TEST 3: Checking The MAF Sensor Signal
OK, now comes the part you signed up for! Let's see if the MAF sensor is producing a MAF Signal.
For this test, you'll need a multimeter that can read Hertz frequency... otherwise you won't be able to test the mass air flow (MAF) sensor.
If you don't have one, and need to buy one that's inexpensive, take a look at this Hertz enabled Multimeter I recommend here: Buying A Digital Multimeter For Automotive Diagnostic Testing (found at: easyautodiagnostics.com).
OK, getting back to the test at hand: The wire that delivers this Hertz Frequency MAF Signal (to the PCM) is the one labeled with the letter A in the photo above.
IMPORTANT: The MAF sensor must remain connected to its electrical connector for this test to work. You'll need to use a back-probe or a wire-piercing-probe to access the signal inside the wire. You can see an example of a wire piercing tool here: Wire Piercing Probe.
This what you'll need to do:
- Place the multimeter in Hertz frequency mode.
- Locate the wire identified with the letter A.
- This is the Yellow wire of the MAF sensor connector.
- Connect the red multimeter test lead to this Yellow wire using an appropriate tool.
- Ground the black multimeter test lead directly on the battery negative (-) terminal.
- Crank and start the engine.
- If the engine is cold, let it warm up a bit so that the idle will settle down a bit.
- Your multimeter should register:
- Around 2.2 to 2.7 K Hertz at idle.
- As you accelerate the engine, the Hertz values should increase.
- At around 1500 RPM you should see about 3.6 to 3.7 K Hertz.
- At around 2000 RPM you should see about 3.9 K Hertz.
- When you release the accelerator, and the engine returns to idle, the Hertz value should return to somewhere close to 2 K Hertz.
Let's take a look at your test results:
CASE 1: The multimeter registered the indicated Hertz values when you accelerated and decelerated the engine: -This tells you that the MAF sensor is OK.
There's no need to replace the MAF sensor, since this test confirms that it's functioning.
CASE 2: The multimeter DID NOT register the indicated Hertz values when you accelerated and decelerated the engine. Make sure that you're testing the correct wire, that your connections are OK, and repeat the test.
If you still don't see the Hertz values going up when you accelerate the engine or go down when you decelerate the engine, then you've got a bad mass air flow (MAF) sensor on your hands.
Replace the MAF sensor.
MAF Test Summary
The most important thing to remember, when testing the MAF sensor is that when it fails... it usually fails in one of two ways:
- It'll stop producing a Hertz signal, even tho' it's getting power and Ground.
- Or, it'll produce a signal that won't go up or down as you accelerate or decelerate the engine.
I'm pointing this out, because you don't need to know a precise Hertz Frequency number for a specific RPM. I know, I know... it would be great to have a specific value to compare against but trust me, you don't need it.
If in TEST 3, the Hertz values went up and down... the MAF on your 3.5L equipped car or pickup is OK.
I know that the focus of this article is pretty narrow... so if you would like to add your two cents to it, for the benefit of anyone else that reads these pages... by all means use the contact form below and share your diagnostic and repair experience.
If this info saved the day, buy me a beer!