How to Test the Throttle Position Sensor (2.3L Ranger, Mustang, B2300)

In this tutorial, I'll help you troubleshoot the throttle position sensor (TPS) on your 2.3L Ford Ranger or 2.3L Ford Mustang.

You don't need a scan tool or any other expensive diagnostic tool to find out if it's BAD or not.

I'll explain the entire test in a step-by-step way. By the way, this throttle position sensor test is for:

  1. 1991, 1992, 1993 2.3L Ford Mustang.
  2. 1993, 1994 2.3L Ford Ranger.
  3. 1994 2.3L Mazda B2300.


Symptoms of a BAD Ford TPS

The very first thing you'll notice, when the TPS goes BAD on your 2.3L Ford Ranger or Mustang, is the check engine light shining nice and bright. You'll also see:

  1. TPS Diagnostic Trouble Codes (DTC's) stored in the vehicle's computer's memory.
    1. P0121: Throttle Position (TP) Circuit Performance Problem.
    2. P0122: Throttle Position (TP) Circuit Low Input.
    3. P0123: Throttle Position (TP) Circuit High Input.
  2. Really BAD gas mileage.
  3. Transmission does not shift out of second gear.
  4. No power as you accelerate the vehicle.
  5. Hesitation when you step on the Accelerator Pedal.

What Tools do
I Need for the TPS Test?

I can tell you right off the bat that the one thing you don't need is a Scan Tool. You need a few basic things and they are:

  1. Multimeter
    1. A digital or analog multimeter will work.
    2. If you need to buy one or are looking to upgrade, check out my recommendations here: Buying a Digital Multimeter for Automotive Diagnostic Testing.
  2. Wire Piercing Probe
    1. This tool is a time saver of the first order. To see what this tool looks like, click here: Wire Piercing Probe.

You'll need a helper to help you to perform the test steps in TEST 1. Other than that.. nothing else is needed.

Circuit Descriptions: Ford TPS

The throttle position sensor (TPS) on your 2.3L Ford Ranger (or 2.3L Ford Mustang or Mazda B2300) has 3 wires sticking out of its connector.

Each wire has a specific job to do and below you'll find out what each wire (circuit) does.

One very important thing to know is that all three circuits start and end at the PCM (Powertrain Control Module=Fuel Injection Computer) or vice-versa... depending on how you look at it.

  1. Circuit labeled 1:
    1. Power Circuit. 5 Volts from the PCM.
  2. Circuit labeled 2:
    1. Throttle Position (TP) Signal Circuit.
  3. Circuit labeled 3:
    1. Ground Circuit. Provided by the PCM internally.

NOTE: When checking for the signals the wire carry, you should not probe the front of the TP sensor's connector's terminals. I suggest you use a Wire-Piercing Probe (click here so that you can see what one looks like: Wire Piercing Probe) to connect to your multimeter.

Another important tip... since these three circuits go directly to the PCM, you need to be careful not to short these wires to Power (12 Volts) or you'll fry the PCM.

How Does the
Throttle Position Sensor (TPS) Work?

The throttle position sensor's job is to measure the angle of the throttle. So here, in a nutshell, is how the TPS on your Ford 2.3L Ranger or Mustang (Mazda B2300) works when you crank and start the engine:

  1. The Fuel Injection Computer supplies power and ground to the throttle position sensor.
    1. Power is in the form of 5 Volts.
    2. Both Power and Ground are provided by the PCM internally.
  2. When the throttle plate is closed (at idle) the TPS sends the PCM (Powertrain Control Module=Fuel Injection Computer) a DC voltage signal of about .9 to 1 Volt.
    1. This TP signal Voltage value is what the PCM associates with a Closed Throttle.
  3. When you step on the gas pedal and accelerate the Engine, the throttle plate opens.
    1. The throttle position sensor immediately measures the amount the throttle plate opens and sends this change of the throttle angle as an INCREASING voltage signal to the PCM.
  4. With this increasing voltage signal, the PCM knows its time to inject more fuel, advance ignition timing, and a host of other things it has to do to keep your Ford Ranger or Mustang (Mazda B2300) 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 TEST 1

Ford Vehicles:

  • Mustang 2.3L
    • 1991, 1992, 1993
  • Ranger 2.3L
    • 1989, 1990, 1991, 1992, 1993,1994, 1995, 1996, 1997, 1998

Mazda Vehicles:

  • B2300 2.3L
    • 1994, 1995