TEST 1: Checking The MAF Sensor Signal
The most common type of mass airflow sensor failure is a sensor that stops measuring the amount of air entering the engine. This results in an output voltage that stays stuck at a specific voltage value irregardless of engine RPM. Remember this output voltage value should increase with higher engine RPM and decrease as these engine RPM return to idle RPM.
So in this first test we're going to check to see if the mass air flow sensor output voltage is stuck at a specific value or if it is increasing/decreasing as we rev the engine up and down.
The wire that delivers this MAF voltage signal (to the PCM) is the one labeled with the number 2 in the photo above.
NOTE: This test must be done with the mass air flow sensor connected to its electrical connector. So you'll need to use a back probe or a wire piercing probe to test output voltage signal of the wire. You can see what a wire piercing probe looks like here: Wire Piercing Probe.
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 2. 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.
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 or less.
Let's take a look at what your test results mean:
CASE 1: The MAF signal value increased/decreased as you revved the engine up and down: 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 MAF signal stayed stuck in one value when you revved the engine up and down: This test result usually tells you that you've got a bad mass air flow (MAF) sensor on your hands.
To make sure that the MAF sensor is bad, you need to confirm that it's getting both power and Ground. This is another simple multimeter test. Go to: TEST 2: Making Sure The MAF Sensor Is Getting Power And Ground.
TEST 2: Making Sure The MAF Sensor Is Getting Power And Ground
The MAF sensor gets power (in the form of 12 Volts DC) from the wire labeled with the number 3 in the photo above. Ground is supplied by the wire labeled with the number 1.
To test both, we'll do a simple multimeter voltage test.
These are the test steps:
Remove enough of the plastic tubing that is sheathing the MAF sensor's three wires. The idea is to expose enough of the three wires to be able to test them.
Disconnect MAF sensor from its connector and place your multimeter in Volts DC mode.
Verify that the wire labeled with the #3 (in the photo above) has 10 to 12 Volts with the key on but engine off.
A.) Connect the red multimeter test lead (using the appropriate tool) to the wire that connects to terminal #3.
B.) Connect the black multimeter test lead to the negative (-) battery terminal.
c.) Your multimeter should read 10 to 12 Volts DC.
Verify that the wire labeled with the #1 (in the photo above) has Ground with the key on but engine off.
A.) Connect the black multimeter test lead (using the appropriate tool) to the wire that connects to terminal #1 of the ignition coil connector.
B.) Connect the red multimeter test lead to the positive (+) battery terminal.
C.) Your multimeter should read 10 to 12 Volts DC.
Let's take a look at what your test results mean:
CASE 1: The multimeter confirms power and Ground are present. This is the correct and expected test result.
If the MAF sensor failed TEST 1 (did not register and increasing/decreasing voltage output signal as you revved the engine up and down) then by having confirmed that it's getting power and Ground, you can conclude correctly that the mass airflow sensor is bad. Replacing the MAF sensor should solve the problem.
CASE 2: The multimeter shows power is missing (on wire #3) This test result tells you that power is behind the MAF sensor's malfunction. Without these 10 to 12 Volts, your Mazda's MAF sensor won't work.
Although it's beyond the scope of this tutorial, your next step is to find out why these 12 Volts are missing. Resolving these missing 12 Volts will get the MAF sensor working again.
CASE 3: The multimeter shows Ground is missing (on wire #1) This test result tells you that a Ground problem is causing the MAF sensor malfunction. Without a path to Ground, your Mazda's MAF sensor won't work.
Although it's beyond the scope of this tutorial, your next step is to check and resolve this missing ground.
If this info saved the day, buy me a beer!