A lot of people think that the only way to test the mass air flow (MAF) sensor is with a scan tool, but that's not the case. The mass air flow (MAF) sensor on your 1998-2002 2.0L Mazda 626 can be tested with a simple multimeter.
This multimeter test is so accurate that its results will tell you if your mass airflow sensor is bad or not. This tutorial will teach you how to do that test in a step-by-step manner.
Contents of this tutorial:
You can find this tutorial in Spanish here: Cómo Probar El Sensor MAF (1998-2002 2.0L Mazda 626) (at: autotecnico-online.com).
NOTE: If you need to test the 1996-1997 2.0L Mazda 626 (2.0L Mazda MX6) mass air flow sensor, the following tutorial will help: How To Test The MAF Sensor (1996-1997 2.0L Mazda 626).
Symptoms Of A Bad MAF Sensor
To give you a little background info on the role that your mass air flow sensor plays on your 2.0L Mazda's fuel injection system, I can tell you that the mass airflow sensor is used by your Mazda's fuel injection computer to find out the amount of air the engine is breathing (at any given moment during engine operation). This makes the mass air flow sensor a very critical input sensor for the engine's management system. This also means that when it fails, your car's performance suffers.
Here's a list of the symptoms you'll when the MAF sensor goes kaput:
- One of the following diagnostic trouble codes (DTCs) is lighting up the check engine light:
- P0101: MAF Sensor Performance.
- P0102: MAF Sensor (MAF) Low Input.
- P0103: MAF Sensor (MAF) High Input.
- Doesn't pass the smog check.
- Engine idles rough.
- Engine takes forever to start (extended cranking time).
- Engine doesn't start.
- Black smoke coming out of the tail-pipe as engine runs.
MAF Sensor Circuit Descriptions
I am pretty sure that by now you've noticed that the mass airflow sensor on your 2.0L Mazda 626 has four wires coming out of its connector. If you've been wondering what each wire does, this section will help you identify them by their color and specific function.
If you take a close look at your MAF sensor (and if it still has the original MAF sensor it came with from the factory), you'll notice that that are 4 letters embossed on it, near its connector. These letters are A, B, C, and D. These letters identify specific circuits:
- Letter D: MAF Signal. Red with green stripe (RED/GRN) wire.
- Letter C: Ground that the ECM provides. Brown with red stripe (BRN/RED) wire.
- Letter B: Ground. Black with red stripe (BLK/RED) wire.
- Letter A: 12 Volts. Red with black stripe (RED/BLK) wire.
NOTE: To test the mass airflow sensor signal you'll need to use a special tool. This special tool is a wire piercing probe or a back probe. Why? Because to test the mass airflow sensor signal, the sensor must remain connected to its electrical connector (while the test is being performed). You can take a look at what a wire piercing probe looks like here: Wire Piercing Probe Tool Review (Power Probe PWPPPPP01).
TEST 1: Checking The MAF Sensor Signal
To be able to successfully diagnose the mass airflow sensor as good or bad, you need to verify that it's creating a voltage signal that corresponds to the amount of air the engine is breathing. This verification is done with a multimeter in Volts DC mode.
To be a bit more specific, the voltage signal that the MAF sensor produces increases as the engine breathes more air in. In other words: as the engine revs up and it's breathing more air, the mass airflow sensor creates a bigger voltage output signal. As engine RPM go down and it breathes in less air, the MAF sensor voltage signal decreases.
You and I can check to see if the mass air flow sensor is actually producing this voltage signal by tapping into the red with green stripe (RED/GRN) wire with a multimeter. In case you're wondering, a bad mass airflow sensor will not create a voltage signal that increases with higher engine RPM. In other words, when you rev up the engine (and the engine breathes in more air) this voltage signal will stay stuck at a certain value.
NOTE: Be careful and take all necessary safety precautions! The MAF test in this section is done with the engine running in your 2.0L Mazda 626.
NOTE: The MAF sensor is tested with it connected to its electrical connector, so don't remove it or unplug it (from its electrical connector). The illustration above shows the MAF sensor unplugged and removed just to make it easier to explain the test.
Alright, these are the test steps:
Set the multimeter to Volts DC mode and probe the RED/GRN wire of the MAF sensor connector with the red multimeter test lead.
The red with green stripe (RED/GRN) wire is the one that connects to MAF sensor pin D in the illustration above.
NOTE: Since the MAF sensor has to remain connected to its electrical connector, you'll need to use a tool like a wire piercing probe to access the signal inside the wire. To see what a wire piercing probe looks like, go here: Wire Piercing Probe.
Ground the black multimeter test lead directly on the battery negative terminal.
Have a helper start the engine. Wait for the engine's idle to stabilize and observe your multimeter's voltage reading.
With the engine idling, the voltage reading should be about 1.5 to 1.8 Volts DC.
Now, have your helper accelerate the engine. The voltage should increase.
At around 4,000 RPMs, the multimeter should register to about 3 Volts DC.
Decelerate and accelerate the engine several times as you observe the multimeter
Your multimeter should register a decrease/increase in voltage as you decelerate/accelerate the engine if the MAF sensor is good.
If the MAF sensor is bad, the voltage will be stuck at a certain number no matter how much you accelerate/decelerate the engine.
OK, let's take a look at what your MAF sensor test results mean:
CASE 1: The MAF sensor produced and increasing/decreasing voltage signal as you accelerated/decelerated the engine: This tells you that the mass air flow sensor is OK (not defective).
CASE 2: Your multimeter registered voltage, but it did not increase or decrease as you accelerated/decelerated the engine: This usually confirms that the mass air flow (MAF) sensor on your 2.0L Mazda 626 is bad. Replacing the MAF sensor will solve the MAF sensor trouble code lighting up the check engine light.
Before you conclude the MAF sensor is bad, make sure it's getting power (10-12 Volts) and that it's getting both chassis Ground and sensor ground. Start with the next test: TEST 2: Verifying The MAF Sensor Is Getting Power.
CASE 3: Your multimeter registered 0 Volts. This usually means that the MAF sensor is fried. To be absolutely sure, I suggest confirming that the MAF sensor has power and its two grounds. If both (power and its two grounds) are present, the MAF sensor is bad.
To test for power, go to: TEST 2: Verifying The MAF Sensor Is Getting Power.