TEST 3: Checking The MAF Sensor Signal With A Multimeter
If you've reached this point, you've confirmed that:
- The mass air flow sensor is getting 12 Volts.
- The mass air flow sensor is getting Ground.
For our third and last test, we're going to check the mass air flow sensor's voltage signal.
Specifically, we want to make sure that the voltage signal increases as you accelerate the engine and that it decreases as you decelerate the engine.
If a mass air flow sensor is bad, the voltage signal with a stuck at one value as you accelerate/decelerate the engine.
IMPORTANT: The mass air flow sensor must remain connected to its electrical connector for this test to work. To access the voltage inside the signal wire, you'll need to use a back-probe on the connector or a wire piercing probe on the wire. You can see an example of the tool here: Wire Piercing Probe.
These are the test steps:
Place the multimeter in Volts DC mode.
Connect the red multimeter test lead to the light green with black stripe wire using an appropriate tool.
In the photo above, the LT GRN/BLK wire is labeled with the number 2.
Connect 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.
At idle, your multimeter should register a MAF voltage between 1 to 2 Volts DC.
Now accelerate the engine, the voltage value should increase.
Release the accelerator, the voltage value should decrease and return to somewhere between 1 to 2 Volts DC.
Let's take a look at what your test results mean:
CASE 1: The MAF signal voltage increased/decreased as you accelerated/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 stayed stuck in one value as you revved the engine up and down.
CASE 2: The MAF signal voltage stayed stuck in one value as you accelerated/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.
More 1.5L Mazda Protege Tutorials
You can find a complete list of 1.5L Mazda Protege tutorials in this index:
Here's a small sample of the tutorials you'll find in the index:
- P0122 -What Does It Mean? (1996-1998 1.5L Mazda Protege).
- P0123 -What Does It Mean? (1996-1998 1.5L Mazda Protege).
- How To Test The TPS (1996-1998 1.5L Mazda Protege).
If this info saved the day, buy me a beer!