How To Test The MAF Sensor (1991-1995 3.8L V6 Ford Taurus, Mercury Sable)

The mass air flow (MAF) sensor on your 1991–1995 3.8L V6 Ford Taurus or Mercury Sable isn't difficult to test —and the best part is, you can do it with a simple multimeter. Yep, no scan tool or fancy diagnostic equipment required.

In this tutorial, I'm going to show you how to check the following:

• The MAF signal
• That it's getting VPWR power
• That it's getting both of its grounds — PWR GND and MAF RTN

With your test results, you'll be able to quickly determine if the MAF sensor is good or bad and needs to be replaced.

APPLIES TO: This tutorial applies to the following vehicles:

• 3.8L V6 Ford Taurus: 1991, 1992, 1993, 1994, 1995.
• 3.8L V6 Mercury Sable: 1991, 1992, 1993, 1994, 1995.

TPS DIAGNOSTIC TESTS:

• How To Test The TPS With A Multimeter (1990-1995 3.8L V6 Taurus, Mercury Sable).

Symptoms Of A Bad MAF Sensor

The powertrain control module (PCM) in your 3.8L V6 Ford Taurus needs to know how much air is entering the engine as it runs. And you guessed it —the MAF sensor is the one responsible for this important job.

So when it fails, engine performance is gonna take a hit. You'll notice one or more of the following symptoms:

• Check Engine Light: The CEL will be lit on the dash, and the computer will usually store one of these OBD-I diagnostic trouble codes (DTCs):
  • 157: MAF Sensor Circuit Below Minimum Voltage.
  • 158: MAF Sensor Circuit Above Maximum Voltage.
  • 159: MAF Higher Or Lower Than Expected.
• Lack of power: Your Taurus or Sable's engine may feel weak or hesitate when you hit the gas, especially under load or at higher speeds.
• Rough idle/stalling: The engine can idle unevenly or shut off on its own.
• Bad gas mileage: A bad MAF affects the PCM's ability to control the air-fuel mixture, making the engine run rich or lean, which kills gas mileage.
• Black exhaust smoke: If the PCM is adding too much fuel because of a bad MAF sensor signal, you may see black smoke coming out of the tailpipe.
• Hard starting: Sometimes the engine will crank but struggle to start.
• Hesitation or surging: You might feel the engine stumble or surge while accelerating or cruising.

MAF Sensor Circuit Descriptions

The MAF sensor has four wires coming out of its connector, and each one serves a specific purpose. In the table below, you'll find a brief description of each wire (circuit) —information we'll be using in the tests that follow.

Pin	Wire	Description
A	Red (RED)	VPWR –12 Volts Input in RUN or START
B	Black with light green stripe (BLK/LT GRN)	PWR GND –Chassis Ground Input
C	Tan with light blue stripe (TAN/LT BLU)	MAF RTN –MAF sensor Ground (provided by PCM)
D	Light blue with red stripe (LT BLU/RED)	MAF –MAF signal

What Tools Do I Need To Test The MAF Sensor?

As I mentioned at the beginning of this tutorial, you don't need any expensive or fancy diagnostic equipment to check whether the MAF sensor is good or bad. Here's what you'll need:

• A multimeter: To check the MAF signal voltage output, and verify power and Ground to the sensor.
• A wire-piercing probe or back probe: This tool lets you access the MAF signal voltage inside the MAF signal wire in TEST 1.

If you don't have a multimeter or a wire-piercing probe kit, in the links below, I'm gonna recommend the same tools I personally use. They're reliable, affordable, and will help you get the job done:

TEST 1: Testing The MAF Signal

To get started with our MAF sensor diagnostic, we're going to check its signal voltage output. To understand our results, we need to keep two important things in mind:

1. At idle RPM, the engine breathes in less air. As a result, the MAF sensor produces a low voltage signal —usually around 0.4 to 0.6 Volts DC.
2. When engine RPM increases, airflow into the engine also increases (like when you step on the gas pedal). Consequently, the MAF sensor's signal voltage output also increases (1.4 - 2.0 Volts).

This behavior is very predictable, which allows us to tap into the MAF signal output wire with our multimeter and watch what happens. As we rev the engine up and down, the signal voltage should rise and fall with engine RPM.

When the MAF sensor has failed, the signal voltage usually stays stuck at one value —no matter how much you rev the engine up or down.

IMPORTANT: To check the MAF signal output, the sensor has to remain connected to its 4-wire connector. This means that you'll need to use a back probe on the connector or a wire piercing probe on the wire to be able to read the MAF signal output voltage. If you don't have the appropriate tool, this is the one I use and recommend for these types of tests: Goupchn 4mm Banana to Banana Plug Test Leads Kit (Amazon affiliate link).

Here's the procedure:

1. 1

   Set your multimeter to Volts DC mode.

2. 2

   Attach the black lead of the multimeter to the battery's negative (-) post.

