How To Test The MAF Sensor (1998-2003 2.0L DOHC Ford Escort ZX2)

The mass airflow (MAF) sensor on the 1998-2003 2.0L DOHC Ford Escort ZX2 is a 6-wire sensor (since the intake air temp sensor is integrated into it).

Still, testing the MAF sensor portion of the sensor assembly is a piece of cake and can be done with a multimeter (no scan tool required).

In this guide, I'm going to show you how to check it by performing four specific tests: verifying the MAF signal output voltage, confirming it's receiving power (VPWR), and making sure both Grounds (PWR GND and MAF RTN) are solid.

Even though the MAF sensor is mounted inside the round air filter canister assembly (not sitting out in plain view), it's still very easy to test it and determine if it's good or bad.

You can find this tutorial in Spanish here: Cómo Probar El Sensor MAF De 2.0L Ford Escort, Mercury Tracer (at: autotecnico-online.com).

APPLIES TO: This tutorial applies to the following vehicles:

• 2.0L DOHC Ford Escort ZX2: 1998, 1998, 1999, 2000, 2001, 2002, 2003.

1997-2002 2.0L SOHC ESCORT/TRACER MAF SENSOR TEST:

• How To Test The MAF Sensor (1997-2002 2.0L SOHC Ford Escort, Mercury Tracer).

Common Symptoms Of A Bad Ford MAF Sensor

The MAF sensor is the main sensor your PCM relies on for figuring out how much air is flowing into the engine, and from that, it's calculating how much fuel needs to be injected into the cylinders.

When the MAF sensor starts failing (or has failed), you're going to see the check engine light illuminated on the dash, and your Escort ZX2 may also show one or more of the following symptoms:

• MAF trouble codes that light up the check engine light (CEL) on your instrument cluster.
  • P0102: MAF Signal Low Input to PCM.
  • P0103: MAF Signal High Input to PCM.
• MAF sensor malfunction that DOES NOT light up the check engine light (CEL).
• Lean and/or Rich code(s).
• Fuel trim code(s).
• A tremendous lack of power upon acceleration.
• Black smoke coming from the tail-pipe.
• Bad gas mileage.
• Vehicle may idle rough and stall.

Circuit Descriptions Of The Ford MAF Sensor's Connector

The MAF sensor on your Ford Escort ZX2 has a 6-wire connector. In the table below, I've broken down what each circuit is responsible for so you'll know exactly what you're testing in the steps that follow.

Pin	Wire	Description
2	Red (RED)	VPWR –12 Volts Input in RUN or START
3	Black with white stripe (BLK/WHT)	PWR GND –Chassis Ground Input
4	Tan with light blue stripe (TAN/LT BLU)	MAF RTN –MAF sensor Ground (provided by PCM)
5	Light blue with red stripe (LT BLU/RED)	MAF –MAF signal

IMPORTANT: All of the tests are ON CAR TESTS, do not remove the mass airflow sensor from the vehicle or from its plumbing.

TEST 1: Testing The MAF Signal

The first thing we'll do, to figure out if the MAF sensor is good or bad, is to tap into the light blue with red stripe (LT BLU/RED) wire —this is the MAF signal output wire— with your multimeter and watch how the sensor reacts to engine airflow.

As you run this MAF signal test, here's what you should see:

• When you rev the engine and airflow increases, the MAF signal voltage should climb right along with it.
• When you let off the throttle and engine RPMs drop, the MAF signal voltage should fall as the airflow decreases.

No matter how many times you rev the engine and then let it return to idle, the MAF signal should always rise with RPM and drop back down once it settles at base idle.

If the MAF sensor on your Ford Escort ZX2 is failing (or has failed), that signal voltage will stay stuck at one value no matter how much you rev the engine up or down.

NOTE: The MAF sensor needs to stay connected to its engine wiring harness connector while you test the MAF signal. This means you'll need to pierce the MAF signal wire with a wire-piercing probe. If you don't have one, here's the exact one I use and recommend: Goupchn 4mm Banana to Banana Plug Test Leads Kit (Amazon affiliate link)..

These are the test steps:

1. 1

   Switch your multimeter to Volts DC.

