TEST 1: Testing The 5 Volt Reference Signal
The very first thing that you'll need to check is that 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
Place your multimeter in Volts DC mode.
- 2
Disconnect the TPS from its electrical connector.
- 3
Turn the key the ON position but don't start the engine.
- 4
Connect the red multimeter test lead (using the appropriate tool) to the wire labeled with the letter A.
- 5
Connect the black multimeter test lead to the negative (-) battery terminal.
- 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
Place your multimeter in Volts DC mode.
- 2
Disconnect the TPS from its electrical connector.
- 3
Turn the key the ON position but don't start the engine.
- 4
Connect the black multimeter test lead (using the appropriate tool) to the wire labeled with the letter B.
- 5
Connect the red multimeter test lead to the positive (+) battery terminal.
- 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.
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 TP Signal.
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).
