Mass Air Flow (MAF) Sensor Test Nissan Sentra 1.6L (1995-1999)

TEST 2: Testing The Ground Circuit

In the previous test we checked that the sensor was receiving 12 Volts. Now we'll check that the MAF sensor is getting a good Ground. This Ground is provided by the ECM internally.

The wire that supplies Ground to the MAF sensor is the one labeled with the number 2 in the photo above.

Be careful and take extreme care not to short-circuit this wire to Ground or power as you're probing it.

Let's get started:

1. 1

   Place your multimeter in Volts DC mode.

2. 2

   Disconnect the MAF sensor connector from the MAF sensor.

3. 3

   Probe the MAF sensor wire labeled with the number 2 with the black multimeter test lead (and the appropriate tool).

4. 4

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

5. 5

   Turn the key on but don't crank or start the engine.

6. 6

   You should see 12 Volts on the multimeter if the MAF sensor is being fed power.

Let's interpret your Ground test result:

CASE 1: The multimeter registered 12 Volts -This is the correct and expected test result.

Now for the last test, which is testing the MAF signal itself. Go to: TEST 3: Testing The MAF Signal With A Multimeter.

CASE 2: The multimeter DID NOT register 12 Volts -The MAF sensor is not the problem. Without this Ground the MAF sensor will not work.

Although it's beyond the scope of this tutorial, your next step is find out why this Ground is missing and restore it.

TEST 3: Testing The MAF Signal With A Multimeter

Now that the basics have been checked, we'll check the MAF signal coming out of the sensor and going to the ECM.

Start the engine and let it reach it's normal operating temperature. You'll be using the voltage reading you will obtain at idle as a base to diagnose the MAF sensor.

As mentioned at the beginning of this tutorial, the MAF signal reacts to amount of air the engine is breathing. So if you accelerate the engine, the MAF sensor signal voltage will increase.

If the MAF sensor is bad on your Nissan Sentra, the voltage reading will stay stuck in one value no matter how much you accelerate the engine.

IMPORTANT: The MAF sensor must be connected to its connector to perform this test. So you'll need to use a back-probe or a wire piercing probe to access the signal inside the wire. To see an example of a wire piercing probe, check this link out: Wire Piercing Probe.

These are the test steps:

1. 1

   Connect the red multimeter test lead to the wire labeled with the number 1 shown in the photo.

2. 2

   Put your multimeter in Volts DC mode.

3. 3

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

4. 4

   Start the already warmed up engine.

5. 5

   Note the Volts reading on your multimeter at idle. This reading may be stable (with only small fluctuations) or unstable with very extreme fluctuations. No matter what the instability in the reading, this will be your base reading.

6. 6

   Accelerate the engine as you watch the multimeter's voltage readings.
   
   The MAF signal voltage value should increase as you rev up the engine.

7. 7

   Let the engine return to idle.
   
   The MAF signal voltage value should decrease as the engine returns to idle.

8. 8

   The voltage value should rise/fall every time you rev up/down the engine.
   
   If the MAF sensor is defective, the MAF signal voltage value will stay stuck in one single number as you rev up/down the engine.

Let's interpret your MAF signal test result:

CASE 1: The MAF signal rose smoothly and fell smoothly according to the engine's RPMs. This test result tells you the MAF is OK. In other words, the MAF sensor is creating a MAF signal and IS NOT defective.

CASE 2: The MAF signal DID NOT rise smoothly or fall smoothly according to the engine's RPMs or if there was no MAF signal at all. This test result indicates the MAF sensor is bad.

Here's the reason why:

1. You have confirmed that the MAF sensor is getting power (TEST 1).
2. You have confirmed that the MAF sensor is getting Ground (TEST 2).
3. In this test step, you have confirmed that the MAF sensor is NOT creating a voltage signal that increases with higher engine RPMs and decreases when the engine returns to idle.

Taking the above into account, you can conclude that the MAF sensor is bad and needs to be replaced.