How To Test The MAF Sensor (1991-1995 3.0L V6 Ford Taurus, Mercury Sable)

I think you're going to be surprised at how easy it is to test the MAF sensor on your 1991–1995 3.0L V6 Ford Taurus or Mercury Sable. As a matter of fact, you don't need any expensive diagnostic equipment —just a multimeter.

In this tutorial, I'm going to show you the four tests you need to do to find out if it's good or bad.

These four tests include checking the MAF sensor's output signal, making sure it's getting power (VPWR), and confirming it has Ground (PWR GND and MAF RTN).

With your test results, you'll quickly and easily know if the MAF sensor is toast and needs to be replaced or if it's good and the problem lies somewhere else.

APPLIES TO: This tutorial applies to the following vehicles:

• 3.0L V6 Ford Taurus: 1991, 1992, 1993, 1994, 1995.
• 3.0L V6 Mercury Sable: 1991, 1992, 1993, 1994, 1995.

1996-2003 MAF SENSOR TESTS:

• How To Test The MAF Sensor (1996-1999 3.0L V6 Ford Taurus, Mercury Sable).
• How To Test The MAF Sensor (2000-2003 3.0L V6 Ford Taurus, Mercury Sable).

Symptoms Of A Bad MAF Sensor

The MAF sensor is the component that supplies the fuel injection computer with airflow information, and with this data, it's able to calculate the correct amount of air entering the engine.

Once the fuel injection computer knows how much air the engine is pulling in, it can calculate the proper amount of fuel to deliver into the cylinders to keep it running optimally.

Now, because of how critical the MAF sensor is to the engine management system on your Ford Taurus or Mercury Sable, when it fails, the engine is going to resent it —and you'll see 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 on the 1991–1995 3.0L V6 Ford Taurus (or Mercury Sable) uses a 4-wire connector, and each of those wires has a specific job —either delivering a signal to the MAF sensor or carrying one from the sensor to the fuel injection computer.

In the table below, I've included a brief description of what each wire (circuit) does to help us in the diagnostic 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?

To test the MAF sensor on your 1991–1995 3.0L V6 Ford Taurus or Mercury Sable, you'll need two important tools (nothing that's gonna break the bank), and these are:

• 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.

In the links below, I'm recommending the multimeter I've been using for years. It's a solid meter that gets the job done and has all the features needed to test a MAF sensor or any other component on your vehicle.

The wire-piercing probe kit I recommend is another tool I personally use. It's affordable, functional, and can be used either as a wire-piercing probe or as a back probe.

TEST 1: Testing The MAF Signal

As we've already discussed in the previous sections, the MAF sensor's signal is directly tied to the amount of air entering the engine. For example:

• When you're sitting at a traffic light and the engine is idling, engine RPM is low and airflow into the engine is low, so the MAF sensor's voltage signal is also low —around 1 Volt DC.
• Now, when you step on the gas pedal to move the vehicle from that traffic light, airflow increases, RPM goes up, and the MAF sensor's voltage output rises to match what's happening.

Because of this predictable behavior, you and I can tap into the MAF signal wire (the light blue with red stripe wire), check its voltage with a multimeter, and watch what happens as we rev the engine up and down. That's exactly what we're going to do in our first MAF sensor test.

If the MAF sensor is bad, its voltage signal usually stays stuck at one value —no matter the engine speed or airflow.

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 is the correct signal response and confirms the MAF sensor is functioning correctly.

If a code 157 (MAF Signal Below Minimum Voltage) or code 158 (MAF Above Maximum Voltage) is stored, it shows that the condition that triggered the code isn't happening right now —since the signal is responding to RPM changes instead of being stuck too high or too low.

CASE 2: The signal voltage stayed fixed at one value no matter how the engine speed changed. This typically points to a bad MAF sensor.

Before condemning the sensor (and replacing it), we need to do a couple of additional checks. The next step is: TEST 2: Making Sure The MAF Sensor Is Getting Power (VPWR).

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

12 Volts (VPWR) are supplied to your Taurus or Sable's MAF sensor through the red (RED) wire, which connects to female terminal A of the MAF sensor's 4-wire connector.

These 10 to 12 Volts are present at terminal A only when the key is in the RUN or START position, and we'll confirm this with a multimeter voltage test.

If power is present at terminal A, we'll move on to TEST 3 to make sure terminal B is delivering chassis Ground to the MAF sensor.

IMPORTANT: Be careful when probing the front of the terminal with your multimeter test leads. If the test lead is too thick, it could permanently open up the terminal. If that happens, you'll need to replace the connector.

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 is the correct and expected result, confirming the sensor is receiving VPWR power.

The next step is to make sure the MAF sensor also has chassis Ground (PWR GND). Go to: TEST 3: Making Sure The MAF Sensor Is Getting Ground (PWR GND).

