on your 2003-2008 GMC Savana van or Chevy Express van can be easily tested in three steps and without a scan tool.

In this tutorial, I'll show you how to test it with a digital multimeter that can read Hertz frequency.

You can find this tutorial in Spanish here: Cómo Probar El Sensor MAF De Express y Savana Van (2003-2008) (at: autotecnico-online.com).

APPLIES TO: This tutorial applies to the following vehicle:

• Chevrolet Express Van (1500, 2500, 3500) 4.8L, 5.3L, 6.0L: 2003, 2004, 2005, 2006, 2007, 2008
• GMC Savana Van (1500, 2500, 3500) 4.8L, 5.3L, 6.0L: 2003, 2004, 2005, 2006, 2007, 2008

There are 3 other GM MAF sensor test articles that may come in handy:

• How To Test The GM Mass Air Flow Sensor (Early Type): Buick, Chevy, Olds, Pontiac 3.1L, 3.4L, 4.3L, 5.0L, 5.7L V6 Engines (1996-2005)
• How To Test The GM MAF Sensor: Buick, Chevy, Olds, Pontiac 3.8L V6 Engines (1996-2005)
• 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)

Symptoms Of A Bad GM MAF Sensor

The most obvious one is that the CHECK ENGINE light (CEL) will be on on your instrument cluster and driving you nuts. Here are a couple of others:

1. A MAF sensor diagnostic trouble code (DTC) stored in your vehicle computer's memory.
   • P0101, P0102
2. Lean and/or Rich diagnostic trouble code(s).
   • P0171, P0174
3. Fuel Trim diagnostic trouble code(s).
4. No power when you accelerate the car or truck.
5. Black smoke coming from the tail-pipe.
6. Your car or truck or SUV may idle rough and stall.

What Tools Do I Need?

You'll need a digital multimeter that can read Hertz (Hz) frequency (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). As mentioned earlier, you don't need an automotive scan tool to test the MAF sensor. Having said that... a scan tool is one of those MUST have tools to be able check and diagnose today's modern cars and trucks, but for the tests in this article you don't need one.

Circuit Descriptions Of The MAF Sensor Connector

The MAF sensor on your Express van (or Savana van) has 5 wires coming out of the connector. Each wire (circuit) has a specific job to do and below, you'll find the description. Each of the 3 Tests, that make up this article, will use these circuit descriptions:

• Circuit labeled 1:
  • Air Temperature Sensor Circuit
• Circuit labeled 2:
  • Air Temperature Sensor Circuit
• Circuit labeled 3:
  • Ground Circuit.
• Circuit labeled 4:
  • Power (12 Volts) Circuit.
• Circuit labeled 5:
  • MAF Signal Circuit.

I did not include the color of the wires because as long as you're able to identify them by the number in the photo, you'll be OK. Also, the color of the wires in the photos may not be the color of the wires of the MAF on your specific vehicle and again this is no cause for concern.

Basic Working Theory Of The GM MAF Sensor

The fuel injection computer needs to know the amount of air the engine is breathing to inject the correct amount of fuel (among several things) and keep your GM van idling or running smooth. For this, the PCM relies on the mass air flow sensor.

The MAF sensor's job is to measure the amount of air the engine is breathing at any given RPM. It then converts this measurement into a Hertz frequency reading (as measured by a digital multimeter that can read Hz frequency) and shoots it to the PCM. Here's what it looks like on a digital multimeter:

• At an idle of about 680 RPMs, the MAF sensor outputs about 3.2 K Hertz.
• At about at 1500 RPM;s the MAF signal output is about 4.2 K Hz.
• At 2500 RPMs it hovers around 5.2 K Hz.

As you can see, the more air the engine breathes (or the higher the RPMs) the higher the MAF output signal becomes, and of course the less air the engine breathes, the lower the reading on your digital multimeter. Now, in testing the MAF sensor, you won't be looking for a specific Hertz (Hz) number at a specific RPM, but for crazy fluctuations in the signal that don't correspond to the amount of air entering the engine or NO SIGNAL AT ALL. OK, crash course is over, let's start testing.

TEST 1: Testing The MAF Signal Circuit

To get our MAF sensor diagnostic under way, we're gonna check the sensor's output signal with a multimeter (with Hertz measurement capability).

If the MAF sensor is good, its output signal should increase as engine RPMs increase. As engine RPMs decrease, the output signal should decrease.

Generally, you'll see something like this:

• At an idle of about 680 RPMs, the MAF sensor outputs about 3.2 K Hertz
• At about at 1500 RPM;s the MAF signal output is about 4.2 K Hz.
• At 2500 RPMs it hovers around 5.2 K Hz.

If the MAF sensor is bad, you'll generally see the Hertz signal value stuck in one value regardless of engine RPM.

To test the MAF sensor output signal, it's important that your Express van or Savana van's engine be at normal operating temperature. So, if it isn't already warmed up, go ahead and start 'er up and let run for a few minutes.

This is what you'll do:

1. 1

   With the key in the OFF position.

2. 2

   Connect the red multimeter test lead to the wire identified with the number 5 (see photo above).

3. 3

   Put the multimeter in Hertz frequency (Hz) mode.
   
   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.

4. 4

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

5. 5

   Start the already warmed up engine.

6. 6

   Note the Hertz reading on your multimeter at idle.
   
   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.

7. 7

   Manually accelerate the engine from the engine compartment as you watch the multimeter's frequency readings.
   
   The Hertz frequency readings should increase.

8. 8

   When you let go off of the throttle and the engine returns to idle, the Hertz reading should come down to the base Hertz reading you observed in step 6 of this test.

9. 9

   Repeat this as often as you need to verify that the Hertz numbers on the multimeter rise and decrease smoothly every single time.

Let's interpret your multimeter test results:

CASE 1: The Hertz (Hz) signal rose smoothly and decreased smoothly as the engine was accelerated and decelerated respectively, then this indicates that the mass air flow (MAF) sensor is working correctly.

CASE 2: The Hertz (Hz) signal DID NOT rise smoothly nor decreased smoothly as the engine was accelerated and decelerated respectively. This indicates that the mass air flow (MAF) sensor is bad.

To make sure it's bad, the next test is to make sure it's getting power. Go to: TEST 2: Testing The Ground Circuit.

Oscilloscope Waveform Of The GM MAF Sensor

If you have access to an oscilloscope, this is what the mass air flow (MAF) sensor waveform looks like at idle.

If the MAF sensor is good then at idle and at any RPM, the waveform will stay perfectly formed. Also, as you accelerate the engine, the wave-length will become shorter while the wave amplitude stays the same.

Now, if the MAF sensor is bad, the waveform will have missing pieces or no waveform will be formed at all.