How To Test The TPS (1995, 1996, 1997, 1998, 1999, 2000 4.0L V6 Ford Ranger And Mazda B4000)

You can easily and quickly test the throttle position sensor (TPS) on your 1995-2000 4.0L OHV Ford Ranger (Mazda B4000) with a multimeter.

In this tutorial, I'll show you how in a step-by-step manner. You'll quickly determine if the TPS is good or bad.

NOTE: You can find the 1995-2000 4.0L OHV Ford Explorer (Aerostar and Mercury Mountaineer) TPS test here:

APPLIES TO: This tutorial applies to the following vehicles:

  • 4.0L V6 OHV Ford Ranger: 1995, 1996, 1997, 1998, 1999, 2000.
  • 4.0L V6 OHV Mazda B4000: 1995, 1996, 1997, 1998, 1999, 2000.

OHV: Over Head Valve.

NOTE: If you need to test the older style TPS (1995 and older), see this tutorial: How To Test The TPS (1991-1995 4.0L Ford Explorer).

Symptoms Of A Bad TPS

The first thing you'll notice, when the TPS fails, is the check engine light shining nice and bright with one of the following diagnostic trouble codes:

  • P0121: Throttle Position Circuit Performance Problem.
  • P0122: Throttle Position Circuit Low Input.
  • P0123: Throttle Position Circuit High Input.
  • P1120: Throttle Position Sensor Out Of Range.
  • P1121: Throttle Position Sensor Inconsistent With MAF Sensor.
  • P1124: Throttle Position Sensor Out Of Self-Test Range.
  • P1125: Throttle Position Sensor Intermittent.

Besides a TPS diagnostic trouble code, you'll see one or more of the following symptoms:

  • Bad gas mileage.
  • Transmission does not shift out of second gear. Now, this doesn't happen very often, but it happens.
  • No power and/or hesitation as you accelerate the vehicle.

How The Throttle Position Sensor Works

In a nutshell, the throttle position sensor's job is to measure the angle of the throttle plate as you step on or off the accelerator pedal. Here are some more specifics:

  1. The fuel injection computer supplies 5 Volts and Ground to the throttle position sensor.
  2. Now, since the throttle is closed, the TPS (with power and Ground supplied) sends the PCM (Powertrain Control Module=Fuel Injection Computer) a DC voltage signal of about 0.9 to 1 Volt. This value is what the PCM associates with a closed throttle.
  3. Once you throw the car in drive and accelerate the car, the throttle opens and the throttle position sensor immediately sends this change of the Throttle angle as an INCREASING voltage signal to the PCM.
  4. With this increasing voltage signal, the PCM knows it's time to inject more fuel, advance ignition timing, and a host of other things it has to do to keep your Ford Ranger (Mazda B4000) running optimally.
  5. As you let go off the accelerator pedal to slow down, the throttle plate closes and of course the TP sensor sends the info to the PCM as it returns to its base voltage signal, till the whole cycle begins again.

Pretty easy stuff? The cool thing is that the tests to check out the TP sensor's performance are as easy too. Now, since you'll be working in the engine compartment take all necessary safety precautions and use common sense. OK, enough of my yakking, let's get this show on the road, go to: TPS TEST 1: Testing The TPS Signal.

Where To Buy The TPS And Save

The following links will help you to comparison shop for the 1995-2000 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 Ranger (Mazda B4000)? 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.

TPS TEST 1: Testing The TPS Signal

Testing The TPS Signal. How To Test The TPS (1995, 1996, 1997, 1998, 1999, 2000 4.0L V6 Ford Ranger And Mazda B4000)

When the throttle position sensor fails, it'll stop producing a voltage signal that corresponds to the throttle plate angle.

In plain English this means that the TPS will stop creating a voltage signal or the voltage signal will not increase/decrease as you open/close the throttle plate.

To confirm this issue, you'll connect a multimeter to the TPS signal wire and then manually open/close the throttle plate. You should see the TPS voltage signal increase/decrease as you open/close the throttle plate.

If you don't have a multimeter and need to buy one, check out my recommendations here: Buying A Digital Multimeter For Automotive Diagnostic Testing.

OK, let's start testing:

  1. 1

    Place your multimeter in Volts DC mode.

  2. 2

    Connect the red multimeter test lead to the gray with white stripe (GRY/WHT) wire of the TP sensor harness connector.

    The GRY/WHT wire connects to the female terminal identified with the number 2 in the photo above.

    NOTE: The TPS must remain connected to its connector to test the TPS voltage signal.

  3. 3

    Connect the black multimeter test lead directly on the battery negative (-) post.

  4. 4

    Turn the key on but don't crank or start the engine.

  5. 5

    Manually rotate the throttle plate.

    You'll get the best results by opening and closing the throttle plate directly on the throttle body instead of stepping on the accelerator pedal.

  6. 6

    The multimeter should show an increasing voltage as you (or your helper) open up the throttle plate.

  7. 7

    The multimeter should show a decreasing voltage as you begin to close the throttle plate.

  8. 8

    Using a screwdriver's handle, gently tap the TP sensor as you open and close the throttle plate and observe the multimeter.

    The purpose (of tapping the TP sensor with the screwdriver's handle) is to see if the TP sensor shows gaps in the voltage signal. Why? Because a good TP sensor will show a continuous increasing or decreasing voltage signal even while getting tapped by the screw-driver's handle.

Let's take a look at what your test results mean:

CASE 1: The voltage increased/decreased as you opened/closed the throttle plate. This is the correct test result and it indicates the throttle position sensor is OK.

With this test result you can also conclude that the TPS is receiving power and Ground. No further testing is necessary.

Now, if the throttle position sensor code keeps coming back, take a look at the heading: TPS Code Will Not Go Away for a few more suggestions as to what could be causing the TPS diagnostic trouble code (DTC).

CASE 2: The multimeter DID NOT register a smooth increase or decrease in voltage. This usually tells you that the throttle position sensor (TPS) is bad.

To confirm that the TPS is bad, the next steps are to make sure that the throttle position sensor is getting power and Ground. Go to: TPS TEST 2: Making Sure The TPS Is Receiving 5 Volts.

CASE 3: The multimeter DID NOT register any voltage. This usually tells you that the throttle position sensor (TPS) is bad.

To confirm that the TPS is bad, the next steps are to make sure that the throttle position sensor is getting power and Ground. Go to: TPS TEST 2: Making Sure The TPS Is Receiving 5 Volts.

Ford Vehicles:

  • Ranger 4.0L
    • 1995, 1996, 1997, 1998, 1999, 2000

Mazda Vehicles:

  • B4000 4.0L
    • 1995, 1996, 1997, 1998, 1999, 2000