How To Test The MAF Sensor (1998-2002 2.0L Mazda 626)

TEST 4: Verifying The MAF Sensor Is Getting Ground 2

Now that you've confirmed that the MAF sensor is not creating an increasing voltage signal (when you rev up the engine), that it's getting power (12 Volts), and that chassis Ground is present, we're going to make sure that the MAF sensor is getting a second Ground.

The Ground we're about to verify, in this test section, is provided by your Mazda 626's fuel injection computer. This Ground is called a Signal Return and is a Ground that's part of the air flow sensing part of the sensor.

This Ground is provided to the MAF sensor by the brown with red stripe (BRN/RED) wire of the MAF sensor electrical connector.

Testing for Ground is done with another simple multimeter voltage test.

CAUTION: Since this Ground is provided internally by your Mazda's fuel injection computer, you need to be careful you don't short this wire to 12 Volts (battery power). Shorting this wire to battery power will fry your Mazda's fuel injection computer. The multimeter voltage test described in this section is the safest way to test this circuit.

These are the steps:

1. 1

   Set your multimeter to Volts DC mode and turn the ignition key to its ON position (but don't crank or start the engine).

2. 2

   Probe the BRN/RED wire with the black multimeter test lead.
   
   The brown with red stripe (BRN/RED) wire is the one that connects to the MAF sensor connector's terminal C in the illustration above.
   
   CAUTION: Do not probe the front of the connector or you risk damaging the female metal terminal of the connector.

3. 3

   Now connect the red multimeter test lead on the battery's positive (+) post.

4. 4

   If the BRN/RED wire has Ground, then your multimeter will register 10 to 12 Volts DC.

OK, let's take a look at what your results mean:

CASE 1: The multimeter confirms that the BRN/RED wire is feeding Ground to the MAF sensor. This is the correct test result and confirms that the MAF sensor is bad and needs to be replaced.

You can conclude that the MAF sensor is bad (and that it needs to be replaced) only if you have verified:

• That the MAF sensor is not producing the correct signal voltage values when you accelerate/decelerate the engine (TEST 1).
• That it is being fed with power on the RED/BLK wire (TEST 2).
• That the MAF sensor does have a solid path to chassis Ground on the BLK/RED wire (TEST 3).
• That the MAF sensor does have a solid path to computer Ground on the BRN/RED wire (TEST 4).

These test results, interpreted together, indicate that the MAF sensor is bad.

CASE 2: The multimeter confirms that the BRN/RED wire IS NOT feeding Ground to the MAF sensor: double check your multimeter connections and repeat the test. If your multimeter results still do not indicate 12 Volts, then the mass air flow (MAF) sensor is not fried and not the cause of the MAF sensor diagnostic trouble code (DTC) issue.

Here's why: Without a good path to Ground, that the PCM provides internally, the MAF sensor will not work. With this test result, you have eliminated the MAF sensor as bad.