TEST 2: Verifying Throttle Position Sensor Has Power

How To Test The Throttle Position Sensor (1986, 1987, 1988, 1989, 1990, 1991 S10/S15)

In this test section we're going to check that the TPS is getting power power.

This power is in the form of 5 Volts DC and are provided by the gray GRY wire of the TPS connector.

The GRY wire is the one that connects to the TPS pin labeled with the letter C in the illustration above.

OK, let's get testing:

  1. 1

    Set your multimeter to Volts DC mode.

  2. 2

    Check the GRY wire of the TPS connector with the red multimeter test lead.

    IMPORTANT Be careful when probing the metal terminal of the TPS connector. Damaging the terminal will require that you replace the connector. Use a back probe or a wire piercing probe instead of probing the front of the connector.

  3. 3

    Connect the black multimeter test lead to a good and clean Ground point on the engine or directly on the negative (-) battery terminal.

  4. 4

    When you've set up the test, have a helper turn the key on but don't crank or start the engine.

  5. 5

    Your 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: The GRY wire, of the TPS connector, has 4.5 to 5 Volts. So far so good since this tells you that the throttle position sensor (TPS) is getting power from the fuel injection computer.

The next and last test, is to make sure that the throttle position sensor is getting Ground (from the PCM too). For this test, go to: TEST 3: Verifying Throttle Position Sensor Has Ground.

CASE 2: The GRY wire, of the TPS connector, DOES NOT have 4.5 to 5 Volts. Double check all of your connections and repeat the test. If your multimeter still doesn't register the 4.5 to 5 Volts DC...

, then this test result tells you that the TPS itself is not at fault (and thus causing the TPS trouble code). Without power, the TPS can't create a throttle angle voltage signal. Although beyond the scope of this tutorial, your next step is to diagnose and restore this missing power.

TEST 3: Verifying Throttle Position Sensor Has Ground

How To Test The Throttle Position Sensor (1986, 1987, 1988, 1989, 1990, 1991 S10/S15)

So far, you have confirmed that:

  1. You have a TPS trouble code lighting up the check engine light (CEL).
  2. The TPS is not creating a decreasing/increasing throttle angle voltage signal (TEST 1).
  3. That the GRY wire of the TPS connector has 4.5 to 5 Volts DC (TEST 2).

Now, we'll make sure that the black BLK wire of the TPS connector is feeding the TPS with ground.

IMPORTANT: Ground is provided directly by the fuel injection computer on your S10 or S15 pickup/SUV. Be careful and don't intentionally or accidentally short this wire (circuit) to battery power or you will fry the fuel injection computer.

OK, here are the test steps:

  1. 1

    Set your multimeter to Volts DC mode.

  2. 2

    Probe the BLK wire of the TPS connector. This is the wire that connects to TPS pin labeled with the letter A in the illustration above.

    Be careful not to damage the terminal if you probe it on the front of the connector. If possible, you should use a back probe or a wire-piercing probe to check this circuit.

  3. 3

    Now, with the red multimeter test lead, probe the battery positive (+) terminal.

  4. 4

    Turn the Key to its ON position but don't start the engine. This will power up the fuel injection computer.

  5. 5

    Your multimeter will display 11 to 12 Volts if the BLK wire is feeding the TPS with ground.

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

CASE 1: The multimeter confirms that the BLK wire is feeding Ground to the TPS. This test result confirms that the TPS is getting Ground from your S10's fuel injection computer.

Taking into account the test results of all 3 test, you have confirmed that:

  1. The TP sensor is not providing a varying voltage signal when manually opening the throttle plate.
  2. The TP sensor is being fed 5 Volts DC.
  3. The TP sensor is being fed ground.

Therefore, you can conclude that the throttle position sensor is bad and needs to be replaced (and that this will solve the TP sensor code lighting up the check engine light).

CASE 2: Multimeter confirms that the BLK wire IS NOT feeding Ground to the TPS. Double check that you're testing the correct TP sensor harness terminal wire and repeat the test.

If your test result still indicates that the TPS is not getting ground, then we can conclude that one of two things are causing this lack of ground:

  1. There's an open in the wire between the TP sensor harness connector and the fuel injection computer's harness connector.
  2. The fuel injection computer has an internal problem (although this is extremely rare).

Although testing these two conditions are beyond the scope of this article, you have now eliminated the throttle position sensor (TPS) on your 2.8L GMC/Chevy as being the cause of the problem and/or the TP sensor diagnostic trouble code (DTC) lighting up the check engine light (CEL).

Chevrolet Vehicles:

  • S10 Blazer 2.8L
    • 1986, 1987, 1988, 1989
  • S10 Pickup 2.8L
    • 1986, 1987, 1988, 1989, 1990, 1991

GMC Vehicles:

  • S15 Jimmy 2.8L
    • 1986, 1987, 1988, 1989

GMC Vehicles:

  • S10 Pickup 2.8L
    • 1986, 1987, 1988, 1989, 1990, 1991