3. 3

   Probe the light blue with red stripe (LT BLU/RED) wire with the red multimeter lead using either a back probe or a wire-piercing probe.
   
   The LT BLU/RED wire connects to terminal D of the MAF sensor connector (see diagram above).

4. 4

   Start the engine and let it idle.
   
   Once the idle steadies out, take note of the reading on the multimeter. Some small fluctuation is normal. This value is your base MAF signal voltage.

5. 5

   Increase engine speed by opening the throttle.
   
   You can do this directly at the throttle body by moving the linkage, or by having a helper press the accelerator pedal.

6. 6

   The MAF signal voltage should climb as RPM rises.

7. 7

   Let go of the throttle so the RPM drops back down.

8. 8

   The signal voltage should decrease as RPM falls.

9. 9

   Repeat the rev-up/release cycle a few times to make sure the readings are consistent.

Here's what your test results mean:

CASE 1: The signal voltage rose as engine speed went up and dropped back down when you released the throttle. This test result tells us that the MAF sensor is functioning properly, since the signal output voltage is reacting to changes in engine RPM.

If either a code 157 (MAF Signal Below Minimum Voltage) or a code 158 (MAF Signal Above Maximum Voltage) is stored in the PCM's memory, then whatever triggered the code isn't happening right now —because the signal isn't stuck; it's responding to RPM increases and decreases.

CASE 2: The signal voltage stayed fixed at one value no matter how the engine speed changed. This usually means the MAF sensor on your Taurus or Sable is toast.

To be absolutely sure the sensor is bad and needs to be replaced, we now need to confirm that it's getting power and both of the grounds it needs to function. For the first of these three tests, head over to: TEST 2: Making Sure The MAF Sensor Is Getting Power (VPWR).

TEST 2: Making Sure The MAF Sensor Is Getting Power (VPWR)

Now that you've confirmed the MAF sensor's signal voltage stays stuck at one value regardless of engine RPM, our next step is to make sure it's getting VPWR power.

This VPWR power comes in the form of 10 to 12 Volts DC and is delivered to terminal A of the MAF sensor connector through the red (RED) wire.

This voltage is only available at terminal A when the key is in the RUN or START position. For our test, we'll check for this voltage with the key in the RUN position but with the engine OFF.

NOTE: There's a good chance the metal probe of your multimeter test lead might be a bit too thick to safely fit into the female terminal of the connector. If that's the case, be very careful when probing to avoid damaging either the terminal or the connector. If any damage occurs, you'll need to replace the entire connector with a new one.

Let's begin:

1. 1

   Unplug the MAF sensor from its electrical connector.

2. 2

   Set your multimeter to Volts DC.

3. 3

   Attach the black multimeter lead to the battery's negative (-) post.

4. 4

   Carefully probe female terminal number A with the red multimeter lead.
   
   Terminal A should correspond to the RED wire on the MAF sensor's 4-wire connector.

5. 5

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

6. 6

   The multimeter should read between 10 and 12 Volts.

Here's how to read your results:

CASE 1: The multimeter showed 10 to 12 Volts. This test result confirms that the MAF sensor's hot wires are getting the power they need.

Now that we've verified VPWR power is being supplied to the sensor, our next step is to make sure the hot wires have a good, solid connection to Ground (PWR GND). For this test, head over to: TEST 3: Making Sure The MAF Sensor Is Getting Ground (PWR GND).

CASE 2: The multimeter did not show 10 to 12 Volts. Double-check your test connections and make sure you're probing the terminal connected to the RED wire, then repeat the test.

If you still don't see 12 Volts of VPWR power at terminal A, you can rule out the MAF sensor itself as bad or as the cause of the MAF trouble codes —because without this voltage, it simply can't function.

Although it's beyond the scope of this tutorial, your next step is to determine why VPWR power is missing from the RED wire and restore it to the circuit. Once VPWR power is restored, the MAF sensor should function normally again, and the MAF code should clear.

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

Your Taurus or Sable's MAF sensor also needs a solid path to chassis Ground for its hot wires to function properly. Since you've already confirmed it's getting VPWR power, our next test is to make sure this chassis Ground (PWR GND) path is good.

The wire that provides this PWR GND Ground to the hot wires is the black with light green stripe (BLK/LT GRN) wire, which connects to terminal B of the sensor's 4-wire connector.

To check for this PWR GND chassis Ground, we'll do a simple multimeter voltage test at terminal B.

One more thing —since this is a chassis Ground, it's available at all times, regardless of the ignition key's position.

IMPORTANT: Be careful when probing the front of the connector or female terminal with the multimeter test lead.

Alright, let's begin:

1. 1

   Disconnect the MAF sensor from its electrical connector.

2. 2

   Switch your multimeter to Volts DC.

3. 3

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

4. 4

   Lightly probe female terminal B with the black lead of the multimeter.
   
