This tutorial will explain how to test the electronic throttle body on the 2002-2007 4.2L Chevrolet TrailBlazer and GMC Envoy.
You'll be able to find out if TPS 1 or TPS 2 is defective or not. We'll also test the throttle actuator motor.
You don't need any expensive diagnostic equipment to test the electronic throttle body since I'm going to show you how to resistance test the throttle position sensors and the throttle actuator motor using a multimeter.
NOTE: This tutorial applies to the 2002, 2003, 2004, 2005, 2006, and 2007 4.2L Chevrolet TrailBlazer or 4.2L GMC Envoy only.
Contents of this tutorial at a glance:
- Symptoms Of A Bad Electronic Throttle Body.
- Electronic Throttle Body Terminal Pin Out Chart.
- TEST 1: TPS 1 Resistance Test (Part 1 Of 2).
- TEST 2: TPS 1 Resistance Test (Part 2 Of 2).
- TEST 3: TPS 2 Resistance Test (Part 1 Of 2).
- TEST 4: TPS 2 Resistance Test (Part 2 Of 2).
- TEST 5: Testing The TAC Motor.
- Where To Buy The Electronic Throttle Body And Save.
- More GM 4.2L Test Tutorials.
You can find this tutorial in Spanish here: Cómo Probar El Cuerpo Del Acelerador Electrónico (2002-2007 4.2L Chevrolet TrailBlazer) (at: autotecnico-online.com).
NOTE: You can find the TAC system wiring diagram here:
- TAC System Wiring Diagram (2002-2005 4.2L Chevrolet TrailBlazer).
- TAC System Wiring Diagram (2006-2007 4.2L Chevrolet TrailBlazer).
If you need to test the APP sensor assembly (2002-2003 TrailBlazer and Envoy only), you can find the tutorial here: How To Test APP Sensor 1 And 2 (2002-2003 4.2L Chevrolet TrailBlazer).
Symptoms Of A Bad Electronic Throttle Body
As you're probably already aware, the electronic throttle body is made up of three components. These are TPS 1, TPS 2, and the throttle actuator motor (for the sake of our testing discussion I'm leaving out the throttle plate).
The throttle position sensors within the throttle body are tasked with informing the fuel injection computer of the throttle plate angle.
Since the electronic throttle body is a critical component of the engine's management system, when one of its throttle position sensors fail you'll see one or more of the following trouble codes.
- The check light engine light will be lit up by one of the following trouble codes:
- P0121: Throttle Position Sensor (TPS) Sensor 1 Perfomance.
- P0122: Throttle Position Sensor (TPS) Sensor 1 Circuit Low Voltage.
- P0123: Throttle Position Sensor (TPS) Sensor 1 Circuit High Voltage.
- P0222: Throttle Position Sensor (TPS) Sensor 2 Circuit Low Voltage.
- P0223: Throttle Position Sensor (TPS) Sensor 2 Circuit High Voltage.
- P2135: Throttle Position Sensor (TPS) Sensor 1 And 2 Correlation.
- Your Chevy TrailBlazer or GMC Envoy will run in Reduced Engine Power mode.
- The engine starts and runs but when you try to accelerate your Chevy TrailBlazer or GMC Envoy, it accelerates very slowly.
- The engine starts and runs but the engine does not accelerate when you step on the accelerator pedal.
- The engine starts and runs but shuts down.
Electronic Throttle Body Terminal Pin Out Chart
|A||DK GRN||TPS 1 Signal|
|B||LT BLU/BLK||5 Volts (TPS 2)|
|C||BLK||Ground (TPS 1)|
|D||PPL||TPS 2 Signal|
|E||YEL||Throttle Actuator Motor Control|
|F||BRN||Throttle Actuator Motor Control|
|G||GRY||5 Volts (TPS 1)|
|H||BLK/WHT||Ground (TPS 2)|
The connector on the throttle body itself has male spade terminals. The terminals on the electrical connector has female terminals.
All of the tests in this tutorial are done on the connector of the throttle body itself and this connector has male spade terminals.
TEST 1: TPS 1 Resistance Test (Part 1 Of 2)
Testing the throttle position sensors within the electronic throttle body simply involves testing the resistance between two terminals.
For our first test we're going to test the resistance of terminal C and terminal G of TPS 1.
Terminal C is the terminal that receives Ground from your Chevy Trailblazer or GMC Envoy's fuel injection computer.
Terminal G is the terminal that receives 5 Volts from the fuel injection computer.
What we're looking for is to make sure that this circuit hasn't suffered an open-circuit or short-circuit problem.
If there's an open-circuit problem between them you're not going to see continuity at all on your multimeter. If you're using a digital multimeter you're going to see the letters OL displayed on your multimeter's screen.
If there's a short-circuit problem between them you're going to see an Ohm reading of less than 1 Ohm on your multimeter.
NOTE: All multimeter connections are done on the male spade terminals of the electronic throttle body itself.
TIP: The easiest way that I've found to test the resistance between the terminals is to connect the multimeter test leads to the terminals with jumper wires that have alligator clips on both ends (see photo 2 of 2 in the image viewer above).
These are the test steps:
Disconnect the throttle body from its electrical connector.
Place your multimeter in Ohms mode.
Connect the red multimeter test lead to terminal C.
Connect the black multimeter test lead to terminal G.
Your multimeter should read continuity.
At this point I have gotten about 3 K Ohms from a good TPS 1.
Let's examine your test results:
CASE 1: The multimeter registered continuity between terminals C and G. This is the correct test result.
So far so good. The next test is to test the resistance between terminals A and G as you open and close the throttle plate: TEST 2: TPS 1 Resistance Test (Part 2 Of 2).
CASE 2: The multimeter DID NOT register continuity between terminals C and E. This lets you know that TPS 1 is defective within the electronic throttle body. With this test result you can conclude that the electronic throttle body needs to be replaced.