I think you'll be surprised how easy it is to test the throttle position sensor (TPS) on the 3.3L V6 equipped Pontiac Grand Am.
In this tutorial, you'll find the throttle position sensor test explained in a step-by-step matter. You'll easily find out if the sensor is bad or not with your test results.
This tutorial will also help you to diagnose the following OBD1 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 The TPS Is Getting Ground.
- More 3.3L Pontiac Grand Am Tutorials.
You can find this tutorial in Spanish here: Cómo Probar El Sensor TPS (1992-1993 3.3L V6 Pontiac Grand Am) (at: autotecnico-online.com).
APPLIES TO: This tutorial applies to the following vehicles:
- 3.3L V6 Pontiac Grand Am: 1992, 1993.
Symptoms Of A Bad Throttle Position Sensor
The fuel injection computer relies on the input from the TPS to managed quite a few engine management operations as the engine runs.
As such, when the TPS fails, engine performance and driveability will suffer.
You'll see one of the following OBD I trouble codes lighting up 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.
To find out more about the throttle position sensor, check out this article: What Does The TPS Do? (3.3L V6 Pontiac Grand Am).
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 | Blue (BLU) | TPS Signal |
| C | Black (BLK) | Ground |
Where To Buy The TPS And Save
The 1992 3.3L Pontiac Grand Am uses an adjustable TPS. The 1993 3.3L Pontiac Grand Am uses a non-adjustable TPS. They are not interchangeable.
The following links will help you to comparison shop for the throttle position sensor (of known professional automotive brands -NO knockoffs) for your 3.3L Pontiac Grand Am:
1992 Adjustable TPS
1993 Non-Adjustable TPS
TEST 1: Testing The TPS Voltage Signal
We're going to start our TPS diagnostic tests by checking the signal output of the throttle position sensor.
If the TPS is functioning correctly, its voltage signal should increase as the throttle plate is opened and then decrease as the throttle plate is closed.
The wire that carries the TPS voltage signal, and the one we're gonna' test, is the blue (BLU) wire of the sensor's 3 wire connector.
IMPORTANT: The throttle position sensor must remain connected to its connector to be able to access the signal inside the wire. You'll need to use either a wire piercing probe or a back probe. You can check out what this tool looks like, and where to buy it, here: Wire Piercing Probe.
Alright, let's get started:
- 1
Place your multimeter in Volts DC mode.
- 2
Connect the red multimeter test lead to the blue (BLU) wire of the TP sensor harness connector.
The terminal that connects to the BLU wire is identified with the letter B in the photo above.
NOTE: The TPS must remain connected to its connector to access 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.
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 the throttle plate.
- 7
The multimeter should show a decreasing voltage as you begin to close the throttle plate.
- 8
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 examine 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.
This test result also tells you that the TP sensor is getting 5 Volts DC 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 TP 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 TP sensor is defective.
To make sure the TP 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.
