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

TEST 2: Testing The 5 Volt Reference Signal

The second test that you'll need to do is to make sure the throttle position sensor is receiving power, which in this case is 5 Volts.

I recommend that you perform all of these tests with the engine (and therefore the TPS) at normal engine operating temperature, this is important. Now, in case you've been wondering, all of the TPS tests on your GM vehicle are done with the engine OFF.

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

   With the red multimeter test lead gently probe the female terminal that connects to the wire labeled with the letter A (see photo above).

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 analyze your test results:

CASE 1: The multimeter registered 4.5 to 5 Volts. This test result confirms that the fuel injection computer and the circuit is supplying the TPS with power. The next step is to test the Signal Return Circuit, go to: TEST 2: Testing The Sensor Return (Ground) Circuit.

CASE 2: The multimeter DID NOT register 4.5 to 5 Volts. Then the computer or the circuit are NOT providing the voltage that the TPS needs to operate. The two most likely reasons for this are: 1) an open-circuit problem in the circuit or 2) the PCM may be fried. Altho' it's beyond the scope of this article to test these two conditions, you have now eliminated the throttle position sensor (TPS) on your vehicle as being the cause of the problem and/or the TPS diagnostic trouble code (DTC) lighting up the check engine light (CEL).

TEST 2: Testing The Sensor Return (Ground) Circuit

Besides providing the TPS with power (5 Volts), the PCM also has to provide a Ground for the throttle position sensor, and in this test step you're gonna' check that it is.

NOTE: Since Ground is provided by your vehicle's fuel injection computer, 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 Ground in the wire.

Alright, 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

   With the black multimeter test lead gently probe the female terminal that connects to the wire labeled with the letter B (see photo above).

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 interpret your test result:

CASE 1: The multimeter displayed 10 to 12 Volts. This the correct test result and confirms that the PCM and the wire/circuit (that supply this Ground) are OK.

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

• Confirmed that the TPS voltage signal does not increase/decrease as you open/close the throttle plate (TEST 1).
• Confirmed that the TP sensor is getting 5 Volts (TEST 2).
• Confirmed, in this test section, that the TP sensor is getting Ground from the computer.

CASE 2: The multimeter DID NOT display 10 to 12 Volts. Without Ground the TPS won't function. This usually indicates a problem with either the PCM (internal fault/problem) or an open in the wire between the TPS and the PCM itself.

Altho' testing these two conditions are beyond the scope of this article, you have now eliminated the throttle position sensor (TPS) on your GM 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

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.
   • 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.

Related 3.1L, 3.4L Test Tutorials

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

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