How To Test The Throttle Position Sensor (Ford 5.0L, 5.8L)

TEST 2: Making Sure The TPS Is Getting 5 Volts

You've reached this test step after performing TEST 1 and getting a signal voltage that does not increase/decrease as you open/close the throttle plate.

In this test step, you'll check that the throttle position sensor is getting power.

Power is in the form of 5 Volts and these 5 Volts DC are fed to the TPS by your Ford's fuel injection computer.

This is what you'll need to do:

1. 1

   Place your multimeter in Volts DC mode.

2. 2

   Disconnect the TPS from its electrical connector.

3. 3

   Turn the key the ON position but don't start the engine.

4. 4

   Connect the red multimeter test lead (using the appropriate tool) to the wire labeled with the number 1.

5. 5

   Connect the black multimeter test lead to the negative (-) battery terminal.

6. 6

   Your multimeter should read 4.5 to 5 Volts DC.

Let's interpret your test result:

CASE 1: The multimeter registered 4.5 to 5 Volts. This is the correct test result and this confirms that the PCM is providing the correct voltage to the TPS.

The next step is to check that the TPS is getting Ground. For this test go to: TEST 3: Making Sure The TPS Is Getting Ground.

CASE 2: The multimeter DID NOT register 4.5 to 5 Volts. Without these 5 Volts the throttle position sensor will not function.

This missing voltage could be the result of an open-circuit problem in the circuit (wire) or the ECM may be fried (although this is rare).

Altho' testing these two conditions are beyond the scope of this tutorial, 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).

TEST 3: Making Sure The TPS Is Getting Ground

So far, you've done TEST 1 and TEST 2 and you have confirmed that:

• The throttle position sensor signal does not increase/decrease as you open/close the throttle plate.
• The throttle position sensor is getting 4.5 to 5 Volts DC.

In this test step, you're gonna' verify that the PCM is or is not providing a Ground to the throttle position sensor.

NOTE: Ground is provided by your Ford's fuel injection computer. So be careful and do not apply battery power (12 Volts DC) to the Ground wire or you'll fry the computer. The voltage test I'm describing below (to test for Ground) is a safe way of verifying the presence of this Ground.

OK, let's start:

1. 1

   Place your multimeter in Volts DC mode.

2. 2

   Disconnect the TPS from its electrical connector.

3. 3

   Turn the key the ON position but don't start the engine.

4. 4

   Connect the black multimeter test lead (using the appropriate tool) to the wire labeled with the number 3.

5. 5

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

6. 6

   Your multimeter should read 10 to 12 Volts DC.

Let's analyze your test result:

CASE 1: The multimeter displayed 10 to 12 Volts. This is the correct test result and it confirms that the PCM is feeding a good Ground to the TP sensor.

This also means that the TPS is bad and needs to be replaced only if you have:

• The throttle position sensor's voltage signal does not increase/decrease as you open/close the throttle plate (TEST 1).
• The throttle position sensor is getting 4.5 to 5 Volts DC (TEST 2).
• The throttle position sensor is getting Ground (confirmed in this test section).

CASE 2: The multimeter DID NOT display 10 to 12 Volts. This test results tells you that the TPS is not getting Ground and without it, it won't function.

The most likely cause of this missing Ground is an 'open-circuit' problem in this wire (between the TPS and the PCM).

Altho' testing these two conditions are beyond the scope of this tutorial, 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).

The TPS Code Won't Go Away

Every now and then, you'll get a TPS diagnostic trouble code that won't go away and keeps lighting up the check engine light. Either you've already replaced it or you've tested it (and it passed with flying colors).

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.

More Ford 5.0L And 5.8L Tutorials

You can find a complete list of 'how to test' tutorials for the 4.9L, 5.0L, and 5.8L Ford equipped vehicles here: Ford 4.9L, 5.0L, 5.8L Index Of Articles.

Here's a sample of the tutorials you'll find in the index:

• How To Test The MAP Sensor (at: troubleshootmyvehicle.com).
• How To Test For A Blown Head Gasket (at: troubleshootmyvehicle.com).
• How To Test The Fender Mounted Ignition Control Module.
• How To Test The Distributor Mounted Ignition Control Module.
• How To Test The Mass Air Flow Sensor.