## TEST 3: Testing The 5 V Reference Signal

So far you've made sure that the MAF sensor has battery power and Ground. The next step is to make sure it's getting a 5 Volt reference voltage signal from the fuel injection computer.

The wire that delivers these 5 Volts DC to the MAF sensor is the red (RED) wire of the MAF sensor harness connector.

These are the test steps:

1. 1

Probe the red wire of the MAF sensor connector that is identified with the number 2 in the photo with the red multimeter test lead.

2. 2

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

3. 3

Place your multimeter in Volts DC mode and turn the key on (but don't crank or start the engine).

4. 4

The multimeter should display 4.5 to 5 Volts DC.

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

CASE 1: The multimeter registered 5 Volts. This test result tells you the circuit is OK and the computer is doing its job. The next step is to verify that the Maxima's mass air flow sensor is creating a MAF signal the computer can use. For this test go to: TEST 4: Testing The MAF Signal.

CASE 2: The multimeter DID NOT register 5 Volts. This test result means you must find the cause of these missing 5 Volts. Without this voltage the MAF sensor will not function.

## TEST 4: Testing The MAF Signal

In this last test, we're gonna' test the MAF signal itself with a multimeter.

If the MAF sensor is functioning correctly, then it should produce a low voltage signal at engine idle that should increase as you rev the engine up.

If the MAF is fried, then the voltage signal will stay stuck in one value no matter how much you rev up the engine.

The wire that carries the MAF signal is the white (WHT) wire of the MAF electrical connector.

OK, let's get started:

1. 1

Probe the white (WHT) wire that's identified with the number 1 in the photo with the red multimeter test lead.

2. 2

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

3. 3

Put the multimeter in Volts DC mode and crank and start the engine. If the engine is completely cold, let it warm up before the next step.

4. 4

At engine idle, you should see about 1.2 Volts on your multimeter. Now, this reading may be stable (with only small fluctuations) or unstable with very large fluctuations. No matter what the instability in the reading, this will be your base voltage reading.

5. 5

Manually accelerate the engine as you observe how the multimeter's voltage value increases. As a reference point, at around 2,500 RPM's you should see about 2.5 Volts.

The higher you accelerate the engine, the higher the voltage reading on your multimeter.

6. 6

You should see the voltage value on the multimeter return to the base voltage value you recorded in step 4. This voltage reading may not be the exact same but should be very close.

7. 7

Rev up/rev down the engine several times as you look for the corresponding increase/decrease in voltage.

8. 8

If the MAF sensor is good, these readings will not spike up and down crazily or stay stuck in one value but will increase/decrease as you rev up/rev down the engine.

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

CASE 1: If the voltage reading increased and decreased as you were revving up/revving down the engine, then the Maxima's MAF sensor is working correctly.

Here's why: If the MAF sensor were faulty, your multimeter's reading would have stayed stuck at one value no matter how much you revved up the engine. Since the value went up as you revved up the engine, then you can consider the MAF sensor working correctly.

CASE 2: If the voltage reading DID NOT increase and decrease as you were revving up/revving down the engine, then the mass air flow sensor on your Nissan Maxima is bad. Replace the MAF sensor.