Testing to see if the MAF sensor on your 3.5L GM equipped car or pickup or SUV is BAD or not can easily be done with a multimeter.
In this article I'll show you how to do it in a step-by-step fashion... that will either condemn the mass air flow (MAF) sensor as BAD or exonerate it.
This MAF sensor is not cheap... so being able to say that it's truly BAD or not will save you some money.
To help you navigate this article, here are its main points:
- Symptoms Of A BAD MAF Sensor.
- What Tools Do I Need To Test The MAF Sensor?
- What Does The MAF Sensor Do?
- TEST 1: Checking The MAF Sensor Power Circuit.
- TEST 2: Checking The MAF Sensor Ground Circuit.
- TEST 3: Checking The MAF Sensor Signal.
You can find this tutorial in Spanish here: Cómo Probar El Sensor MAF (GM 3.5L) (at: autotecnico-online.com).
Symptoms Of A BAD MAF Sensor
When the MAF sensor goes BAD, you'll get the Check Engine Light to shine nice and bright on your instrument cluster.
You'll also see one or several of the following symptoms of a BAD MAF sensor:
- Diagnostic Trouble Codes:
- P0101: Mass Air Flow (MAF) Sensor System Performance
- P0102: Mass Air Flow (MAF) Sensor Circuit Low Frequency.
- P0103: Mass Air Flow (MAF) Sensor Circuit High Frequency.
- BAD gas mileage.
- Rough idle.
- Lack of power on acceleration.
- Black smoke coming out of the tailpipe.
- Won't pass the emissions test.
It's rare for the Mass Air Flow (MAF) Sensor to go BAD and not leave a diagnostic trouble code... but sometimes you'll get the MAF Trouble Code and the MAF is good. So, it's always a good idea to test it.
What Tools Do I Need To Test The MAF Sensor?
Here's a basic list of tools you'll need:
- Multimeter that can read Hertz frequency.
- If you need to upgrade or buy a multimeter that can read Hertz frequency, check out my recommendation: Buying A Digital Multimeter For Automotive Diagnostic Testing (found at: easyautodiagnostics.com).
- Wire Piercing Probe.
- Although this tool is not an absolute must, if you do buy one, you'll realize just how easy it makes testing the voltages inside the wires.
- If you need to see what this tool looks like, you can see it here: Wire Piercing Probe.
A scan tool comes in handy... but you won't need it to use the testing info in this article.
What Does The MAF Sensor Do?
The MAF sensor is tasked with measuring the amount of air entering the engine at any given RPM. The PCM (Powertrain Control Module = Fuel Injection Computer) then uses this measurement of air flow to inject the correct amount of fuel.
To get into more specifics: The MAF sensor informs the amount of air flow by converting the measurement of air into a Hertz Frequency signal that increases with more air flow (as you accelerate the engine) or decreases as the engine breathes less air.
This Hertz Frequency signal is sent directly to the PCM. Here's what it looks like on a digital multimeter (that can read Hertz):
- At an idle of about 680 RPM, the MAF sensor outputs about 2.2 K Hertz.
- At about at 1500 RPM the MAF Signal output is about 3.6 K Hz.
- At 2500 RPM it hovers around 4.2 K Hz.
The important thing to know, is that the more air the engine breathes (or the higher the RPM) the higher the MAF Hertz signal becomes, and of course the less air the engine breathes, the lower the Hertz signal (that your digital multimeter will record).
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.
These are the circuit descriptions of the Mass Air Flow (MAF) Sensor
|MAF Sensor Connector Pin Out|
|A||Yellow||MAF Sensor Signal Output|
|B||Black w/ White stripe||Chassis Ground|
|C||Pink||12 V. Ignition Fused Feed|
|D||Tan||Intake Air Temp (IAT) Sensor|
|E||Black||Intake Air Temp (IAT) Sensor|