MAF Sensor Test 2.0L Escort, Tracer (1997-2002)

TEST 3: Testing The 2nd Ground Circuit

In this test section, we're gonna' make sure that the fuel injection computer is providing a 2nd Ground to the mass air flow sensor.

This 2nd Ground is fed to the MAF sensor by the wire labeled with the letter C in the photo above.

NOTE: This 2nd Ground (called the Sensor Return Ground) is provided internally by the fuel injection computer, which means you have to be careful and not short this wire (circuit) to power (12 Volts), or you'll fry the PCM. Be careful.

Let's get started:

1. 1

   Turn key to the OFF Position.

2. 2

   Place the multimeter in Volts DC mode.

3. 3

   With the black multimeter test lead and a wire-piercing-probe, probe the MAF sensor connector's circuit identified with the letter C in the photo.

4. 4

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

5. 5

   Turn the ignition switch to the RUN position.

6. 6

   The multimeter should register battery voltage (10 to 12 Volts).

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

CASE 1: The multimeter registered 10 to 12 Volts. This is the correct test result and tells you that the fuel injection computer is providing Ground.

The next and last test is to check the MAF signal. Go to: TEST 4: Testing The MAF Signal.

CASE 2: The multimeter DID NOT register 10 to 12 Volts. This test result confirms that the MAF sensor is not getting the Ground it needs to function (from the fuel injection computer).

You can also conclude that the MAF sensor is not the problem. Without this computer provided Ground, the MAF sensor will not work. The next step is to find out why this Ground is missing and restore it.

TEST 4: Testing The MAF Signal

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

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.

Remember, as you rev the engine, the MAF sensor should produce and increasing voltage value on your multimeter. This voltage value should go back down when the engine returns to idle.

If the MAF sensor is bad on your Ford Escort, your multimeter is going to show a voltage value that stays stuck at a specific number no matter how much you rev the engine

NOTE: The MAF sensor on your Ford Escort (Mercury Tracer) must be connected to its connector to perform this test. You'll need to use a wire-piercing probe on the wire to access the MAF signal. You can see an example of this tool here: Wire-Piercing Probe.

These are the test steps:

1. 1

   Turn the key to the OFF position.

2. 2

   With a suitable tool connected to the red multimeter test lead, probe the letter D circuit of the MAF sensor connector shown in the photo.

3. 3

   Place the multimeter in Volts DC mode.

4. 4

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

5. 5

   Start the already warmed up engine.

6. 6

   Note the Volts reading on your multimeter at idle.
   
   This voltage reading usually hovers somewhere around 0.9 to 1 Volt DC. 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.

7. 7

   Accelerate the engine (by manually opening the throttle) as you watch the multimeter's voltage readings.
   
   At about 1500 RPMs you'll see about 1.4 Volts DC.
   
   At around 2500 RPMs the multimeter should register around 1.8 Volts DC.
   
   The actual voltage reading on your multimeter may/will vary slightly.

8. 8

   The voltage numbers should correspond to the amount of acceleration.

9. 9

   Now, when you close the throttle and the engine returns to idle, the multimeter should display the voltage value that you observed in test step 6 (about 0.9 to 1 Volt DC).

10. 10

    Repeat this as often as you need to verify that the voltage numbers on the multimeter rise smoothly every single time.

11. 11

    If the MAF sensor is good, these readings will not spike up and down crazily but will correspond to the amount of air the engine is breathing at the different RPMs you're accelerating the engine to.

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

CASE 1: The signal voltage increased/decreased as you manually opened/closed the throttle. This result confirms that the MAF sensor on your Escort or Tracer is functioning correctly.

If the MAF sensor were defective, your multimeter who would've shown a voltage of value that would've stayed stuck at a specific number no matter how much you rev the engine.

CASE 2: The signal voltage DID NOT increase/decrease as you manually opened/closed the throttle. This result confirms that the MAF sensor on your Escort or Tracer is bad and needs to be replaced only if you have confirmed that the MAF sensor is getting power and its two Grounds.