Here's a simplified throttle actuator control (TAC) system wiring diagram. Includes the electronic throttle body circuit diagram and the APP sensor assembly circuit diagram.

The TAC circuit wiring diagrams in this page apply only to the 2002, 2003, 2004, and 2005 4.2L Chevrolet TrailBlazer and GMC Envoy. You can find the TAC system wiring diagram for the 2006-2007 4.2L TrailBlazer And GMC Envoy here:

  1. TAC System Wiring Diagram (2006-2007 4.2L Chevrolet TrailBlazer).

Testing the electronic throttle body to see if its bad (or not) is not difficult at all. I've written the following tutorial explaining how to test TPS 1, TPS 2 and the throttle actuator motor: Electronic Throttle Body Tests (2002-2007 4.2L Chevrolet TrailBlazer).

You can find the APP sensor assembly tests (2002-2003 4.2L Chevy TrailBlazer and GMC Envoy only) here: How To Test APP Sensor 1 And 2 (2002-2003 4.2L Chevrolet TrailBlazer).

DIAGRAM 1: Electronic Throttle Body

PART 1: Electronic Throttle Body Wiring Diagram Of The TAC System-2002, 2003, 2004, 2005 4.2L Chevrolet TrailBlazer And GMC Envoy

DIAGRAM 2: APP Sensor 1 And 2

PART 2: APP Sensor 1 And APP Sensor 2 Wiring Diagram Of The TAC System -2002, 2003, 2004, 2005 4.2L Chevrolet TrailBlazer And GMC Envoy

More GM 4.2L Test Tutorials

If this tutorial was helpful/informative, you can find a complete list of tutorials here: GM 4.2L Index of Articles.

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

  1. How To Test For A Blown Head Gasket (2002-2009 4.2L Chevrolet TrailBlazer).
  2. How Often Should I Replace The Spark Plugs? (2002-2009 4.2L Chevrolet TrailBlazer).
  3. How To Test Engine Compression (2002-2009 4.2L Chevrolet TrailBlazer).
  4. How To Test APP Sensor 1 And 2 (2002-2003 4.2L Chevrolet TrailBlazer).
  5. Electronic Throttle Body Tests (2002-2007 4.2L Chevrolet TrailBlazer).