How To Test The TPS (1987-1993 2.5L Chevrolet S10, GMC S15, GMC Sonoma)

TEST 2: Making Sure The TPS Is Receiving 5 Volts

If the throttle position sensor voltage signal did not increase/decrease while you opened/closed the throttle plate in TEST 1, there's a good chance it is not receiving 5 Volts from the fuel injection computer.

To rule out this possibility, the focus of this test section is to confirm that the terminal labeled with the letter A is supplying 5 Volts to the throttle position sensor.

The wire that connects to terminal A is the gray (GRY) wire of the TPS sensor's 3-wire connector.

Let's get rolling:

1. 1

   Select Volts DC mode on your multimeter.

2. 2

   Disconnect the TP sensor from its connector.

3. 3

   Probe the grey (GRY) wire with the red multimeter test lead and an appropriate tool.
   
   The GRY wire connects to the terminal labeled with the letter A in the photo above.
   
   NOTE: You can probe the front of the terminal with your multimeter test lead. Just be careful not to damage the female terminal.

4. 4

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

5. 5

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

6. 6

   The multimeter should report 4.5 to 5 Volts DC.

Let's interpret your test results:

CASE 1: The GRY wire is delivering 4.5 to 5 Volts. This is the correct test result and confirms the TPS is getting power.

Your next and last step is to see if the TPS is getting Ground. Go to: TEST 3: Making Sure The TPS Is Receiving Ground.

CASE 2: The GRY wire IS NOT delivering 4.5 to 5 Volts. Without power the TPS will not function.

Although it's beyond the scope of this tutorial, your next step is to find out why this voltage is missing and restore it.

TEST 3: Making Sure The TPS Is Receiving Ground

Up to this point, your TPS diagnostic tests have confirmed the following:

• A TPS diagnostic trouble code illuminates the check engine light.
• The TPS voltage signal is stuck at one value as you open/close the throttle plate (TEST 1).
• The TPS is receiving 5 Volts from the fuel injection computer (TEST 2)

For our final test, we'll make sure that the TPS is receiving Ground from the fuel injection computer.

The wire that delivers this Ground is the black (BLK) wire of the TPS sensor's 3-wire connector.

In the photo above, I've labeled the terminal that connects to the BLK wire with the letter B.

To check for the presence of Ground in the black wire, we'll do a multimeter voltage test.

IMPORTANT: The fuel injection computer is the component that supplies Ground to the throttle position sensor. Be careful and do not short-circuit the Ground wire to 12 Volts or you'll fry the computer. The suggested multimeter voltage test is a safe way to test for the presence of Ground in the wire.

These are the test steps:

1. 1

   Select Volts DC mode on your multimeter.

2. 2

   Disconnect the TP sensor from its connector.

3. 3

   Probe the black (BLK) wire with the black multimeter test lead and an appropriate tool.
   
   The BLK wire connects to the terminal labeled with the letter B in the photo above.
   
   NOTE: You can probe the front of the terminal with your multimeter test lead. Just be careful not to damage the female terminal.

4. 4

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

5. 5

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

6. 6

   The multimeter should display 10 to 12 Volts DC.

Let's interpret your test results:

CASE 1: Your multimeter registered 10 to 12 Volts. This is the correct test result and confirms the TPS is getting Ground.

You can conclude the TPS is bad if you have:

• Confirmed the TPS voltage signal is stuck at one value as you open/close the throttle plate (TEST 1).
• Confirmed the TPS is receiving 5 Volts from the fuel injection computer (TEST 2)
• Confirmed the TPS is receiving Ground from the fuel injection computer (this test section).

CASE 2: Your multimeter DID NOT register 10 to 12 Volts. Without Ground the TPS will not function.

Although it's beyond the scope of this tutorial, your next step is to find out why Ground is missing and restore it.