How To Test The 2000-2002 Nissan Sentra 1.8L MAF Sensor

TEST 2: Verifying The MAF Sensor Is Getting Ground

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 fuel injection computer internally.

Be careful and take extreme care not to short-circuit this wire to Ground or power as you're probing it (or you'll fry the computer).

This wire (circuit) can also be tested with the connector connected to mass air flow (MAF) sensor or not.

This is what you'll need to do:

1. 1

   Probe the wire that's labeled with the number 3 in the photo with the black multimeter test lead.

2. 2

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

3. 3

   Now, turn the Key to the ON position but do not crank or start your Nissan Sentra.

4. 4

   Your multimeter (in Volts DC mode) should register about 11 to 12 Volts DC.

Let's take a look at what your test result means:

CASE 1: The multimeter registered 12 Volts: this result confirms the fuel injection computer is providing a path to Ground. The next step is to check the 5 Volt Reference circuit. Go to: TEST 3: Verifying The 5 Volt Reference Voltage.

CASE 2: Multimeter DID NOT register 12 Volts: Recheck all of your test connections and repeat the test. If still no voltage, then this result exonerates the MAF sensor since without a path to Ground, it's not gonna' work.

Finding the source/cause of the lack of Ground will get your MAF sensor back to functioning.

Altho' it's beyond the scope of this article to test for this missing Ground, the most common cause for this condition is one of two things: An open-circuit problem in the wire between the sensor and the computer, or a bad computer. You have at least eliminated the MAF sensor itself as the cause of the problem.

TEST 3: Verifying The 5 Volt Reference Voltage

The MAF sensor on your 1.8L Nissan Sentra gets a 5 Volt Reference signal from the fuel injection computer and in this test step, we'll make sure it's being received.

Once again, you'll need to be extra careful and take extreme care not to short-circuit this wire as you're probing/testing it (or you'll fry the computer).

This wire (circuit) can also be tested with the connector connected to mass air flow (MAF) sensor or not.

This is what you'll need to do:

1. 1

   Probe the wire that's labeled with the number 2 in the photo with the red multimeter test lead.

2. 2

   Ground the black multimeter test lead by connecting it to the battery negative (-) terminal.

3. 3

   Now, turn the Key to the ON position but do not crank or start your Nissan Sentra.

4. 4

   Your multimeter (in Volts DC mode) should register about 4.5 to 5 Volts DC.

Let's take a look at what your test result means:

CASE 1: The multimeter registered 4.5 to 5 Volts: this result confirms the fuel injection computer is providing a path to Ground. The next step is to check the 5 Volt Reference circuit. Go to: TEST 4: Testing The MAF signal voltage.

CASE 2: Multimeter DID NOT register the indicated Volts: Recheck all of your test connections and repeat the test. If still no voltage, then this result exonerates the MAF sensor since without these 5 Volts, it's not gonna' work.

Finding the source/cause of the missing 5 Volts will get your MAF sensor back to functioning.

Altho' it's beyond the scope of this article to test for these missing 5 Volts, the most common cause for this condition is one of two things: An open-circuit problem in the wire between the sensor and the computer, or a bad computer. You have at least eliminated the MAF sensor itself as the cause of the problem.

TEST 4: Testing The MAF Signal Voltage

OK, this is the final test, and this one will tell you if your MAF sensor is OK or not working.

The engine in your 1.8L Nissan Sentra must be at normal operating temperature. So if it's cold, start the engine and let it warm up.

Also, the MAF sensor must be connected to its connector to perform this test.

This is what you'll need to do:

1. 1

   With the key in the OFF position, probe the wire labeled with the number 1, of the MAF sensor connector shown in the photo.

2. 2

   Start the already warmed up engine and 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.

3. 3

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

4. 4

   Rev up and decelerate the engine several times. Each time, the voltage on the multimeter should go up (in a smooth linear fashion) and come down.
   
   NOTE: You're not looking for specific voltage numbers at specific RPMs. The important thing is to see the voltage increase as you rev up the engine. If the MAP sensor is defective, then the voltage value will stay stuck at one number no matter how much you accelerate the engine.

5. 5

   If the MAF sensor is bad, you won't get any voltage reading or you'll see one that spikes up and down on its own and that doesn't correspond with you revving up or down the engine.

Let's interpret your multimeter test results:

CASE 1: The multimeter registered a smooth and linear voltage as you revved up and down the engine: this result confirms that the MAF sensor is OK and working like it should.

If the MAF sensor were defective, the output voltage would have stayed stuck in one number no matter how much you revved the engine.

CASE 2: Multimeter DID NOT register the indicated Volts: Recheck all of your test connections and repeat the test. If still the MAF sensor does not behave as indicated, then now you know that it's bad and needs to be replaced.