Testing the throttle position sensor (TPS) isn't difficult as it can be tested with a multimeter. So yeah, you don't need any special testing equipment to test the TPS.
In this tutorial, I'll explain how step by step. With your test results, you'll quickly find out if the TPS is faulty.
In addition, you'll also diagnose the following OBD I trouble codes:
- Code 21: Throttle Position Sensor Signal Voltage High.
- Code 22: Throttle Position Sensor Signal Voltage Low.
Contents of this tutorial at a glance:
- Symptoms Of A Bad Throttle Position Sensor.
- Throttle Position Sensor (TPS) Circuit Descriptions.
- Where To Buy The TPS And Save.
- TEST 1: Testing The TPS Voltage Signal.
- TEST 2: Making Sure The TPS Is Receiving 5 Volts.
- TEST 3: Making Sure That The TPS Is Receiving Ground.
- More 3.1L Chevrolet And Pontiac Diagnostic Tutorials.
You can find this tutorial in Spanish here: Cómo Probar El Sensor TPS (1989-1993 3.1L V6 Chevrolet y Pontiac) (at: autotecnico-online.com).
APPLIES TO: This tutorial applies to the following vehicles:
- 3.1L Chevrolet Beretta: 1990, 1991, 1992, 1993.
- 3.1L Chevrolet Cavalier: 1990, 1991, 1992, 1993, 1994.
- 3.1L Chevrolet Celebrity: 1990.
- 3.1L Chevrolet Corsica: 1990, 1991, 1992, 1993.
- 3.1L Chevrolet Lumina: 1990, 1991, 1992, 1993, 1994.
- 3.1L Pontiac 6000: 1989, 1990, 1991.
- 3.1L Pontiac Grand Prix: 1989, 1990, 1991, 1992, 1993.
- 3.1L Pontiac Sunbird: 1991, 1992, 1993, 1994.
Symptoms Of A Bad Throttle Position Sensor
The fuel injection computer monitors the TPS. So when it fails, the computer will set a TPS diagnostic trouble code and illuminate the check engine light.
You'll see one of the following trouble codes stored in the computer's memory:
- 21: Throttle Position Sensor Signal Voltage High.
- 22: Throttle Position Sensor Signal Voltage Low.
You're also going to see one or more of the following symptoms:
- Engine hesitates when you step on the accelerator pedal.
- Lack of power when accelerating the vehicle.
- Bad gas mileage.
- Engine idle either too high or too low.
- Rough engine idle.
- The engine may start and immediately stall.
- The engine cranks but does not start.
Throttle Position Sensor (TPS) Circuit Descriptions
If you look at the TPS, you'll notice that three wires are coming out of its electrical connector.
Each wire plays a different role (than the other), and to successfully test the TPS, we need to know what each wire does.
The table below provides a brief description of the function of each wire:
| Terminal | Wire | Description |
|---|---|---|
| A | Grey (GRY) | 5 Volts |
| B | Dark Blue (DK BLU) | TPS Signal |
| C | Black (BLK) | Ground |
Where To Buy The TPS And Save
The TPS is not an expensive fuel injection system component. The following links will help you to compare the price of the TPS of popular automotive brands (you should avoid fake/knock-off parts).
TEST 1: Testing The TPS Voltage Signal
The TPS generates an increasing voltage signal when the throttle opens. As the throttle begins to close, the voltage signal decreases.
If the throttle position sensor is bad, the sensor will not generate this rising/falling voltage signal.
Knowing this, our first test is to hook up the multimeter to the dark blue (DK BLU) wire and see if the TPS produces a voltage signal that ramps up and down as the throttle opens and closes.
IMPORTANT: The throttle position sensor must remain connected to its connector in order to access the signal in the wire. I suggest you use either a wire piercing probe on the wire or a back probe on the connector. You can see what this tool looks like and where to buy it here: Wire Piercing Probe.
Let's get started:
- 1
Place your multimeter in Volts DC mode.
- 2
Connect the red multimeter test lead to the dark blue (DK BLU) wire of the TP sensor harness connector.
The DK BLU wire connects to the terminal labeled with the letter C in the photo above.
NOTE: The TPS must remain connected to its connector to test the TPS voltage signal. - 3
Connect the black multimeter test lead directly on the battery negative (-) post.
- 4
Turn the key on but don't crank or start the engine.
- 5
Manually rotate the throttle plate to its open position.
You'll get the best results by opening and closing the throttle plate directly on the throttle body instead of stepping on the accelerator pedal. - 6
The multimeter should show an increasing voltage as you (or your helper) open up the throttle plate.
- 7
Close the throttle plate as you observer the multimeter.
- 8
The multimeter should show a decreasing voltage as you begin to close the throttle plate.
- 9
Using a screwdriver's handle, gently tap the TP sensor as you open and close the throttle plate and observe the multimeter.
The purpose (of tapping the TP sensor with the screwdriver's handle) is to see if the TP sensor shows gaps in the voltage signal. Why? Because a good TP sensor will show a continuous increasing or decreasing voltage signal even while getting tapped by the screwdriver's handle.
Let's interpret your test results:
CASE 1: The TPS voltage signal increased/decreased as you opened/closed the throttle plate. This is the correct test result and it indicates that the throttle position sensor is good.
With this test result you can also conclude that the TPS is getting both power (5 Volts) and Ground from the fuel injection computer.
CASE 2: The TPS voltage signal DID NOT increase/decrease as you opened and closed the throttle plate. This test result usually indicates that the TPS is defective.
To make sure the TPS is bad the next step is to check that the GRY wire is feeding the TPS with 5 Volts. For this test go to: TEST 2: Making Sure The TPS Is Receiving 5 Volts.
CASE 3: The multimeter DID NOT register any voltage. This test result usually indicates that the TPS is defective.
To make sure the TPS is bad the next step is to check that the GRY wire is feeding the TPS with 5 Volts. For this test go to: TEST 2: Making Sure The TPS Is Receiving 5 Volts.
