TPS TEST 2: Testing The 5 Volt Reference Signal

How To Test The GM 3.8L Throttle Position Sensor (TPS)

The throttle position sensor (TPS) on your 3.8L V6 Buick (or Chevy, Olds, Pontiac) needs power to work. This power comes in the form of 5 Volts DC from the fuel injection computer.

This test will help you to confirm if these 5 Volts are present or not. This is what you'll need to do:

  1. 1

    Grab your multimeter and select Volts DC mode on it. You're gonna' test the Gray wire, this is the one that supplies power to the TPS. This is the wire that connects to the terminal labeled with the letter C (in the illustration above).

  2. 2

    Probe the Gray wire, with the RED multimeter lead and an appropriate tool (like a Wire-Piercing Probe). The throttle position sensor's connector can be connected to the sensor or not when you probe this circuit.

    It's important that you do not probe the front of the connector or you run the risk of damaging the terminal.

  3. 3

    Connect the BLACK multimeter lead to a good and clean ground point on the engine or directly on the negative battery terminal.

  4. 4

    When everything is set up, have a helper rotate the Key to its ON position but don't start the engine.

  5. 5

    The multimeter should display 4.5 to 5 Volts on its screen. OK, now let's interpret your test results below:

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

CASE 1: If the multimeter registered 4.5 to 5 Volts, this confirms that the Fuel Injection Computer and the circuit is supplying the TPS with power.

The next step is to test the ground circuit of the throttle position sensor, go to TEST 3.

CASE 2: If 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 short 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 3.8L V6 Buick (or Chevy, Olds, Pontiac) as being the cause of the problem and/or the TPS Diagnostic Trouble Code (DTC) lighting up the check engine light (CEL).

TPS TEST 3: Ground Circuit Test

How To Test The GM 3.8L Throttle Position Sensor (TPS)

So far you have verified that the TPS is not creating a throttle position signal (TPS TEST 1) and that the TPS is getting power (TPS TEST 2). The second step, before condemning the throttle position sensor, is to verify that it also has a good ground. The PCM is the one that provides this ground internally... so be careful and don't accidentally or intentionally apply power (12 Volts) to this circuit or you'll fry the PCM. OK, here are the test steps:

  1. 1

    With your multimeter still in Volts DC mode from TPS TEST 2.

  2. 2

    Probe the Black wire, with the BLACK multimeter lead. The TPS connector can be connected or not to the sensor. This is the wire that connects to the terminal labeled with the letter A (in the illustration above).

    It's important that you do not probe the front of the connector or you run the risk of damaging the terminal.

  3. 3

    Now, with the RED multimeter lead, probe the battery positive terminal.

  4. 4

    Once again, when everything is ready, have your helper turn the Key to its ON position but don't start the engine.

  5. 5

    If this circuit is OK and the PCM is providing a good path to ground, your multimeter will display 11 to 12 Volts.

Let's take a look at your test results:

CASE 1: If the multimeter showed 11 to 12 Volts, then the PCM and the wire/circuit (that supply this ground) are OK.

This multimeter test result also confirms that the TPS sensor is BAD and needs to be replaced, since you have verified that the TPS is not producing a signal and does have power and ground.

CASE 2: If the multimeter DID NOT show 11 to 12 Volts, then this 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 3.8L V6 Buick (or Chevy, Olds, Pontiac) as being the cause of the problem and/or the TPS Diagnostic Trouble Code (DTC) lighting up the check engine light (CEL).