The 1999-2002 V8 Chevrolet Silverado and GMC Sierra come equipped with an old-style throttle position sensor -no electronic throttle body.
In this tutorial, I'll explain how to test the TPS with a multimeter. With 3 simple tests you'll be able to find out if it's bad or not.
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 Has 5 Volts.
- TEST 3: Making Sure The TPS Has Ground.
- More Silverado, Sierra, Suburban, Tahoe, And Yukon Tutorials.
You can find this tutorial in Spanish here: Cómo Probar El Sensor TPS (1999-2002 V8 Silverado, Sierra, Suburban, Tahoe, Yukon) (at: autotecnico-online.com).
NOTE: This tutorial applies to the following vehicles since they use the exact same throttle position sensor:
Chevrolet:
- Silverado (1500, 2500):
- 4.8L, 5.3L: 1999, 2000, 2001, 2002
- Silverado (2500):
- 6.0L: 1999, 2000, 2001, 2002
- Suburban (1500):
- 5.3L: 2000, 2001, 2002
- Suburban (2500):
- 6.0L: 2000, 2001, 2002
- Tahoe:
- 4.8L, 5.3L: 2000, 2001, 2002
GMC:
- Sierra (1500, 2500):
- 4.8L, 5.3L: 1999, 2000, 2001, 2002
- Sierra (2500):
- 6.0L: 1999, 2000, 2001, 2002
- Yukon:
- 4.8L, 5.3L: 2000, 2001, 2002
- Yukon XL (1500):
- 5.3L: 2000, 2001, 2002
- Yukon XL (2500):
- 6.0L: 2000, 2001, 2002
RELATED TROUBLE CODES:
- P0121 -What Does It Mean? (1999-2002 V8 Silverado, Sierra, Suburban, Tahoe, Yukon).
- P0122 -What Does It Mean? (1999-2002 V8 Silverado, Sierra, Suburban, Tahoe, Yukon).
- P0123 -What Does It Mean? (1999-2002 V8 Silverado, Sierra, Suburban, Tahoe, Yukon).
Symptoms Of A Bad Throttle Position Sensor
It's the throttle position sensor's job to measure the throttle plate angle as it opens or closes as you step on or off the accelerator pedal.
In a nutshell, the throttle position sensor produces a voltage signal that increases as you step on the accelerator pedal and the throttle plate opens.
As you step off the accelerator pedal, the throttle plate starts to close and the TPS voltage signal decreases back to its original base voltage.
All of these throttle plate angle changes are constantly reported to the fuel injection computer on your Chevrolet Silverado (GMC Sierra).
Since the throttle position sensor (TPS) is such an important component of the engine management system, when it fails you're gonna' definitely feel the engine resent it.
You're going to see the following TPS diagnostic trouble code lighting up the check engine light:
- P0121 Throttle Position Sensor Performance Problem.
- P0122 TPS Voltage Too Low.
- P0123 TPS Voltage Too High.
You're also going to see one or more of the following symptoms:
- Won't pass the state mandated emissions test.
- Bad gas mileage.
- Lack of power, rough idle, or hesitation.
- Engine cranks a long time before starting.
Throttle Position Sensor (TPS) Circuit Descriptions
Below are the circuit descriptions of the 3 wires of the throttle position sensor's connector.
| Terminal | Wire | Description |
|---|---|---|
| A | Grey (GRY) | 5 Volts |
| B | Black (BLK) | Sensor Ground |
| C | Dark Blue (DK BLU) | TPS Signal |
Where To Buy The TPS And Save
The TPS, on the 1999-2002 V8 Chevrolet Silverado (GMC Sierra) is a pretty inexpensive component.
The following links will help you to comparison shop and hopefully save you a few bucks on its purchase (AC-Delco is the original equipment manufacturer):
NOTE: The above throttle position sensor (TPS) fits the following vehicles: 1999, 2000, 2001, 2002 V8 Chevrolet Silverado and GMC Sierra.
TEST 1: Testing The TPS Voltage Signal
To get the TPS diagnostic on the way, we're gonna' make sure that the throttle position sensor's voltage signal increases/decreases as the throttle plate is opened.
If the throttle position sensor is bad, it'll stay stuck producing one voltage value as the throttle plate is opened/closed.
IMPORTANT: The throttle position sensor (TPS) must remain connected to its electrical connector for this test to function properly. To be able to access the voltage inside the signal wire, you'll need to use either a back probe or a wire piercing probe. You can see an example of this tool 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 is identified with the letter C in the photo above. - 3
Ground the black multimeter test lead directly on the battery negative (-) post.
- 4
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. - 5
The multimeter should show an increasing voltage as you (or your helper) open up 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 a decreasing voltage as you begin to close the throttle plate.
- 7
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 red wire is feeding the TPS with 5 Volts. For this test go to: TEST 2: Making Sure The TPS Has 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 red wire is feeding the TPS with 5 Volts. For this test go to: TEST 2: Making Sure The TPS Has 5 Volts.