2. 2

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

3. 3

   Connect the red lead to the light blue with red stripe (LT BLU/RED) wire using a wire-piercing probe.
   
   This LT BLU/RED wire is labeled with the number 5 in the image above.

4. 4

   Start the engine and let it idle.
   
   Once idle smooths out, note the voltage reading on the multimeter. A little fluctuation is normal. This first reading is your base MAF signal voltage.

5. 5

   Rev the engine by opening the throttle.
   
   You can do this at the throttle body by moving the linkage, or by having a helper step on the accelerator pedal.

6. 6

   The MAF signal voltage should rise as RPM increases.

7. 7

   Release the throttle to let the RPM come back down.

8. 8

   The voltage should drop as the RPMs fall.

9. 9

   Repeat the accelerate/release cycle a few times to verify the results are consistent.

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

CASE 1: The signal voltage rises and drops as you open and close the throttle by hand. That confirms the MAF sensor on your Escort ZX2 is working the way it should.

If the MAF sensor were failing (or toast), your multimeter would show a voltage that stays stuck at one number no matter how much you rev the engine up or let it come back down.

CASE 2: The signal voltage does NOT rise or drop as you open and close the throttle. That's not a good sign. It could point to a bad MAF sensor, but it could also mean the sensor isn't receiving power or Ground.

Before you condemn the MAF sensor, you need to check that it's getting power and Ground. Head over to: TEST 2: Making Sure The MAF Is Getting VPWR.

TEST 2: Making Sure The MAF Is Getting VPWR

As you probably already know, the MAF sensor on your Escort ZX2 is a hot-wire type, and those hot wires have to get 12 Volts to do their job.

In this test, you'll make sure the sensor actually receives that voltage. To do it, you'll disconnect the MAF sensor from its engine wiring harness connector.

With your multimeter, the next step is to check that terminal 2 of the engine harness connector (the male side) shows 10 to 12 Volts with the key turned to RUN (but with the engine OFF).

NOTE: The MAF sensor connector on the engine harness side uses round male terminals and should match the illustration in the connector pinout diagram above.

Alright, these are the test steps:

1. 1

   Disconnect the MAF sensor from its engine wiring harness connector.

2. 2

   Put your multimeter in Volts DC mode.

3. 3

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

4. 4

   Gently probe round male terminal number 2 with the red multimeter lead.
   
   Terminal 2 should connect to the RED wire on the MAF sensor's engine wiring harness connector.

5. 5

   Turn the key to the RUN position, but don't crank or start the engine.

6. 6

   The multimeter should display 10 to 12 Volts.

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

CASE 1: Your multimeter shows 10 to 12 Volts. That's the correct result, and it confirms the MAF sensor's VPWR circuit is doing its job.

From here, the next thing you need do is check that the MAF sensor is also receiving chassis Ground (PWR GND) at terminal 3. To run that check, go to: TEST 2: Making Sure The MAF Is Getting PWR GND (Chassis Ground).

CASE 2: Your multimeter does NOT show 10 to 12 Volts. That result tells you the MAF sensor isn't receiving power.

This test result also confirms the MAF sensor itself isn't the cause of the problem. Without that 12 Volt feed in place, the sensor can't function at all.

Your next move is to track down why the VPWR feed is missing and get it restored to the circuit.

TEST 3: Making Sure The MAF Is Getting PWR GND (Chassis Ground)

Now that you've confirmed the MAF sensor's hot wires are receiving VPWR power, the next step is to make sure they also getting a solid Ground.

This particular Ground is a chassis Ground, and Ford refers to it as the PWR GND. Because it's tied to the chassis, it's always available to the sensor —no matter if the key is in OFF, RUN, or START.

In other words, at terminal 3 you should always find this chassis Ground present, regardless of ignition switch position.

You'll verify it by running a simple voltage test with your multimeter at terminal 3, thus checking that the black (BLK) wire is actually delivering a good solid path to chassis Ground.

This is what you'll do:

1. 1

   Unplug the MAF sensor from its engine wiring harness connector.

2. 2

   Set your multimeter to Volts DC.

