TEST 3: Checking The MAF Sensor Signal
If you've reached this point, then you've confirmed that your Mazda's MAF sensor is being fed with both power and Ground.
The next step is to test your MAF sensor in action and see if it's producing a viable MAF sensor signal.
The wire that delivers this MAF voltage signal (to the PCM) is the one labeled with the number 3 in the photo above.
This what you'll need to do:
Place the multimeter in Volts DC mode. The signal that the MAF sensor produces is an analog DC voltage signal.
Locate the wire identified with the number 3. This is the green with black stripe (GRN/BLK) wire of the MAF sensor connector.
Connect the red multimeter test lead to the green with black stripe wire using an appropriate tool (like a Wire Piercing Probe).
Connect the black multimeter test lead directly to 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.
At idle, your multimeter should register a MAF voltage of around 1.1 Volts DC.
Now accelerate the engine, the voltage values should increase.
At around 2000 RPM your multimeter should register about 1 0.5 Volts DC. At around 3000 RPM your multimeter should register about 1 0.7 Volts DC.
NOTE: Remember these voltage numbers only serve as a guideline. The actual numbers you MAF sensor outputs may be a little different. What you're looking for is for the voltage to increase as you rev up the engine.
When you release the accelerator, and the engine returns to idle, the voltage value should return to somewhere close to 1.1 Volts DC.
Let's take a look at what your test results mean:
CASE 1: The multimeter registered the indicated voltage values when you accelerated and decelerated the engine. This is the correct and expected test result and tells you that the mass air flow (MAF) sensor is good.
If the mass air flow (MAF) sensor were bad, the voltage would have not gone up or down as you revved the engine up and down.
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 voltage 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 voltage 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.
If this info saved the day, buy me a beer!