How To Test The MAF Sensor (1991-1993 2.3L Ford Mustang)

Testing the MAF sensor on the 1991–1993 2.3L Ford Mustang isn't difficult at all. And the best part is, you don't need any expensive diagnostic equipment to get it done.

In this guide, I'm going to show you how to test it at home using a multimeter. We'll run four tests, including a MAF sensor signal output check. If the signal's missing, we'll also make sure it's getting power and Ground.

By the end of these tests, you'll know if the MAF sensor on your 2.3L Ford Mustang is bad 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:

• 2.3L Ford Mustang: 1991, 1992, 1993.

Symptoms Of A Bad MAF Sensor

The fuel injection computer on your 2.3L Ford Mustang needs to know how much air is entering the engine. With this information, it's able to now calculate how much fuel it needs to inject into each cylinder.

And the component that is tasked with providing this info to the computer is the MAF sensor sitting right next to the air filter assembly.

When this bad boy fails, it's going to wreak havoc on the engine since the computer won't know how much fuel to inject and keep it running optimally. You're gonna 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 Mustang'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 1991-1993 2.3L Ford Mustang has four wires coming out of its connector. Each wire has a specific job to do.

Some deliver signals to the MAF sensor, while others carry signals away from it to the PCM. In the table below is a brief description of each circuit, which will help us troubleshoot the sensor 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 in the introduction to this tutorial, you don't need any expensive diagnostic equipment to figure out if the MAF sensor is good or bad. But you'll need two very important tools, and they 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

To successfully diagnose the MAF sensor as good or bad, we need to know that it's designed to react to the amount of airflow entering the engine. For example:

• When airflow is low, engine RPM is low too —like when you're sitting at a traffic light waiting for it to turn green. In this scenario, the MAF sensor outputs around 1 Volt.
• When you step on the gas to move away from that light, airflow into the engine increases and RPM go up. The MAF sensor reacts to the increase in airflow by producing a higher voltage signal.

Because its voltage signal output rises with an increase in airflow and drops with a decrease in airflow, we can check this behavior by tapping into the MAF signal wire —the light blue with red stripe (LT BLU/RED) wire— with our multimeter. Then by revving the engine up and down, we can watch what the signal does. And that's what we'll do for our first test.

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

IMPORTANT: Your Ford Mustang's MAF sensor must remain connected to its 4-wire connector to read its voltage signal output with your multimeter. To access the signal inside the wire, you'll need to either back probe the connector or use a wire-piercing probe on the signal wire itself. If you don't have one, this is the tool 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 climbed as RPM increased and dropped back down once you let off the throttle. This is the proper MAF signal reaction and confirms the MAF sensor on your 2.3L Ford Mustang is working like it should.

If you've got a code 157 (MAF Signal Below Minimum Voltage) or code 158 (MAF Signal Above Maximum Voltage) stored, this result shows the condition that set the code isn't happening right now —since the signal is following RPM/airflow changes instead of being stuck too high or too low.

CASE 2: The signal voltage stayed stuck at the same value no matter how the engine speed changed. This usually means the MAF sensor is toast.

Before calling the sensor bad (and replacing it), we need to run a couple more 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)

The MAF sensor's hot wires require 12 Volts (VPWR) to function, and this voltage comes through the red (RED) wire that connects to female terminal A of the MAF sensor's 4-wire connector.

Another important thing to know is that these 10 to 12 Volts are only present at terminal A when the key is in the RUN or START position, and that's how we'll check it with our multimeter in Volts DC mode.

Once we've confirmed that terminal A has 10 to 12 Volts, the next step is to make sure the hot wires are getting chassis Ground (PWR GND) in TEST 3.

IMPORTANT: Be careful when probing the front of the terminal with your multimeter test leads. If the test lead's metal probe 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 displayed 10 to 12 Volts. That's good news —this confirms the MAF sensor is getting its VPWR power supply.

The next step is to verify that terminal B has a solid chassis Ground (PWR GND). Head over to: TEST 3: Making Sure The MAF Sensor Is Getting Ground (PWR GND).

CASE 2: The multimeter did not display 10 to 12 Volts. Double-check your multimeter test connections and run the test again to be sure.

