How To Test The TPS (1991, 1992, 1993, 1994, 1995 4.0L Ford Explorer And Aerostar)

You can easily and quickly test the throttle position sensor on your 1991-1995 4.0L Ford Explorer or Aerostar.

All you need is a multimeter. No scan tool is required. In this tutorial, I'll show you how to test it in a step-by-step manner.

With your test results, you'll be able to say that the TPS is good or bad.

You can find the 1991-1995 4.0L Ford Ranger (Mazda B4000) TPS test here:

APPLIES TO: This tutorial applies to the following vehicles:

  • 4.0L V6 Ford Aerostar: 1991, 1992, 1993, 1994, 1995.
  • 4.0L V6 Ford Explorer: 1991, 1992, 1993, 1994, 1995.

En Español You can find this tutorial in Spanish here: Cómo Probar El Sensor TPS (1991-95 Ford 4.0L Explorer, Ranger, Aerostar) (at: autotecnico-online.com).

Symptoms Of A Bad Throttle Position Sensor

As you're probably aware, the accelerator pedal connects to the throttle plate via a cable.

As you step on the accelerator pedal, the throttle plate opens. With the engine running, this results in more air entering the engine.

As you step off the accelerator pedal, the throttle plate closes, and less air enters the engine.

The fuel injection computer on your 4.0L Ford needs to know how much the throttle plate opens (as you step on or off the accelerator pedal) to calculate a host of things to keep the engine running smoothly and optimally.

Since the TP sensor is a critical sensor for the engine management system, engine performance suffers when it fails.

These are some of the symptoms that you're going to see when the TP sensor fails:

  • One of the following trouble codes lighting up the check engine light (CEL):
    • 23: Throttle Position Sensor Out of Self-Test Range.
    • 43: Throttle Position Sensor Below Idle Spec.
    • 53: Throttle Position Sensor Above Maximum Voltage.
    • 63: Throttle Position Sensor Below Minimum Voltage.
    • 121: Closed Throttle Position Sensor Voltage Higher or Lower Than Expected.
    • 122: Throttle Position Sensor Below Minimum Voltage.
    • 123: Throttle Position Sensor Above Maximum Voltage.
    • 124: Closed Throttle Position Sensor Voltage Higher Than Expected.
    • 125: Closed Throttle Position Sensor Voltage Lower Than Expected.
  • Hesitation when accelerating the engine.
  • Lack of power.
  • Bad gas mileage.

Where To Buy The TPS And Save

The following links will help you to comparison shop for the 1990-1994 4.0L Ford TPS. I think they'll save you a few bucks:

Not sure if the above TPS fits your particular 4.0L Ford Explorer (Aerostar)? Don't worry, once you get to the site they'll make sure it fits by asking you the specifics of your particular Ford vehicle. If it doesn't fit, they'll find you the right one.

TEST 1: Testing The TPS Voltage Signal

How To Test The TPS (1991, 1992, 1993, 1994, 1995 4.0L Ford Explorer And Aerostar)

As I mentioned earlier, the TPS produces a voltage signal that corresponds to the position of the throttle plate.

To give you more details, the TPS produces a small voltage signal when the throttle plate is closed.

As the throttle plate opens, the TPS produces a higher voltage signal. When the throttle plate reaches its maximum wide open position, the TPS produces a voltage of about 4.5 Volts DC.

Generally, when the TPS fails, its voltage signal will not increase/decrease as you open/close the throttle plate.

In this test section, you'll confirm the performance of the TPS voltage signal.

NOTE: You'll need a multimeter to be able to test the throttle position sensor. If you don't have one, check out my recommendations here: Buying A Digital Multimeter For Automotive Diagnostic Testing.

OK, let's start:

  1. 1

    Turn the key to the ON position but don't start the engine.

  2. 2

    Place your multimeter in Volts DC mode.

  3. 3

    Probe the wire labeled with the #2 (in the photo above) with the red multimeter test lead. This wire is usually a gray with white stripe (GRY/WHT) wire.

    Ground the black multimeter test lead on the battery negative (-) terminal.

    NOTE: The TP sensor must remain connected to its electrical connector. You'll need to use a back probe or a wiring piercing probe to tap into the signal of the middle wire. To see what a wire piercing probe looks like and where to buy one, go here: Wire Piercing Probe.

  4. 4

    Your multimeter should report a voltage between 0.2 to 0.9 Volts DC with the throttle plate closed. If your multimeter doesn't, don't worry about it just yet, continue with the other steps.

  5. 5

    Slowly open the throttle (by hand and from the engine compartment). The voltage numbers should increase as the throttle plate opens.

    This increase in voltage should be smooth and without any gaps or skips. Once the throttle is wide open, your multimeter should read somewhere between 3.5 to 4.5 Volts DC.

  6. 6

    Slowly close the throttle. As the throttle is closing, you should see the voltage decrease smoothly and without any gaps or skips, to the exact same voltage you noticed in step 3.

  7. 7

    Lightly tap on the throttle position sensor with the handle of a screw-driver (or something similar, and I want to emphasize the words ‘lightly tap’) as you slowly open and close the throttle and observe the multimeter.

    If the TPS is bad, the tapping will cause the voltage numbers to skip or go blank. If the TPS is OK, the tapping will have no effect on the voltage numbers.

  8. 8

    Repeat step 7 several times to make sure of your multimeter test results.

Let's take a look at your test results:

CASE 1: The TPS signal voltage increased/decreased as you opened/closed the throttle plate. This is the correct test result. It tells you that the throttle position sensor IS NOT defective.

This test result also confirms that the TPS is getting both power and Ground from the fuel injection computer.

CASE 2: The TPS signal voltage DID NOT increase/decrease as you opened/closed the throttle plate. This test result usually tells you that the TPS is bad.

So that you can make sure the TPS is bad, you need to make sure it's getting power and Ground. Go to: TEST 2: Making Sure The TPS Is Receiving 5 Volts.

CASE 3: The multimeter DID NOT register any voltage. This test result doesn't condemn the TP sensor as bad just yet.

Why? Because the TP sensor may be missing either power or Ground. So your next step is to check that the TP sensor is getting power and Ground. Go to: TEST 2: Making Sure The TPS Is Receiving 5 Volts.

Ford Vehicles:

  • Aerostar 4.0L
    • 1991, 1992, 1993, 1994, 1995
  • Explorer 4.0L
    • 1991, 1992, 1993, 1994, 1995