How To Test The Throttle Position Sensor (1997-2000 4.2L V6 Ford F150, F250)

TEST 2: Verifying Throttle Position Sensor Has Power

The TP sensor needs power (in the form of 5 Volts DC) to function. So, in this test section, we're gonna' make sure that it's getting power.

The brown with white stripe (BRN/WHT) wire labeled with the number 1 in the photo above is the one that feeds power to the TPS.

OK, let's get started:

1. 1

   Disconnect the TP sensor from its 3-wire connector.

2. 2

   Place your multimeter's dial in Volts DC mode.

3. 3

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

4. 4

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

5. 5

   Gently probe the female terminal of the connector that connects to the BRN/WHT wire with the red multimeter test lead.

6. 6

   Your multimeter should display 4.5 to 5 Volts on its screen.

Let's interpret your test result:

CASE 1: The TP sensor is being fed with 4.5 to 5 Volts. This means that the throttle position sensor (TPS) is getting power from your 4.2L Ford fuel injection computer.

The next and last test, is to make sure that the throttle position sensor is getting Ground (from the PCM too). For this test, go to: TEST 3: Verifying Throttle Position Sensor Has Ground.

CASE 2: The TP sensor IS NOT being fed with 4.5 to 5 Volts. Double check all of your connections and repeat the test.

If your multimeter still doesn't register the 4.5 to 5 Volts DC, then this test result tells you that the TPS itself is not at fault (and thus causing the TPS trouble code). Without power, your Ford's TPS can't create a throttle angle voltage signal. Although beyond the scope of this tutorial, your next step is to diagnose and restore this missing power.

TEST 3: Verifying Throttle Position Sensor Has Ground

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

1. You have a TPS trouble code (P0121, P0122, P0123).
2. The TPS is not creating the correct throttle plate angle voltage signal (TEST 1).
3. Th TPS is getting power in the form of 4.5 to 5 Volts DC (TEST 2).

The last test we need to do is to make sure that it's getting Ground.

The grey with red stripe (GRY/RED) wire, labeled with the number 3 in the photo above, is the one that supplies Ground.

IMPORTANT: Ground is provided directly by the fuel injection computer. Be careful and don't intentionally or accidentally short this wire (circuit) to battery power, or you will fry the fuel injection computer.

OK, here are the test steps:

1. 1

   Disconnect the TP sensor from its 3-wire connector.

2. 2

   Place your multimeter's dial in Volts DC mode.

3. 3

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

4. 4

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

5. 5

   Gently probe the female terminal of the connector that connects to the GRY/RED wire with the black multimeter test lead.

6. 6

   Your multimeter should display 4.5 to 5 Volts on its screen.

Let's interpret your test result:

CASE 1: The multimeter showed 10 to 12 Volts. This is the correct and expected test result and confirms the TPS is getting Ground.

You can conclude the TP sensor is bad and needs to be replaced if you have confirmed:

1. The TP sensor IS NOT producing a varying voltage signal when manually opening and closing the throttle plate (TEST 1).
2. The TP sensor is being fed 5 Volts DC (TEST 2).
3. The TP sensor is being fed Ground (TEST 3).

CASE 2: Multimeter DID NOT show 10 to 12 Volts. Double check that you're testing the correct TP sensor harness terminal wire and repeat the test.

If your test result still indicates that the TPS is not getting Ground, then we can conclude that one of two things are causing this lack of Ground:

1. There's an open in the wire between the TP sensor harness connector and the fuel injection computer's harness connector.
2. The fuel injection computer has an internal problem (although this is extremely rare).

Although testing these two conditions are beyond the scope of this article, you have now eliminated the throttle position sensor (TPS) on your 4.2L equipped Ford as being the cause of the problem and/or the TP sensor diagnostic trouble code (DTC) lighting up the check engine light (CEL).

More 4.2L Ford F150 And F250 Diagnostic Tutorials

You can find a complete list of 4.2L Ford F150 and F250 tutorials and wiring diagrams in this index:

• 4.2L Ford F150 And F250 Index of Articles.

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

• How To Test The Fuel Injectors (2001-2003 4.2L V6 Ford F150).
• How To Do An Engine Compression Test (1997-2003 4.2L V6 Ford F150, F250).
• How To Test The Ford EGR Valve EGR Vacuum Solenoid, DPFE Sensor.
• How To Test The Coil Pack (Ford 3.0L, 3.8L, 4.0L, 4.2L).