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 pickup, 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:

• TPS diagnostic trouble codes (DTCs) stored in the vehicle's computer's memory.
  • P0121: Throttle Position (TP) Circuit Performance Problem.
  • P0122: Throttle Position (TP) Circuit Low Input.
  • P0123: Throttle Position (TP) Circuit High Input.
• Really bad gas mileage.
• Transmission does not shift out of second gear.
• No power as you accelerate the vehicle.
• 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

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.

• Circuit labeled 1:
  • Power Circuit. 5 Volts from the PCM.
• Circuit labeled 2:
  • Throttle Position (TP) Signal Circuit.
• Circuit labeled 3:
  • 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 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 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 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.

Where To Buy The TPS And Save

I think that the best place to save some buck on the TPS is online. Check out the following links and compare:

TEST 1: Testing The TP Signal

We're gonna start off by checking that the TPS is producing a viable throttle angle signal to the PCM.

If the throttle position sensor (TPS) is good, the multimeter will register a smooth and linear increase in the DC voltage till it reaches the a maximum voltage of about 4.5 to 4.9L Volts DC, without any gaps in the signal.

Then, as you slowly release the throttle back to its closed position, the multimeter will display a gradual and linear decrease in voltage till the initial base voltage is reached (which you recorded in the beginning of the test).

If the TPS is bad, the voltage signal will stay stuck in one value or there will be sudden gaps in the voltage reading as you open/close the throttle plate, especially when you tap on the sensor.

NOTE:You'll need a helper to assist you in this test step, since he or she will need to lightly tap on the throttle position sensor's body with a screw driver (or other appropriate tool) while you observe the multimeter and manually actuate the throttle.

IMPORTANT: The throttle position sensor must remain connected to its electrical connector for this test to function. You'll need to use a back probe or a wire piercing probe to access the signal within the wire. You can see an example of this tool here: Wire Piercing Probe.

OK, let's start testing:

PART 1

1. 1

   Select Volts DC mode on your multimeter.

2. 2

   Probe the circuit labeled with the number 2 in the photo with the red multimeter test lead, using an appropriate tool to pierce the wire.

3. 3

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

4. 4

   Turn the Key On with the engine Off.
   
   Your multimeter should register about 0.9 to 1 Volt (this voltage specification might vary a little bit on your vehicle).

PART 2

1. 5

   Manually rotate the throttle plate by hand as you eye-ball the multimeter's voltage readings.

2. 6

   The multimeter's initial voltage reading should increase smoothly as you open the throttle plate to its Wide Open Position. At Wide Open Throttle, the reading on your multimeter should read about 4.5 to 4.9 Volts DC.

3. 7

   Now, slowly release the throttle plate to its fully closed position, all the while observing the multimeter's reading.

4. 8

   The multimeter's voltage reading should decrease in a smooth and linear fashion back to the exact same voltage you noticed in step 5.

PART 3

1. 9

   OK, now have your helper lightly tap the TP sensor with the butt of a screw-driver's handle (or something similar).

2. 10

   As your helper taps, slowly and smoothly open the throttle to its open-wide position. The readings on your multimeter should increase and max out at about 4.5 to 4.9 Volts DC, at Wide Open Throttle.

3. 11

   Now, slowly release the throttle back to its closed position. Your multimeter should read the base voltage that you recorded in step 5 of this test.

4. 12

   All the while you've got your eyes glued on the multimeter to see if the tapping affects the voltage readings.

5. 13

   Repeat this (tapping the throttle position sensor) several times to make sure of your results.

Let's interpret your test results:

CASE 1: The multimeter registered a smooth increase or decrease in voltage. This is the correct test result.

You can conclude that the TP sensor is working OK and is not the cause of the TPS fault code issue. If the fuel injection computer is still setting a TPS trouble code, go to: TPS Code Won't 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. Your next test is to make sure that the TPS is getting power. Go to: TEST 2: Testing The 5 Volt Reference Signal.