How To Test The Throttle Position Sensor (1986-1991 2.8L S10/S15)

By: Abraham Torres-Arredondo
Created: 08 December 2014
Updated: 18 March 2024
Articl Id: 496

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TEST 2: Making Sure The TPS Is Getting Power

Making Sure The TPS Is Getting Power. How To Test The Throttle Position Sensor (1986, 1987, 1988, 1989, 1990, 1991 2.8L V6 Chevrolet S10 Pickup, GMC S15 Pickup, GMC Sonoma)

In this test section, we're going to check that the TPS is getting 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
Disconnect the TPS from its electrical connector.
2
Set your multimeter to Volts DC mode.
3
Connect the black multimeter test lead to the negative (-) battery terminal.
4
With the red multimeter test lead, probe the female terminal (of the connector) that connects to the GRY wire.

IMPORTANT: Be careful when probing the metal terminal of the TPS connector. Damaging the terminal will require that you replace the connector.
5
Turn the key to the ON position but don't crank or start the engine.
6
Your multimeter should display 4.5 to 5 Volts on its screen.

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: Making Sure The TPS Is Getting 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: Making Sure The TPS Is Getting Ground

Making Sure The TPS Is Getting Ground. How To Test The Throttle Position Sensor (1986, 1987, 1988, 1989, 1990, 1991 2.8L V6 Chevrolet S10 Pickup, GMC S15 Pickup, GMC Sonoma)

So far, you have confirmed that:

You have a TPS trouble code lighting up the check engine light (CEL).
The TPS is not creating a decreasing/increasing throttle angle voltage signal (TEST 1).
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
Disconnect the TPS from its electrical connector.
2
Set your multimeter to Volts DC mode.
3
Connect the red multimeter test lead to the positive (+) battery terminal.
4
With the black multimeter test lead, probe the female terminal (of the connector) that connects to the BLK wire.

IMPORTANT: Be careful when probing the metal terminal of the TPS connector. Damaging the terminal will require that you replace the connector.
5
Turn the key to the ON position but don't crank or start the engine.
6
Your multimeter should display 10 to 12 Volts on its screen.

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:

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

After replacing the TPS, you'll need to adjust it. You can find the instructions here: How To Adjust The TPS.

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:

There's an open-circuit problem in the wire between the TP sensor harness connector and the fuel injection computer's harness connector.
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).

How To Adjust The TPS

The TPS, on the 1986 to 1991 S10 and S15 vehicles covered by this tutorial, has to be adjusted if removed and replaced.

The adjustment procedure is easy and below you'll find it explained in a step-by-step way:

Tap into the DK BLU wire of the TPS with the red multimeter test lead.
- The TP sensor must remain connected to its connector during the whole adjustment procedure.
Ground the black multimeter test lead on the battery negative (-) terminal.
Turn the key ON but don't crank or start the engine.
Your multimeter should read 0.42 to 0.45 Volts DC with the throttle plate closed.
- If the multimeter does not read 0.42 to 0.45 Volts DC, then the TPS is not adjusted to specification.
To adjust the TPS:
- Loosen the TPS screws.
- Rotate the TPS till your multimeter registers 0.42 to 0.45 Volts and tighten the screws.
After tightening the TPS screws, check the voltage reading on the DK BLU wire to make sure it's within the indicated specification.
After the adjustment is done, disconnect the battery negative (-) cable from the battery to reset the fuel injection computer. This is a very important step for the computer to recognize the new closed throttle plate angle voltage value as 0 degrees!