MAF Sensor Test Basics
OK, you're gonna' start by checking the basics. These are 12 Volts and battery Ground to the mass air flow sensor. After that, we'll test the actual performance of the MAF sensor as the engine is running. Use a digital multimeter for all tests where a multimeter is called for.
The MAF sensor produces an analog voltage signal. This MAF signal's DC voltage is directly related to amount of air the engine is breathing. Therefore, if the engine is breathing in more air at 2,500 RPM that at an idle of 900 RPM the voltage output will be greater at 2,500 RPM than at idle.
Now, when testing this voltage signal, the important thing to know is not an actual Volts number at a specific RPM, but to look for crazy and extreme fluctuations in the voltage signal that do not correspond to the actual air intake (RPM) of the engine or no signal at all. For example: If at Idle the voltage reading starts to spike up and down without you accelerating the engine or if there's no signal at all.
In the TEST 4 section of this article, I'll show how you'll use a base voltage reading at idle from the MAF sensor that will help you to confirm that the MAF sensor is bad or not.
TEST 1: Testing The Power (12 V) Circuit
The very first thing that we'll do is check that the MAF sensor is receiving 12 Volts.
The procedure I recommend for you to use (to accomplish all of the tests below) is to use a test probe that pierces thru' the wire's insulation (click here to see a picture of this tool: Wire Piercing Probe).
Also, do not disconnect the round air filter canister assembly from the air duct that connects it to the intake manifold's throttle body.
These are the test steps:
Put the multimeter in Volts DC mode.
Don't have a digital multimeter? Need to buy one? Click here to see my recommendations: Buying A Digital Multimeter For Automotive Diagnostic Testing.
With the red multimeter test lead and an appropriate tool, probe the MAF sensor connector's wire labeled with the number 4,as shown in the photo.
Connect the black multimeter test lead to the battery (-) negative terminal.
Turn the key to the RUN position but don't crank or start the engine.
You should see 10 to 12 Volts on the multimeter.
Let's take a look at your test results:
CASE 1: The multimeter registered 12 Volts -All is good in the neighborhood. Now that you've confirmed that the MAF sensor is getting power your next test is to make sure the MAF is getting a good chassis Ground.
CASE 2: The multimeter DID NOT register 12 Volts -Double check your multimeter connections and retest.
If your multimeter still does not show 12 Volts, then the mass air flow (MAF) sensor is not the problem. Without this voltage the MAF sensor will not work. Correcting the cause of this missing voltage will get the MAF sensor working again.
TEST 2: Testing The Ground Circuit
In the previous test we checked and confirmed that the mass air flow (MAF) sensor is receiving 12 Volts.
Now we'll check that the MAF sensor is getting a good Ground. This Ground is a chassis Ground.
These are the test steps:
Turn key to the OFF position.
Place the multimeter in Volts DC mode.
With the black multimeter test lead and a wire-piercing-probe, probe the MAF sensor connector's wire identified with the number 3, as shown in the photo.
Connect red lead to the battery (+) positive terminal.
You should see a voltage of 10 to 12 Volts.
Let's see what your test results mean:
CASE 1: The multimeter registered 10 to 12 Volts. All is good in the neighborhood since this test result tells you that you do have power Ground (chassis Ground).
Your next step is to make sure that the MAF RTN circuit is providing Ground. This is a Ground that's provided to the MAF sensor by the PCM. For this test, go to: TEST 3: Testing The 2nd Ground Circuit.
CASE 2: The multimeter DID NOT register 10 to 12 Volts. Double check your multimeter connections and repeat the test.
If your multimeter still does not register the indicated 12 Volts, then the MAF sensor itself is not the problem. Without a clear path to Ground in this circuit, the MAF sensor will not work. Correcting the cause of this missing path to Ground will get the MAF sensor working again.