How To Test The 3.0L Ford Throttle Position Sensor (TPS)

Troubleshooting and testing the throttle position sensor on your Ford or Mercury with a 3.0L V6 engine can easily be done in three tests and without a scan tool. That's right, no Scan Tool needed for these tests. This article will show how with step by step instructions. You'll be able to diagnose the TPS as BAD or not.

In case you're wondering if this article applies to your particular Ford or Mercury or Mazda car or pick up, you can take a look at the application list at the bottom of this page.

Symptoms Of A BAD Ford TPS

You'll have the CHECK ENGINE LIGHT on, for sure, on your Ford or Mercury's Instrument Cluster and one of several of the following symptoms:

  1. TPS diagnostic trouble codes (DTCs) 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?

You'll need a multimeter for the TPS diagnostic test on your Ford (Mercury) vehicle (don't have a digital multimeter? Need to buy one? Click here to see my recommendations: Buying A Digital Multimeter For Automotive Diagnostic Testing) and a helper to help you to perform the test steps in TEST 3. Other than that.. nothing else is needed.

Circuit Descriptions: Ford TPS

How To Test The 3.0L Ford Throttle Position Sensor (TPS)

The Ford (or Mercury) throttle position sensor is a simple three wire TPS. Below you'll find out what each wire (circuit) does. 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.

One very important testing tip I'm going to share with you that may save you a big headache is that you should not probe the front of the TP sensor's connector's terminals to test for the 5 Volts and Ground Signals. I suggest you use a Wire-Piercing Probe (click here so that you can see what one looks like: Wire Piercing Probe) to get to and verify the presence of these two Signals.

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 Ford (Mercury) 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 or Mercury or Mazda car (pick up, mini-van) works when you crank and start it:

  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 .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 its time to inject more fuel, advance ignition timing, and a host of other things it has to do to keep your Ford Explorer (Mercury Mountaineer) 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.