Testing The Throttle Position Sensor Circuits (1997-1999 Ford 4.6L, 5.4L)

TPS Power And Ground Circuits Shorted To Power Or Ground

If you've reached this point, you've done quite a bit of testing.

You have:

  1. Checked the continuity of the TPS signal circuit.
  2. Checked the continuity of the TPS power circuit.
  3. Checked the continuity of the TPS Ground circuit.
  4. Checked that the TPS signal circuit IS NOT shorted to power or Ground.

The one thing we haven't done, is to check/confirm that the TPS power and Ground circuits are not shorted to each other (or to power or Ground).

Why worry about the power (or ground) circuit being shorted to another circuit (wire)? Because this happens and is a possibility that needs to be checked to succesfully diagnose a trouble code that just won't go away.

What complicates checking the power and Ground circuit (of the TPS) is that they are shared by a few other sensors/components.

That's right, the TPS power circuit (BRN/WHT wire) and the TPS Ground circuit (GRY/RED wire) also provide power (5 Volts) and Ground to a few other sensors/components. One of these components could be internally fried (to battery power or chassis Ground) and causing the TPS code that won't go away.

To see what other components are tied to these two wires, take a look at the two illustrations of a simplified TPS wiring diagram you can see here: TP Sensor Wiring Diagram (1997-1999 Ford 4.6L, 5.4L).

So, if all of the tests you've done with the help of this tutorial have indicated:

  1. Continuity in all of the TPS circuits.
  2. The TPS is OK (because you either replaced it or have tested it).
  3. The PCM is still accusing the TPS as being bad.

Then your next steps should be to check that none of the other components, that share the TPS power and Ground circuits, ARE NOT fried. If they are fried, then there's a good possibility that this is causing the TPS problem that won't go away.

Once you've confirmed that the other components are OK, then it becomes possible to isolate the power and Ground circuits and check them for problems with shorts to power or Ground.

NOTE: If there's a problem with the power or Ground circuit, you're gonna' see quite a few diagnostic trouble codes (DTCs) lighting up the check engine light (CEL) on your Ford.

To be a bit more specific: All of the sensors/components tied to that shorted power circuit (or shorted Ground circuit) will have their trouble code stored in the PCM's memory. So, when you scan for trouble codes, your scan tool will display them all (the sensor's affected by the shorted circuit) giving you the impression that they are all bad.

More Ford 4.6L, 5.4L Diagnostic Tutorials

You can find a complete list of Ford 4.6L, 5.4L diagnostic tutorials in this index: Ford 4.6L, 5.4L Index Of Articles

Here's a small sample of the articles you'll find there:

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Ford Vehicles:
  • Crown Victoria 4.6L
    • 1997, 1998, 1999
  • Expedition 4.6L, 5.4L
    • 1997, 1998, 1999
  • E150 Van 4.6L
    • 1997, 1998, 1999
  • E150 Van 5.4L
    • 1997, 1998
  • E250 Van 4.6L
    • 1998, 1999
Ford Vehicles:
  • E250 Van 5.4L
    • 1997, 1998, 1999
  • E350 Van 5.4L
    • 1997, 1998, 1999
  • F150 Pickup 4.6L, 5.4L
    • 1997, 1998, 1999
  • F250 Pickup 4.6L, 5.4L
    • 1997, 1998, 1999
  • F350 Pickup 5.4L
    • 1999
Ford Vehicles:
  • Mustang 4.6L (SOHC and DOHC)
    • 1997, 1998, 1999
  • Thunderbird 4.6L
    • 1997