3. 3

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

4. 4

   Probe round male terminal number 3 with the black multimeter lead.
   
   Terminal 3 should correspond to the BLK wire at the MAF sensor's engine wiring harness connector.

5. 5

   Your multimeter should show between 10 and 12 Volts.
   
   NOTE: Because this is a chassis Ground, it will always be present, whether the key is ON or OFF.

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

CASE 1: Your multimeter shows 10 to 12 Volts. That's the correct result, and it tells you the MAF sensor does have a solid chassis Ground.

The next (and last) thing you'll do is check that the sensor is also receiving its MAF RTN Ground from the PCM. To run that check, head over to: TEST 4: Making Sure The MAF Is Getting MAF RTN Ground.

CASE 2: Your multimeter does NOT show 10 to 12 Volts. That confirms the MAF sensor isn't getting the chassis Ground it needs to function.

With this test result, you can also rule out the sensor itself as bad. Without a chassis Ground connection on this circuit, the MAF sensor can't work at all. Your next step is to track down why that Ground is missing and restore it.

TEST 4: Making Sure The MAF Is Getting MAF RTN Ground

So far, your MAF sensor tests have shown:

• The MAF signal output is stuck at one value no matter how you rev the engine (TEST 1).
• The sensor is receiving VPWR power (TEST 2).
• The sensor has a solid chassis Ground (PWR GND) connection (TEST 3).

For the last check, you'll make sure the PCM itself is supplying the MAF sensor with a MAF sensor Ground.

This Ground is generated internally by the PCM and is referred to as the MAF RTN Ground.

To verify it, you'll do a simple multimeter voltage test at male terminal 4. The wire that connects to this terminal is the tan with light blue stripe (TAN/LT BLU) wire coming out of the connector.

NOTE: Because this Ground comes directly from the PCM, be careful to not apply battery voltage to this circuit. Doing so will deep-fry the PCM. One safe way to confirm the presence of this MAF RTN Ground is with a multimeter voltage test I'm outlining below.

Let's get started:

1. 1

   Disconnect the MAF sensor from its electrical connector.

2. 2

   Place your multimeter in Volts DC mode.

3. 3

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

4. 4

   Probe male terminal number 4 with the black multimeter test lead.
   
   Terminal number 4 should correspond to the TAN/LT BLU wire of the MAF sensor connector.

5. 5

   Turn the key to the RUN position but don't crank or start the engine.

6. 6

   You should see 10 to 12 Volts on the multimeter.

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

CASE 1: Your multimeter shows 10 to 12 Volts. That's the correct result, and it confirms your Escort ZX2's PCM is supplying the MAF RTN Ground the sensor needs.

You can conclude that the MAF sensor itself is bad and needs to be replaced —but only if you've confirmed all of the following:

• TEST 1 →The MAF signal voltage stays stuck at one value no matter how much you rev the engine.
• TEST 2 →You've verified the sensor is getting VPWR (10 to 12 Volts).
• TEST 3 →You've confirmed that the sensor has a solid PWR GND (chassis Ground) connection.
• And in this step, you've verified the PCM is providing the MAF RTN Ground to the sensor.

CASE 2: Your multimeter does NOT show 10 to 12 Volts. This result confirms the MAF sensor isn't getting the computer-supplied Ground it must have in order to function.

You can also rule out the MAF sensor itself as the issue. Without that PCM-provided Ground in place, the sensor can't operate. Your next move is to troubleshoot why this Ground is missing and restore it.

More 2.0L Ford Escort And Mercury Tracer Diagnostic Tutorials

You can find a complete list of 2.0L Ford Escort and Mercury Tracer tutorials in this index:

• 2.0L Ford Escort Index Of Articles.

Here's a small sample of the tutorials you'll find in the index:

• How To Test Engine Compression (1997-2003 2.0L Ford Escort, Mercury Tracer).
• Common Causes Of Spark Plug Failure (1997-2003 2.0L Ford Escort, Mercury Tracer).
• How To Test For A Blown Head Gasket (1997-2003 2.0L Ford Escort, Mercury Tracer).
• How To Test The Throttle Position Sensor (1998-2003 2.0L Ford Escort ZX2).