How To Test The Throttle Position Sensor (GM 4.3L, 5.0L, 5.7L)

TEST 2: Testing The 5 Volt Reference Signal

For our second test, we need to verify that the throttle position sensor (TPS) is getting power, which in this case is 5 Volts.

This voltage comes from the PCM (Powertrain Control Module=Fuel Injection Computer) and is delivered by the wire labeled with the number 3 (see photo above).

We'll do a simple multimeter voltage test to check for the presence of 5 Volts in this wire.

Here are the test steps:

1. 1

   Disconnect the throttle position sensor from its electrical connector.

2. 2

   Place your multimeter in Volts DC mode.

3. 3

   With the red multimeter test lead, and an appropriate tool, probe the circuit labeled with the number 3 in the photo.
   
   NOTE: If you probe the front of the female terminal (that connects to the wire), be careful and don't damage it with the multimeter's test probe.

4. 4

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

5. 5

   Turn the key to its ON position but do not start the engine.

6. 6

   Your multimeter should read 4.5 to 5 Volts.

Let's take a look at what your test results mean:

CASE 1: The multimeter registered 4.5 to 5 Volts. So far so good since this confirms that the PCM on your GM vehicle is providing power to the TPS.

The next step is to test the Ground circuit, go to: TEST 3: Testing The Sensor Return (Ground) Circuit.

CASE 2: The multimeter DID NOT register 4.5 to 5 Volts. Then the fuel injection computer is NOT providing the voltage that the TPS needs to operate.

This missing voltage could be the result of an open-circuit problem in the circuit or the PCM may be fried. 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).

TEST 3: Testing The Sensor Return (Ground) Circuit

Up to this point, you have confirmed that:

• The TPS voltage signal is stuck in one value (TEST 1).
• The TPS is getting power (TEST 2).

For our final test, we need to check that the throttle position sensor is also getting Ground.

IMPORTANT: The PCM is the one that completes the path to Ground for the TPS internally. Be careful not accidentally or intentionally connect this wire to battery 12 Volts or you're gonna' have a fried PCM on your hands. The multimeter voltage test I'm suggesting in the instructions below is a safe way to test for the presence of Ground in this wire.

Let's get started:

1. 1

   Disconnect the throttle position sensor from its electrical connector.

2. 2

   Place your multimeter in Volts DC mode.

3. 3

   With the black multimeter test lead, and an appropriate tool, probe the circuit labeled with the number 2 in the photo.
   
   NOTE: If you probe the front of the female terminal (that connects to the wire), be careful and don't damage it with the multimeter's test probe.

4. 4

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

5. 5

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

6. 6

   The multimeter should display 10 to 12 Volts.

Let's take a look at your test results:

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

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

• Confirmed the TPS voltage signal is stuck in one value (TEST 1).
• Confirmed the TPS is getting power (TEST 2).
• Confirmed in this test section that the TPS is getting Ground.

CASE 2: The multimeter DID NOT display 10 to 12 Volts. Then the PCM is NOT supplying a Ground either because of an internal fault/problem or there's 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).

TPS Code Won't Go Away

So you've tested the TPS per the instructions in this tutorial and according to the test results, the TPS is good, yet the check engine light is still on. 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 cable 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.