CASE 2: The multimeter did not show 10 to 12 Volts. Recheck your multimeter connections and repeat the test to verify.

If voltage is still missing, the MAF sensor itself isn't the issue —it simply can't work without a proper 10 to 12 Volt feed.

Your next step is to track down why the RED wire is missing this VPWR voltage and fix it, so the MAF sensor can function correctly and clear the diagnostic trouble code (DTC).

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

The MAF sensor's hot wires not only need 12 Volts (VPWR), but they also need chassis Ground (PWR GND) to do their job.

The wire that provides this chassis Ground is the black with light green stripe (BLK/GRN) wire of the MAF sensor's 4-wire connector.

To check for Ground in the BLK/LT GRN wire, we're gonna do a simple multimeter voltage test at terminal B of the connector.

Keep in mind that this chassis Ground is always available at terminal B —whether the key is in the OFF, RUN, or START 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 3 should match up with the BLK/LT GRN wire at 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. This is the correct result and confirms the MAF sensor has chassis Ground (PWR GND).

For our next —and final— step, we'll verify that the fuel injection computer is also supplying sensor Ground (MAF RTN) to the MAF sensor. Go to: TEST 4: Making Sure The MAF Sensor Is Getting Ground (MAF RTN).

CASE 2: The multimeter does not show 10 to 12 Volts. This tells you the MAF sensor isn't getting chassis Ground.

Recheck your test connections and repeat the test. If the 10 to 12 Volt reading is still missing, you can rule out the MAF sensor itself —since it cannot function without this PWR GND Ground on the BLK/LT GRN wire.

Your next troubleshooting step is to locate the cause of the missing chassis Ground and fix it.

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

OK, up to this point you have tested and confirmed that:

• The MAF signal is stuck at one value no matter how much you rev the engine up or down (TEST 1).
• The RED wire is supplying 10 to 12 Volts (TEST 2).
• The BLK/LT GRN wire is providing chassis Ground (TEST 3).

For our last MAF sensor test, we're going to make sure the PCM is supplying the sensor with the MAF RTN Ground —which comes internally from the PCM and is carried by the tan with light blue stripe (TAN/LT BLU) wire.

Like the previous tests, we'll use a simple multimeter voltage check, but this one will be done at terminal C of the MAF connector.

CAUTION: Since the MAF RTN Ground is provided by the PCM itself, you need to be careful when testing this circuit. Do not apply 12 Volts directly from the battery to it, or you'll fry the PCM. The test I'm describing below is a safe and easy way to check for Ground at terminal C.

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. This confirms the MAF RTN circuit is functioning and the PCM is supplying sensor Ground to the MAF sensor.

If you've confirmed all of the following, then you can be certain the MAF sensor is faulty and needs to be replaced:

• TEST 1 —The MAF signal output voltage remains stuck at one value no matter the engine speed.
• TEST 2 —The RED wire is delivering 10 to 12 Volts (VPWR).
• TEST 3 —The BLK/LT GRN wire is supplying chassis Ground (PWR GND).
• This test —The fuel injection computer is providing MAF RTN Ground.

If you've confirmed the MAF sensor is bad and need to replace it, I want to make you aware that you'll need to buy the MAF sensor specified for your exact year, make, model, and engine size —whether it's the 12-valve OHV, the 24-valve DOHC, or the flex-fuel version.

For the most part, these sensors are not interchangeable between engines, even if they look the same. Also, if your MAF sensor is gray, replace it with a gray one; if it's black, replace it with the same.

Otherwise, even though the connector plugs in, the wrong sensor will cause major engine performance problems once you start the engine and attempt to drive the vehicle.

CASE 2: The multimeter did not show 10 to 12 Volts. This means the MAF sensor isn't getting a MAF RTN Ground from the fuel injection computer.

Recheck your multimeter connections and repeat the test. If it still doesn't display 10 to 12 Volts, then the MAF sensor isn't the cause of the trouble code —because it can't operate without the MAF RTN Ground supplied by the your Taurus or Sable's FI computer.

Your next step is to diagnose the cause of this missing MAF RTN Ground and repair it.

More 3.0L V6 Ford Taurus Diagnostic Tutorials

You can find a complete list of 3.0L V6 Ford Taurus and Mercury Sable diagnostic tutorials in this index:

• 3.0L V6 Ford Taurus Index Of Articles.

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

• How To Test The TPS -1994-1995 3.0L Ford Taurus.
• How To Test The Fuel Injectors (1991-1995 3.0L Ford Taurus).
• How To Test For A Blown Head Gasket (1990-2007 3.0L V6 Ford Taurus, Mercury Sable).
• How To Do And Interpret An Engine Compression Test (1990-2007 3.0L V6 Ford Taurus, Mercury Sable).