How To Test The 4.6L, 5.4L Ford Throttle Position Sensor (TPS)

TPS TEST 2: Testing The 5 Volt Reference Signal

The second test we'll do, is to make sure that the throttle position sensor (TPS) is getting power.

As you already know, this power is in the form of 5 Volts DC and is provided by the PCM.

This test (as all of the tests in this article) must be done with a multimeter, either digital or analog. Also, I recommend that the engine be at its operating temperature since the heat accumulated by the TPS from the engine may help to find a stubborn glitch in the sensor.

Don't have a digital multimeter? Need to buy one? Click here to see my recommendations: Buying A Digital Multimeter For Automotive Diagnostic Testing.

These are the steps:

1. 1

   Put your multimeter in Volts DC mode.

2. 2

   With the red multimeter test lead, and an appropriate tool, probe the circuit labeled with the number 1 (see photo above).

3. 3

   Connect the black multimeter test lead to a good and clean Ground point on the engine or directly on the negative battery terminal.

4. 4

   Turn the key to its ON position but do not start the engine.

5. 5

   Your multimeter should read 4.5 to 5 Volts.

Let's analyze your test results:

CASE 1: The multimeter registered 4.5 to 5 Volts. This is the correct test result.

The next step is to make sure that the TPS is getting Ground. For this test go to: TPS TEST 3: Testing The Sensor Return (Ground) Circuit.

CASE 2: The multimeter DID NOT register 4.5 to 5 Volts. Then the PCM is NOT feeding the appropriate voltage either because there's an open-circuit problem in the circuit or the PCM is fried (not very common).

Altho' testing these two conditions are beyond the scope of this article, you have now eliminated the throttle position sensor (TPS) on your Ford vehicle as being the cause of the problem and/or the TPS diagnostic trouble code (DTC) lighting up the check engine light (CEL).

TPS TEST 3: Testing The Sensor Return (Ground) Circuit

If you've reached this point, then you've confirmed that:

• The TPS is not producing a voltage signal that increases/decreases as you open/close the throttle plate (TEST 1).
• The TPS is getting power (5 Volts DC) from the PCM (TEST 2).

The next test is to confirm that the PCM is feeding the TPS with Ground.

We'll do a simple multimeter voltage test to check for the presence of Ground in the circuit.

NOTE: Ground is provided by the PCM, so be careful not to connect this wire to battery power (12 Volts) either intentionally (or accidentally) or you'll fry the PCM. The multimeter voltage test I'm suggesting in the test instructions is a safe way to test for the presence of Ground in this circuit.

OK, let's start:

1. 1

   Put your multimeter in Volts DC mode.

2. 2

   With the black multimeter test lead, and an appropriate tool, probe the circuit labeled with the number 3 in the photo above.

3. 3

   Connect the red multimeter test lead directly on the battery positive (+) terminal.

4. 4

   Turn the key to its ON position but do not start the engine.

5. 5

   Your multimeter should read battery voltage (10 to 12 Volts).

Let's interpret your test results:

CASE 1: The multimeter registered 10 to 12 Volts. This test result lets you know the PCM is feeding a good Ground to the TP sensor.

You can conclude that the TPS is bad and needs to be replaced if you have:

• Confirmed the TPS is not producing a voltage signal that increases/decreases as you open/close the throttle plate (TEST 1).
• Confirmed the TPS is getting 5 Volts DC from the PCM (TEST 2).
• Confirmed the TPS is getting Ground from the PCM (this test section).

CASE 2: The multimeter DID NOT register 10 to 12 Volts. This test result lets you know that the TPS is not getting Ground, either because there's an open-circuit problem in the circuit or the PCM is fried (not very common).

Altho' testing these two conditions are beyond the scope of this article, you have now eliminated the throttle position sensor (TPS) on your Ford vehicle as being the cause of the problem and/or the TPS diagnostic trouble code (DTC) lighting up the check engine light (CEL).

TPS Code Won't Go Away

So you've tested the TPS per the instructions in this article and according to the test results, the TPS is good, yet the check engine light is still on. Well, here are a couple of suggestions that might inspire your next diagnostic move:

1. The throttle plate's idle-stop screw's factory adjustment has been altered so that the engine could be idled up and mask a miss/misfire and/or rough idle. This increases the TP sensor's signal to the PCM. The PCM doesn't like it and lights up the check engine light (CEL).
2. The throttle cable is binding and causing the throttle plate to not fully close.
   • This can be verified by simply having someone inside the vehicle pushing the accelerator pedal to the floor and releasing it, with the engine OFF, while you visually check that the throttle plate and cable are not getting stuck somewhere in their travel.
3. The TPS is failing intermittently. Which means that it works fine most of the time, but every now and then it doesn't:
   • I have found that the best way to test these intermittent problems is to road-test the vehicle with the multimeter hooked up to the TP Signal Wire with a long wire so that I can comfortably observe the signal going up and down as I or someone else drives.
4. The TP sensor's connector is bad, usually the locking tab is broken and the connector has worked itself loose, causing an intermittent false connection.