TEST 3: Testing The TP Signal

How To Test The Throttle Position Sensor (GM 3.1L, 3.4L)

Up until this point, your tests have verified that the throttle position sensor is getting 5 Volts and Ground. The next step is to see if it's producing a good signal that the PCM can use.

If the throttle position sensor (TPS) is working correctly, then as you open the throttle plate, the multimeter will register a smooth increase in the DC voltage until the maximum voltage is reached, which is about 4.5 Volts DC.

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

If the TPS is bad, its voltage signal will stay stuck in one value as you open/close the throttle plate. Or, the voltage signal will have sudden gaps as you open/close the throttle plate to its fully open or fully closed position, especially when you tap on the sensor.

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 (TPS) must remain connected to its electrical connector for this test to function properly. To be able to access the voltage inside the signal wire, you'll need to use either a back probe or a wire piercing probe. You can see an example of this tool here: Wire Piercing Probe.

OK, let's start testing:

  1. 1

    Place your multimeter in Volts DC mode.

  2. 2

    Connect the red test lead to the wire labeled with the letter C of the TP sensor harness connector.

  3. 3

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

  4. 4

    Manually rotate the throttle plate.

    You'll get the best results by opening and closing the throttle plate directly on the throttle body instead of stepping on the accelerator pedal.

  5. 5

    The multimeter should show an increasing voltage as you (or your helper) open up the throttle plate.

    You'll get the best results by opening and closing the throttle plate directly on the throttle body instead of stepping on the accelerator pedal.

  6. 6

    The multimeter should show a decreasing voltage as you begin to close the throttle plate.

  7. 7

    Using a screwdriver's handle, gently tap the TP sensor as you open and close the throttle plate and observe the multimeter.

    The purpose (of tapping the TP sensor with the screwdriver's handle) is to see if the TP sensor shows gaps in the voltage signal. Why? Because a good TP sensor will show a continuous increasing or decreasing voltage signal even while getting tapped by the screw-driver's handle.

Let's interpret your test result:

CASE 1: The multimeter registered a smooth increase or decrease in voltage. This is the correct test result and tells you 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, consult the suggestions found here: The TPS Code Won't Go Away.

CASE 2: The multimeter DID NOT register a smooth increase or decrease in voltage. Then the throttle position sensor (TPS) is bad only if you have confirmed that:

  1. The TPS sensor is not producing a voltage signal that increases/decreases as you open/close the throttle plate (TEST 1).
  2. The TPS sensor is receiving 5 Volts DC (TEST 2).
  3. The TPS sensor is receiving Ground (TEST 3).

If your TPS sensor tests produced the above 3 results, then replacing the throttle position sensor will solve the TPS diagnostic trouble code (DTC) lighting up your check engine light (CEL) on your GM car or mini-van.

CASE 3: The multimeter DID NOT register any voltage. Then the throttle position sensor (TPS) is bad only if you have confirmed that:

  1. The TPS sensor is not producing a voltage signal that increases/decreases as you open/close the throttle plate (TEST 1).
  2. The TPS sensor is receiving 5 Volts DC (TEST 2).
  3. The TPS sensor is receiving Ground (TEST 3).

If your TPS sensor tests produced the above 3 results, then replacing the throttle position sensor will solve the TPS diagnostic trouble code (DTC) lighting up your check engine light (CEL) on your GM car or mini-van.

The TPS Code Won't Go Away

So you've tested your GM car or mini-van's TPS and according to the test results, the TPS is good. But the check engine light keeps coming back on even after you erased the diagnostic trouble code (DTC) from the computer's (PCM) memory. 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.
    1. 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:
    1. I have found that the best way to test these intermittents 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.

Where To Buy The Throttle Position Sensor And Save

The following links will help you comparison shop for the original AC Delco (Delphi) throttle position sensor and after-market TPS:

Not sure if the above throttle position sensor fits your particular GM vehicle? Don't worry, once you get to the site they'll make sure it fits. If it doesn't, they find you the right part.

Related 3.1L, 3.4L Test Tutorials

If this tutorial was helpful, then the following tutorials will be too:

  1. Testing The Ignition Module And Crank Sensor (GM 3.1L, 3.4L).
  2. How To Test The Ignition Coil Packs (GM 3.1L, 3.4L).
  3. How To Test The GM MAF Sensor 3.1L, 3.4L, 4.3L, 5.0L and 5.7L.
  4. How To Clean The GM Mass Air Flow (MAF) Sensor.
  5. How To Troubleshoot A No Start (GM 3.1L, 3.4L) (at: troubleshootmyvehicle.com).
  6. How To Test The Fuel Pump No Start Tests (GM 3.1L, 3.4L) (at: troubleshootmyvehicle.com).
  7. How To Do A Fuel Injector Resistance Test (GM 3.1L, 3.4L) (at: troubleshootmyvehicle.com).
  8. How To Troubleshoot Misfire Codes (GM 3.1L, 3.4L) (at: troubleshootmyvehicle.com).
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Buick Vehicles:

  • Century 3.1L
    • 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005
  • Regal 3.1L
    • 1994, 1995, 1996
  • Rendezvous 3.4L
    • 2002, 2003, 2004, 2005
  • Skylark 3.1L
    • 1994, 1995, 1996, 1997, 1998

Chevrolet Vehicles:

  • Beretta 3.1L
    • 1994, 1995, 1996
  • Corsica 3.1L
    • 1994, 1995, 1996
  • Impala 3.4L
    • 2000, 2001, 2002, 2003, 2004, 2005
  • Lumina 3.1L
    • 1995, 1996, 1997, 1998, 1999, 2000, 2001

Chevrolet Vehicles:

  • Malibu 3.1L
    • 1997, 1998, 1999, 2000, 2001, 2002, 2003
  • Monte Carlo 3.1L, 3.4L
    • 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005
  • Venture 3.4L
    • 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005

Oldsmobile Vehicles:

  • Achieva 3.1L
    • 1994, 1995, 1996, 1997, 1998
  • Alero 3.4L
    • 1999, 2000, 2001, 2002, 2003, 2004
  • Cutlass (Ciera & Supreme) 3.1L, 3.4L
    • 1993, 1994, 1995, 1996, 1997

Oldsmobile Vehicles:

  • Silhouette 3.1L, 3.4L
    • 1994, 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004

Pontiac Vehicles:

  • Aztek 3.4L
    • 2001, 2002, 2003, 2004, 2005
  • Grand Am 3.1L, 3.4L
    • 1994, 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005

Pontiac Vehicles:

  • Grand Prix 3.1L
    • 1994, 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003
  • Montana 3.4L
    • 1999, 2000, 2001, 2002, 2003, 2004, 2005
  • Trans Sport 3.4L
    • 1996, 1997, 1998

Isuzu Vehicles:

  • Rodeo 3.2L
    • 1993, 1994, 1995
  • Trooper 3.2L
    • 1992, 1993, 1994, 1995