As you already know, the throttle position sensor (TPS) is responsible for sending a signal to the engine control module (ECM) indicating the position of the throttle plate as you step on or step off the accelerator pedal.
The cool thing is that you can accurately the TPS with a multimeter on your 1991-1993 2.8L V6 Chevy S10 pickup (GMC Sonoma).
In this tutorial, I'll provide a step-by-step explanation of the TPS test and explain how to determine if the TPS sensor is working properly.
Contents of this tutorial:
- Symptoms Of A Bad Throttle Position Sensor.
- Throttle Position Sensor (TPS) Circuit Descriptions.
- Where To Buy Your Throttle Position Sensor And Save.
- TEST 1: Testing The Throttle Position Sensor Voltage Signal.
- TEST 2: Making Sure Throttle Position Sensor Is Getting Power.
- TEST 3: Making Sure Throttle Position Sensor Is Getting Ground.
- More 2.8L Chevy S10 Pickup, GMC S15 Pickup, And GMC Sonoma Tutorials.
APPLIES TO: This tutorial applies to the following vehicles:
- 2.8L Chevrolet S10 Pickup: 1991, 1992, 1993.
- 2.8L GMC Sonoma: 1991, 1992, 1993.
NOTE: For the 1986 to 1991 TPS test, go to: How To Test The Throttle Position Sensor (19986-1991 2.8L S10/S15).
You can find this tutorial in Spanish here: Cómo Probar El Sensor TPS (1991-1993 2.8L S10 Pick Up) (at: autotecnico-online.com).
Symptoms Of A Bad Throttle Position Sensor
The on-board diagnostic (OBD) system in your 2.8L S10 pickup (Sonoma) is designed to notify you of any sensor failures by illuminating the check engine light (CEL).
The TPS is one of the sensors monitored by the fuel injection computer, and when it malfunctions, the computer will illuminate the CEL to let you know.
You'll see one of the following TPS trouble codes stored in the computer's memory:
- Code 21: Throttle Position Sensor Signal Voltage High.
- Code 22: Throttle Position Sensor Signal Voltage Low.
You'll also see one or more of the following symptoms:
- Your vehicle fails the smog check (state mandated emissions test).
- Bad gas mileage.
- Hard start and/or extended cranking time (after shut off).
- Black smoke coming out of the tailpipe.
- Hesitation when accelerating your vehicle down the road.
Thankfully, the TPS can be tested without a scan tool!
Throttle Position Sensor (TPS) Circuit Descriptions
There are 3 wires sticking out of the throttle position sensor's connector. Each one has a specific task to do. To be able to test the TPS, we need to know what each one does.
The following is a brief description of what each wire does:
| Terminal | Wire | Description |
|---|---|---|
| A | Grey (GRY) | 5 Volts |
| B | Black (BLK) | Ground |
| C | Blue (BLU) | TPS Signal |
Where To Buy Your TP Sensor And Save
Where can you buy the original AC Delco TP sensor for your 2.8L Chevy S10 Pick Up? You can buy it at your local auto parts store but it's gonna' cost a whole lot more. I suggest taking a look at the price of the TP sensor in the following links and compare:
Not sure if the above TP sensor fits your particular 2.8L Chevy S10 pickup? Don't worry, once you get to the site, they'll make sure it fits by asking you the particulars of your vehicle. If it doesn't fit, they'll find you the right one.
TEST 1: Testing The Throttle Position Sensor Voltage Signal
The job of the throttle position sensor is to inform the fuel injection computer of the angle of the throttle plate opening or closing.
As the throttle plate opens, the TPS voltage signal increases. When the throttle plate closes, the voltage signal decreases.
The throttle angle voltage signal is sent to the fuel injection computer via the wire connected to the terminal labeled letter C in the illustration above.
Our first task to see if the TPS is working properly or not, is to tap into the signal wire with a multimeter and see if the TPS produces a correct throttle angle voltage signal when we manually open and close the throttle plate.
NOTE: The throttle position sensor has to remain connected to its connector for this test to work (this is where a wire piercing probe comes in handy to get to the signal inside the wire. To see what one looks like, click here: Wire Piercing Probe Tool).
OK, let's start:
PART 1:
- 1
Turn the key to the ON position but don't start the engine.
- 2
Place your multimeter in Volts DC mode.
- 3
Connect the red multimeter test lead to the blue (BLU) wire of the TP sensor harness connector.
The BLU wire connects to the terminal identified with the letter C in the photo above. - 4
Connect the black multimeter test lead to the battery negative (-) terminal.
NOTE: The TP sensor must remain connected to its electrical connector. You'll need to use a back probe or a wiring piercing probe to tap into the signal of the wire. To see what a wire piercing probe looks like and where to buy one, go here: Wire Piercing Probe. - 5
Your multimeter should report a voltage between 0.2 to 0.9 Volts DC with the throttle plate closed.
If your multimeter doesn't, don't worry about it just yet, continue with the other steps.
PART 2:
- 6
Slowly open the throttle plate (by hand from the engine compartment).
- 7
The voltage value should increase as the throttle plate opens.
This increase in voltage should be smooth and without any gaps or skips.
Once the throttle is wide open, your multimeter should read somewhere between 3.5 to 4.5 Volts DC. - 8
Slowly close the throttle plate.
- 9
As the throttle plate is closing, you should see the voltage decrease smoothly and without any gaps or skips, to the same voltage you noticed in step 5.
PART 3:
- 10
Lightly tap on the throttle position sensor with the handle of a screw-driver or something similar (I want to emphasize the words 'lightly tap') as you slowly open and close the throttle and observe the multimeter.
If the TPS is bad, the tapping will cause the voltage numbers to skip or go blank. If the TPS is OK, the tapping will have no effect on the voltage numbers. - 11
Repeat step 10 several times to make sure of your multimeter test results.
Let's take a look at your test results:
CASE 1: The throttle angle voltage increased and decreased as you opened and closed the throttle plate. This test result confirms that the TP sensor is OK and not defective.
CASE 2: The throttle angle voltage DID NOT increase/decrease as you opened/closed the throttle plate. This test result confirms that the TPS is behind the TPS trouble code lighting up the check engine light (CEL) on your 2.8L V6 Chevrolet S10 pickup (GMC Sonoma).
The next step is to check that the TPS is getting power. Go to: TEST 2: Making Sure Throttle Position Sensor Is Getting Power.
CASE 3: The multimeter DID NOT register any voltage. This test result doesn't condemn the TP sensor as bad just yet.
Why? Because the TP sensor may be missing either power or Ground. So the next step is to check that the TP sensor is getting power. Go to: TEST 2: Making Sure Throttle Position Sensor Is Getting Power.
