How To Test The TPS (1989-1993 3.1L V6 Buick Regal, Oldsmobile Cutlass Supreme)

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.

ES 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: Goupchn 4mm Banana to Banana Plug Test Leads Kit (Amazon affiliate link).

Let's get started:

1. 1

   Place your multimeter in Volts DC mode.

2. 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. 3

   Connect the black multimeter test lead directly on the battery negative (-) post.

4. 4

   Turn the key to the ON position but don't crank or start the engine.

5. 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. 6

   The multimeter should show an increasing voltage as you (or your helper) open up the throttle plate.

7. 7

   Close the throttle plate as you observer the multimeter.

8. 8

   The multimeter should show a decreasing voltage as you begin to close the throttle plate.

9. 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.

TEST 2: Making Sure The TPS Is Receiving 5 Volts

Like every other electrical component on your vehicle, the throttle position sensor requires power and Ground to function.

In this section, we'll verify that the TPS is receiving 5 Volts DC from the fuel injection computer.

The wire that supplies that 5 Volts (from the computer to the TPS) is the wire labeled with the letter A in the photo above.

The wire that connects to the terminal labeled with the letter A is the TPS connector's grey (GRY) wire.

If the wire supplies 5 Volts DC to the TPS, the next step is ensuring that the sensor receives Ground (TEST 3).

Let's get testing:

1. 1

   Place your multimeter in Volts DC mode.

2. 2

   Disconnect the TPS from its electrical connector.

3. 3

   Turn the key the ON position but don't start the engine.

4. 4

   With the red multimeter test lead, gently probe the female terminal labeled with the letter A.
   
   Terminal A connects to the GRY wire of the connector.

5. 5

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

6. 6

   Your multimeter should read 4.5 to 5 Volts DC.

Let's analyze your test results:

CASE 1: The GRY wire is feeding the TPS with 5 Volts. This is the correct test result.

Now that you have confirmed that your 3.1L V6 Buick (Oldsmobile)'s TPS is getting 5 Volts, the next step is to make sure it's getting Ground. Go to: TEST 3: Making Sure That The TPS Is Receiving Ground.

CASE 2: The GRY wire IS NOT feeding the TPS with 5 Volts. Without these 5 Volts the TPS, on your 3.1L V6 Buick (Oldsmobile), will not function.

These missing 5 Volts are usually the result of an open-circuit problem in the GRY wire between the TPS sensor's connector and the fuel injection computer's connector.

TEST 3: Making Sure That The TPS Is Receiving Ground

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

• The TPS voltage signal does not increase/decrease when 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, let's check that the black (BLK) wire that connects to the terminal labeled with the letter B supplies Ground to the throttle position sensor.

IMPORTANT: Be careful not to short the Ground wire to battery power, or you'll fry the fuel injection computer. The multimeter voltage test suggested below (to test the Ground circuit) is a safe and accurate test.

These are the test steps:

1. 1

   Place your multimeter in Volts DC mode.

2. 2

   Disconnect the TPS from its electrical connector.

3. 3

   Turn the key the ON position but don't start the engine.

4. 4

   With the black multimeter test lead, gently probe the terminal labeled with the letter B.
   
   Terminal B connects to the BLK wire of the connector.

5. 5

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

6. 6

   Your multimeter should read 10 to 12 Volts DC.

Let's analyze your test results:

CASE 1: The BLK wire is feeding Ground to the TPS. This is the correct test result.

You can correctly conclude that the TPS is defective if you have:

• Confirmed that the TPS voltage signal does not increase/decrease as you opened/closed the throttle plate (TEST 1).
• Confirmed that the TPS is getting 5 Volts (TEST 2).
• Confirmed, in this test section, that the TPS is getting Ground.

CASE 2: The BLK wire IS NOT feeding Ground to the TPS. Without Ground the TPS will not function.

This missing Ground is usually caused by an open-circuit problem in the BLK wire between the throttle position sensor's connector and the fuel injection computer's connector.

More 3.1L Regal And Cutlass Supreme Tutorials

You can find a complete list of diagnostic tutorials for the 3.1L V6 Buick Regal and Oldsmobile Cutlass Supreme in this index:

• GM 3.1L Index of Articles.

Here's a sample of the tutorials you'll find there:

• How To Test The EGR Valve (1990-1993 3.1L V6 Buick Regal, Oldsmobile Cutlass Supreme).
• How To Test The Starter Motor (1989-1993 3.1L V6 Buick Regal, Oldsmobile Cutlass Supreme).
• How To Test The Fuel Pump (1989-1993 3.1L V6 Buick Regal, Oldsmobile Cutlass Supreme).
• How To Test Engine Compression (3.1L V6 Buick, Oldsmobile).