TEST 1: Testing The 5 Volt Reference Signal
The engine on your GM car or truck must be fully warm (normal operating temperature) to successfully diagnose the throttle position sensor. So, if it's not warmed up already, go ahead and crank her up and get her warmed up.
The first test is 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). Here are the test steps:
Once you have warmed up the engine, turn it off and remove any thing that may be hiding or impeding access to the TP sensor's connector.
With the red multimeter test lead, and an appropriate tool, probe the circuit labeled with the number 3 in the photo.
Connect the black multimeter test lead to a good and clean ground point on the engine or directly on the negative battery terminal.
Turn the Key to its ON position but do not start the engine. Your multimeter should read 4.5 to 5 Volts.
Let's take a look at what your test results mean:
CASE 1: If 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 2: Testing The Sensor Return (Ground) Circuit.
CASE 2: If 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 2: Testing The Sensor Return (Ground) Circuit
Now that you have verified that the TPS on your GM car or pick up is getting power, you need to check that it's also getting a good Ground.
The PCM is the one that completes the path to ground for the TPS internally. Therefore, be careful. Do not accidentally or intentionally short this wire to power or you're gonna' have a fried PCM on your hands.
With your multimeter still in Volts DC mode from TEST 1.
Probe the circuit labeled with the number 2 in the photo, with the black multimeter test lead.
The red multimeter test lead goes to the battery positive terminal.
Turn the Key to its ON position but don't start the engine.
The multimeter should display 11 to 12 Volts.
Let's take a look at your test results:
CASE 1: If the multimeter displayed 11 to 12 Volts. This test result tells you that the PCM is feeding a good Ground to the TP sensor. The next step is to verify that the TP sensor is creating a good throttle position signal the PCM can use, go to: TEST 3: Testing The Throttle Position Sensor Signal.
CASE 2: If the multimeter DID NOT display 11 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).