How To Test The MAF Sensor (1997, 1998 3.0L Mitsubishi Montero)

TEST 4: Testing The MAF Reset Signal

The MAF Reset Signal is just an On/Off type DC voltage signal that turns 'ON' when the throttle plate opens and turns 'OFF' when the throttle plate closes.

This is a pretty simple test that we can accomplish with the multimeter in Volts DC mode.

NOTE: This test is performed with the MAF sensor connected to its harness connector. To access the signal inside the 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 this tool here: Wire Piercing Probe.

Here are the test steps:

1. 1

   Place the multimeter in Volts DC mode.

2. 2

   Connect the red multimeter test lead to the wire that connects to the connector terminal identified with the number 7 (see the illustration above) using an appropriate tool.

3. 3

   Connect the black multimeter test lead to the battery negative (-) terminal.

4. 4

   Crank and start the engine.

5. 5

   Manually open and close the throttle plate from the engine compartment as you observe the multimeter.
   
   NOTE: Since the engine will be running, take all necessary safety precautions.

6. 6

   With the engine at idle and the throttle plate closed, your multimeter should register around 1 Volt DC or less. This is the 'Off' voltage reading.

7. 7

   Open the throttle plate about 1/3 or more. Your multimeter should register 6 to 9 Volts. This is the 'On' voltage reading.

8. 8

   Let go of the throttle plate and let it close (causing the engine to return to idle). The multimeter should register the voltage you observed in step 6 of this test.

Let's take a look at what your test results mean:

CASE 1: The multimeter registered the 'On' and 'Off' voltage readings. This is the correct test result and it indicates that the mass air flow sensor is creating the MAF Reset Signal. Your MAF sensor is working properly.

CASE 2: The multimeter DID NOT register the 'On' and 'Off' voltage readings. Recheck all of your multimeter connections and retest. If the indicated voltages are still not present then your 3.0L Mitsubishi Montero's MAF sensor is not functioning correctly. Replace the MAF sensor.

Mitsubishi MAF Sensor Signal Wave Form

If you have access to an oscilloscope, this is what the mass air flow (MAF) sensor waveform looks like at idle.

If the MAF sensor is good then at idle and at any RPM, the waveform will stay perfectly formed. Also, as you accelerate the engine, the wave-length will become shorter while the wave amplitude stays the same.

Now, if the MAF sensor is bad, the waveform will have missing pieces or no waveform will be formed at all.

More 3.0L Mitsubishi Tutorials

You can find a complete list of 3.0L Mitsubishi tutorials here: Mitsubishi 3.0L Index Of Articles.

Here's a small sample of the tutorials you'll find in the index:

• How To Test Engine Compression (3.0L Mitsubishi).
• How To Test The Throttle Position Sensor (3.0L Mitsubishi Montero).
• Testing The Power Transistor, Ignition Coil, and Crank Sensor.
• How To Bench Test A Starter Motor (Step By Step).