How To Test The Throttle Position Sensor (1990-1993 5.0L V8 Ford Mustang)

The throttle position sensor (TPS) on the 1990-1993 5.0L V8 Ford Mustang is a very easy component to test with a multimeter.

No scan tool or any other expensive diagnostic equipment is needed to find out if it's good and doing its job, or if it's toast and needs to be replaced.

In this tutorial, I'm going to show you how to check its voltage output signal and also how to make sure it's getting both power (VREF) and Ground (SIG RTN) from the fuel injection computer.

At the end of these three easy tests, you'll be able to quickly and confidently determine if the TPS is bad and needs to be replaced.

APPLIES TO: This tutorial applies to the following vehicles:

• 5.0L V8 Ford Mustang: 1994, 1995.

1994-1995 TPS DIAGNOSTIC TESTS:

• How To Test The Throttle Position Sensor (1994-1995 5.0L Ford Mustang).

Symptoms Of A Bad Throttle Position Sensor (TPS)

The throttle position sensor (TPS) is a critical component of your Ford Mustang's engine management system, since its job is to track the angle of the throttle plate as it opens and closes.

And as you're probably already aware, the throttle plate is connected to the accelerator pedal via an accelerator cable, and it opens and closes as you step on or off the accelerator pedal.

When the computer doesn't receive information from the throttle position sensor because it's failed, you'll notice one or more of the following engine performance issues:

• Check engine light with TPS codes:
  • Code 23: TPS Out Of Self-Test Range.
  • Code 53: TPS Circuit Above Maximum Voltage.
  • Code 63: TPS Circuit Below Minimum Voltage.
• Hesitation on acceleration: Stumbling or hesitation when you press the gas pedal.
• Loss of power: Intermittent lack of power while accelerating.
• Bad gas mileage: Noticeable drop in gas mileage.
• Hard starting: Engine takes longer than normal to crank and fire up.
• Rough/lopey idle: Idle speed surges up and down instead of staying steady.
• No-start condition: If TPS voltage is stuck high, the engine may not start at all.

What Tools Do I Need To Test The TPS Sensor?

The two tools you'll need are:

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

Below is the multimeter I've relied on for years to do all kinds of diagnostic tests, and it's never let me down. It has everything you need to check the MAF sensor or any other electrical component on your Mustang (or any other vehicle).

I'm also including a wire-piercing probe kit that I use regularly. It's inexpensive, easy to work with, and doubles as both a piercing probe and a back probe when the job calls for it.

TEST 1: Checking The Throttle Position Sensor (TPS) Signal

The very first thing we're going to do is check the TP sensor's output voltage signal with a multimeter. If the sensor is functioning correctly:

• The TPS signal voltage should increase when we open the throttle plate.
• The TPS signal voltage should decrease when we close the throttle plate.

It doesn't matter how many times we open or close the throttle plate, the TPS signal voltage output should increase or decrease accordingly every time.

If the throttle position sensor is bad, its voltage signal output will usually stay stuck at one value, or it'll glitch out as we actuate the throttle plate.

To get the most accurate test result, I suggest you manually open and close the throttle plate from the engine compartment instead of using the gas pedal.

Depending on the specific year of your Mustang, the wire, we're going to tap into with our multimeter is:

• 1990–1993: The dark green with light green stripe (DK GRN/LT GRN) wire.
• 1993: The gray with white stripe (GRY/WHT) wire.

One last thing I want to mention is that the throttle position sensor must remain connected to its engine wiring harness connector to read the TPS signal in the GRY/WHT (or DK GRN/LT GRN) wire.

To do this, you'll need to either use a back probe on the connector or a wire-piercing probe on the wire itself. If you don't have either of these tools, here are the ones I recommend that you can use as a back probe or as a wire-piercing probe:

• Goupchn 4mm Banana to Banana Plug Test Leads Kit (Amazon affiliate link).

Here are the test steps:

1. 1

   Hook up the black test lead of your multimeter to the negative (-) battery post.

2. 2

   Switch your multimeter to DC Volts mode.

3. 3

   Turn the key to the ON position (engine OFF). Do not crank or start the engine.
   
   This step powers up the TPS.

4. 4

   Probe the GRY/WHT (or DK GRN/LT GRN) wire of the TPS connector with the red multimeter lead and an appropriate tool (like a back probe or a wire-piercing probe).
   
   NOTE: Both TPS connectors must stay connected to each other during this test.

5. 5

   With the throttle plate completely closed, the voltage should read between 0.3 and 0.9 Volts DC.
   
   This is your base reading.

6. 6

   Open the throttle plate slowly by hand. The voltage should climb smoothly as the plate opens.

7. 7

   At wide open throttle (WOT), the voltage should be between 3.5 and 4.5 Volts DC.

8. 8

   Close the throttle plate slowly. The voltage should fall back down to the same number you recorded in step 5.
   
   Verify that the closed-throttle reading matches your starting value.

9. 9

   Lightly tap the TPS body with the handle of a screwdriver while opening and closing the throttle plate.
   
   NOTE: Tapping on the sensor should not cause the readings to spike, cut out, or glitch. If it does, the TPS is faulty and must be replaced.

Here's what your readings mean:

CASE 1: The TPS voltage signal rose and fell smoothly with no glitches. That's exactly what you want to see, and it confirms the TPS is doing its job correctly.

This result also shows that your Mustang's TP sensor is receiving both power (VREF) and Ground (SIG RTN). With this confirmation, you don't need to do any of the other two tests.

CASE 2: The TPS voltage signal stayed the same and never changed. In most cases this indicates a bad TPS, but not always.

