MAF TEST 3: Testing The 2nd Ground Circuit

Making Sure The MAF Sensor Is Getting PCM Ground. How To Test The Ford Mass Air Flow (MAF) Sensor

Now, we'll check the second Ground circuit of the MAF sensor. This Ground is provided by the fuel injection computer internally.

CAUTION: When testing this circuit, you've got to be careful and take extreme care not to short-circuit this wire to battery 12 Volts or you'll fry the fuel injection computer. The multimeter test I'm suggesting below is a safe way to test for the presence of Ground in the wire.

OK, this is are the steps:

  1. 1

    Disconnect the MAF sensor from its electrical connector.

  2. 2

    Place your multimeter in Volts DC mode.

  3. 3

    With the black multimeter test lead and an appropriate tool, probe the wire identified with the letter letter C in the photo.

  4. 4

    Connect the red multimeter test lead probe the battery positive (+) terminal.

  5. 5

    You should see 12 Volts on the multimeter.

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

CASE 1: Your multimeter registered 12 Volts. This is the correct result, the next step is to make sure the MAF sensor has Ground, for this, go to: MAF TEST 4: Testing The MAF Signal.

CASE 2: Your multimeter DID NOT register 12 Volts. Recheck all of your multimeter connections and retest. If you still do not see these 12 Volts, then this exonerates the MAF sensor as bad since without this Ground it's not gonna' work.

MAF TEST 4: Testing The MAF Signal

Testing The MAF Signal. How To Test The Ford Mass Air Flow (MAF) Sensor

Now that you've gotten the power and Ground signals out of the way, you'll test the MAF sensor's signal.

It's important that the engine be at its normal operating temperature. So, start the engine and let it reach it's normal operating temperature.

I know I'm stating the obvious, but the MAF sensor must be connected to its connector to perform this test. OK, let's start:

  1. 1

    Place your multimeter in Volts DC mode.

  2. 2

    Reconnect the MAF sensor to its electrical connector.

  3. 3

    With a suitable tool connected to the red multimeter test lead, probe the wire labeled with the letter D in the photo above.

  4. 4

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

  5. 5

    Crank and start the engine and let her idle.

    Once the idle stabilizes, take a look at the voltage number or numbers your multimeter is throwing at you. This voltage may fluctuate a little or a lot, and this is OK. Whatever they're doing, this is your base MAF signal voltage.

  6. 6

    Now, open the throttle (manually) to rev up the engine.

    As the engine revs up, keep your eyes on the multimeter's voltage numbers.

    The voltage value should increase as the engine RPM increases.

  7. 7

    Let go off of the throttle and let the idle come down.

    The voltage reading should decrease and should hover around the numbers you noticed at the beginning of this test.

  8. 8

    Rev up/rev down the engine several times. Each time, the voltage numbers on your multimeter should increase/decrease smoothly.

  9. 9

    If the MAF sensor is good, the voltage numbers on the multimeter should rise and fall smoothly and without gaps.

    If the MAF sensor is bad, the voltage will stay stuck in one value as your rev up/rev down the engine.

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

CASE 1: The voltage value increased/decreased as you accelerated/decelerated the engine. This tells you that the MAF sensor is good and not the cause of the MAF issue or diagnostic trouble code.

CASE 2: The voltage value stayed stuck in value as you accelerated/decelerated the engine. Recheck all of your multimeter connections and retest.

If you still do not see the indicated voltage rising and falling smoothly, then the mass air flow (MAF) sensor is bad. Replace the MAF sensor.

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Mazda Vehicles:

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