   Terminal B should connect to the BLK/LT GRN wire of the MAF sensor connector.

5. 5

   The multimeter should read between 10 and 12 Volts.
   
   NOTE: Since this is a chassis Ground, it'll be present at all times —whether the key is OFF, RUN, or START.

Here's how to interpret your readings:

CASE 1: The multimeter shows 10 to 12 Volts. Good —this indicates that the MAF sensor is getting chassis Ground.

For our final MAF sensor test, we're going to make sure the PCM is supplying the MAF RTN Ground to the sensor. This is another simple test we'll perform with our multimeter. Head over to: TEST 4: Making Sure The MAF Sensor Is Getting Ground (MAF RTN).

CASE 2: The multimeter does not show 10 to 12 Volts. Double-check that you're testing the terminal connected to the BLK/LT GRN wire and repeat the test.

If PWR GND Ground still isn't available at terminal B, we can conclude that the MAF sensor itself is OK and not the cause of the MAF trouble code —because without this chassis Ground, its hot wires won't function.

Although it's beyond the scope of this tutorial to troubleshoot why this chassis Ground is missing, your next step is to find out what's causing the loss of Ground and restore it to the BLK/LT GRN wire. Once the MAF sensor is receiving chassis Ground at terminal B, it'll function normally again, and the MAF code should clear.

TEST 4: Making Sure The MAF Sensor Is Getting Ground (MAF RTN)

Your previous three tests have confirmed the following:

• TEST 1: The MAF signal is stuck at one value regardless of engine RPM increases or decreases.
• TEST 2: The MAF sensor is getting VPWR power at terminal A.
• TEST 3: Terminal B is providing the PWR GND Ground the sensor needs.

In this final test section, we're going to make sure your Taurus or Sable's PCM is providing the MAF RTN Ground the sensor needs.

This MAF RTN Ground is delivered to terminal C by the tan with light blue stripe (TAN/LT BLU) wire of the sensor's 4-wire connector.

Since this is a PCM-supplied Ground, it's only available when the key is in the RUN or START position. For our test, we'll check it with the key in the RUN position but with the engine OFF.

IMPORTANT: Since the MAF RTN Ground is supplied internally by the PCM, you've got to be very careful not to intentionally or accidentally connect this circuit to battery voltage. Doing so will deep fry the PCM. The multimeter voltage test outlined below is a safe and reliable way to check for the presence of this Ground in the circuit.

OK, these are the test steps:

1. 1

   Unplug the MAF sensor from its connector.

2. 2

   Set your multimeter to Volts DC.

3. 3

   Attach the red multimeter lead to the battery positive (+) post.

4. 4

   Carefully probe female terminal C with the black multimeter lead.
   
   Terminal C should match up with 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

   The multimeter should register between 10 and 12 Volts.

Here's how to interpret your readings:

CASE 1: The multimeter showed 10 to 12 Volts. Great! This test result confirms that the MAF sensor is getting the MAF RTN Ground from the PCM.

Based on the results of your previous three MAF sensor tests, you can now conclude that the sensor is bad and needs to be replaced if you've confirmed the following:

• TEST 1: The MAF signal voltage output is stuck and does not react to engine RPM increases or decreases.
• TEST 2: The sensor is getting VPWR power.
• TEST 3: The sensor is getting PWR GND chassis Ground.
• TEST 4: The PCM is providing the MAF RTN Ground.

CASE 2: The multimeter did not show 10 to 12 Volts. Make sure you're testing the correct terminal —the one that connects to the TAN/LT BLU wire— and repeat the test.

If you still don't see the MAF RTN Ground present at terminal C, then we can conclude that the MAF sensor itself is OK and not the cause of the MAF trouble code lighting up the check engine light. Without this MAF RTN Ground, the sensor simply won't function.

Although it's beyond the scope of this tutorial, your next step is to determine why this PCM-supplied Ground is missing and restore it to the circuit. The most likely cause of this missing MAF RTN Ground is an open-circuit in the TAN/LT BLU wire between the MAF sensor connector and the PCM.

More 3.8L V6 Ford Taurus Diagnostic Tutorials

You can find a complete list of diagnostic tutorials for the 3.8L V6 Ford Taurus and Mercury Sable in this index:

• 3.8L V6 Ford Taurus Index Of Articles.

Here's a sample of the tutorials you'll find for the 3.8L Ford Taurus (Mercury Sable):

• How To Test The TPS With A Multimeter (1990-1995 3.8L V6 Taurus, Mercury Sable).
• How To Test The Fuel Pump (1990-1995 3.8L V6 Ford Taurus, Mercury Sable).
• How To Test The Engine Compression (1990-1995 3.8L V6 Ford Taurus, Mercury Sable).
• How To Test For A Blown Head Gasket (1990-1995 3.8L V6 Ford Taurus, Mercury Sable).