To be certain, you'll have to run two more checks. Start with this one: TEST 2: Making Sure The TPS Is Getting Power (VREF).

CASE 3: The TPS voltage signal dropped out or glitched when the sensor was tapped. If you see that, the TPS is defective and should be replaced.

TEST 2: Making Sure The TPS Is Getting Power (VREF)

One of the things that can cause the TPS to not produce a variable voltage signal is if it's not receiving 5 Volts from the fuel injection computer.

These 5 Volts, in Ford-speak, are known as the VREF voltage, and they're only available when the key is in the RUN or START position.

The wire that delivers this VREF voltage to the sensor is the orange with white stripe (ORG/WHT) wire of the TP sensor's engine wiring harness connector.

You and I can easily check for the presence of these 5 Volts in the ORG/WHT wire by doing a simple multimeter voltage test on round male terminal 1 (see the connector pinout above), with the key in the RUN position but the engine off.

IMPORTANT: This test is done on the TPS connector with round male terminals, which belongs to the engine wiring harness pigtail connector. The connector coming out of the TP sensor itself has round female terminals.

Here's what we need to do:

1. 1

   Unplug the TPS from its 3-wire connector.

2. 2

   Switch the key to the ON position (engine off). Don't crank or start the engine —this step only powers up the TPS circuit.

3. 3

   Put your multimeter in Volts DC mode.

4. 4

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

5. 5

   Probe male terminal 3 of the TPS connector with the red multimeter lead.
   
   NOTE: Terminal 3 is the 5-Volt supply and should connect to the ORG/WHT wire of the connector.

6. 6

   The multimeter should show between 4.5 and 5.0 Volts DC.

Here's how to interpret your results:

CASE 1: The multimeter reads between 4.5 and 5 Volts. That's the number we want to see, and it confirms the TPS is getting its power feed (VREF).

The next step is to make sure the sensor also has its SIG RTN Ground. You can check that here: TEST 3: Making Sure The TPS Is Getting Ground (SIG RTN).

CASE 2: There's no voltage at all. First, confirm that your meter lead is on the correct terminal and repeat the test.

If the reading is still missing, the problem isn't the TPS itself. Without that 5-Volt supply, the sensor won't function.

Your next step is to find out why the 5 Volts aren't reaching the sensor and fix it so the TPS can work again.

Most of the time, the missing VREF voltage is caused by an open in the ORG/WHT wire between the TPS connector and your Ford Mustang's FI computer.

TEST 3: Making Sure The TPS Is Getting Ground (SIG RTN)

OK, your previous two tests have confirmed the following:

• The TPS signal output voltage is stuck at one value, no matter how much you open or close the throttle plate (TEST 1).
• The sensor is receiving the VREF 5 Volts from the computer (TEST 2).

For our final diagnostic check, we're going to make sure your Mustang's fuel injection computer is providing the SIG RTN Ground.

This SIG RTN Ground is provided by the computer itself (it's not a chassis ground), and it's delivered to the TP sensor through the black with white stripe (BLK/WHT) wire.

To check for the presence of this Ground, we're going to do a multimeter voltage test on male terminal 3 (see the connector pinout above).

IMPORTANT: Be careful with this SIG RTN circuit because the Ground is provided internally by your Mustang's computer. Do not connect this wire to battery 12 Volts, or you'll fry the fuel injection computer. The multimeter voltage test we're about to do is the safe way to verify the presence of this Ground.

OK, let's begin:

1. 1

   Unplug the TPS from its 3-wire connector.

2. 2

   Turn the ignition key to the ON position (engine off). Don't crank or start the engine —this step only powers up the TPS circuit.

3. 3

   Put your multimeter in Volts DC mode.

4. 4

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

5. 5

   Probe male terminal 3 of the TPS connector with the black multimeter lead.
   
   NOTE: Terminal 3 is the Ground circuit and should be the BLK/WHT wire in the TPS connector.

6. 6

   Your multimeter should show between 10 and 12 Volts DC.

Alright, let's find out what your test result means:

CASE 1: Ground is present. That's the outcome we're looking for.

You can conclude the TPS is bad and needs replacement if all of the following are true:

• In TEST 1, the TPS signal voltage stayed the same and never moved with throttle plate movement.
• In TEST 2, the TPS showed it was getting its 5-Volt reference feed.
• In this test, you confirmed the TPS is getting its SIG RTN Ground supply.

CASE 2: Ground is missing. Double-check that your meter lead is on the correct terminal and repeat the test to be sure.

If the multimeter still doesn't display 10 to 12 Volts DC, then the TPS itself isn't to blame. Without a SIG RTN Ground, it just can't work.

The actual repair is outside the scope of this tutorial, but your next step is to track down what's causing the missing Ground and correct it so the TPS can function again.

In most cases, the issue comes from an open in the BLK/WHT wire between the TPS connector and the fuel injection computer.

More 5.0L V8 Ford Mustang Diagnostic Tutorials

You can find a complete list of wiring diagrams and diagnostic tutorials for the 5.0L V8 Ford Mustang in this index:

• 5.0L V8 Ford Mustang Index Of Articles.

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

• How To Test The Fuel Pump (1990-1995 5.0L V8 Ford Mustang).
• How To Test The MAF Sensor (1991-1995 5.0L V8 Ford Mustang).
• How To Test For A Blown Head Gasket (1990-1995 5.0L V8 Ford Mustang).
• How To Do And Interpret An Engine Compression Test (1990-1995 5.0L V8 Ford Mustang).