If the voltage is still missing, then the MAF sensor itself isn't to blame —it simply can't operate without that 10 to 12 Volt power supply.

Your next step is to find out why the RED wire isn't supplying VPWR voltage and repair the issue, so the MAF sensor can work properly and the diagnostic trouble code (DTC) can be cleared.

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

Besides needing 12 Volts, the MAF sensor's hot wires also need chassis Ground (PWR GRN). This is provided by the black with green stripe (BLK/GRN) wire that connects to terminal B of the sensor's 4-wire connector.

In this test section, we're going to do a simple multimeter voltage test on terminal B to confirm the circuit has a good, solid connection to chassis Ground.

Since this is a chassis Ground, it's available at all times. In other words, whether the ignition key is in the OFF, RUN, or START position, this Ground is always present.

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

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: Your multimeter displays 10 to 12 Volts DC at terminal B. Great! This is the correct and expected result, and it tells you that terminal B is delivering chassis Ground to the MAF sensor's hot wires.

Your next and final test is to make sure terminal C is delivering the MAF RTN Ground. For this test, head over to: TEST 4: Making Sure The MAF Sensor Is Getting Ground (MAF RTN).

CASE 2: Your multimeter isn't showing 10 to 12 Volts DC at terminal B. Double-check your multimeter test connections and repeat the test.

If your multimeter still doesn't show 10 to 12 Volts, then you can conclude the MAF sensor isn't getting the chassis Ground it needs for its hot wires to function.

Your next step is to find out why this chassis Ground is missing and restore it to the circuit. Once the BLK/LT GRN wire is delivering chassis Ground to the MAF sensor, it should function again.

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

If you've reached this point, your Ford Mustang MAF sensor tests indicate that:

• The sensor's output voltage signal is stuck at one value no matter how much you rev the engine up or down in TEST 1.
• It's getting 12 Volts (VPWR) in TEST 2.
• The sensor is also getting chassis Ground (PWR GND) in TEST 3.

In this last test section, you're going to make sure terminal C is delivering the MAF RTN Ground, which is provided internally by the fuel injection computer.

This MAF RTN Ground comes through the tan with light blue stripe (TAN/LT BLU) wire of the MAF sensor's 4-wire connector.

To check for the presence of this Ground, we're going to do a multimeter voltage test, just like in the previous three tests.

CAUTION: The MAF RTN Ground is provided by your Mustang's fuel injection computer (it's not a chassis Ground), so be careful when testing this circuit. Do not apply 12 Volts directly from the battery to it, or you'll fry the computer. 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 shows 10 to 12 Volts. This is the correct and expected test result, and it tells you the fuel injection computer is providing the MAF RTN Ground to the MAF sensor through the TAN/LT BLU wire.

If you've confirmed the following, then you can conclude the MAF sensor is bad and needs to be replaced:

• In TEST 1, the MAF output voltage signal is stuck at one value when you rev the engine up and down.
• In TEST 2, the MAF sensor is getting 10 to 12 Volts (VPWR).
• In TEST 3, you've confirmed it's getting chassis Ground (PWR GND).
• In this test, the fuel injection computer is supplying the MAF sensor with the MAF RTN Ground.

If you've confirmed the MAF sensor is bad and need to replace it, I recommend the following two non-knock-off brand MAF sensors. Both are brands that I've used for many years and don't hesitate to recommend:

• Walker Products 245-2016 Mass Air Flow Sensor (Amazon affiliate link).
• Delphi AF10488 Mass Air Flow Sensor (Amazon affiliate link).

CASE 2: The multimeter does not show 10 to 12 Volts. This tells you the MAF sensor isn't being supplied with a MAF RTN Ground by the TAN/LT BLU wire.

Double-check your multimeter test connections and repeat the test. If you still don't see your multimeter displaying 10 to 12 Volts, then the MAF sensor itself is not the cause of the trouble code —because without this MAF RTN Ground, the sensor isn't going to function.

Your next step is to find the cause of the missing MAF RTN Ground and repair it to get the MAF sensor working again.

More 2.3L Ford Mustang Diagnostic Tutorials

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

• 2.3L Ford Mustang Index Of Articles.