As you probably already know, the throttle position sensor (TPS) is the component that the fuel injection computer uses to detect throttle angle.
Sooner or later, the TPS will fail. Luckily, the throttle position sensor is not difficult to test with a multimeter.
In this tutorial, I'll explain how to test the TPS. With your test results, you'll easily diagnose the TPS as good or bad and 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:
You can find this tutorial in Spanish here: Cómo Probar El Sensor TPS (1989-1993 3.1L Buick Regal, Oldsmobile Cutlass Supreme) (at: autotecnico-online.com).
APPLIES TO: This tutorial applies to the following vehicles:
- 3.1L Buick Regal: 1989, 1990, 1991, 1992, 1993.
- 3.1L Oldsmobile Cutlass Supreme: 1989, 1990, 1991, 1992, 1993.
Symptoms Of A Bad Throttle Position Sensor
The throttle position sensor is a critical component of the engine management system. So when it fails, you'll definitely notice that something is wrong.
You'll see one of the following OBD I TPS diagnostic trouble codes illuminating the check engine light:
- 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
I'm sure you've already noticed that the throttle position sensor has three wires coming out of its pigtail connector.
Each wire has a specific role, and the table below gives a brief description of each:
| 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 following links will help you comparison shop for the throttle position sensor (of known professional automotive brands- NO knock-offs) for your 3.1L V6 Buick (Oldsmobile).
TEST 1: Testing The TPS Voltage Signal
The throttle position sensor generates a voltage signal that increases as the throttle plate opens and decreases as it returns to its closed position.
The cool thing is that you and I can use a multimeter to check if the TPS signal is increasing/decreasing.
The wire we'll be connecting the multimeter to is the dark blue (DK BLU) wire.
The DK BLU wire connects to the female terminal marked with the letter C in the photo above.
IMPORTANT: The throttle position sensor must remain connected to its connector in order to access the signal in the wire. It would be best to use either a wire piercing probe or a back probe. 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 screw-driver's handle.
Let's analyze 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 sensor 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 sensor is defective.
To make sure the TPS sensor 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 sensor is defective.
To make sure the TPS sensor 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.
