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HOMESERVICE MANUALSCHEVROLET2003TRAILBLAZER 4.2 S, 4WDREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 704 (CELLULAR COMMUNICATION SYSTEM)REPAIR INSTRUCTIONSONSTAR® VEHICLE COMMUNICATION UNIT (VCU) REPLACEMENTINSTALLATION PROCEDURE
2003 Chevrolet TrailBlazer 4.2 S, 4WD

Installation Procedure

2003 Chevrolet TrailBlazer 4.2 S, 4WDSECTION Installation Procedure
WARNING: This page is about a different car, the 2002 GMC Sierra, 2002 GMC Cab & Chassis Sierra, 2002 Chevrolet Silverado, and 2002 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.
  1. Record the 11-digit ESN from the label on the new VCU module.
    NOTE: In order to avoid damage to the circuit board, do NOT over-tighten the thumb screws. Using your fingers, apply only a light pressure.
  2. Install the VCU to the bracket.
  3. Connect the electrical connectors to the VCU.
  4. Install the screw. Tighten the screw to 9 N.m (80 lb in).
  5. Install the IP cluster harness.
  6. Install the IP trim panel. Refer to TRIM PANEL REPLACEMENT - INSTRUMENT PANEL (I/P) UPPER .
  7. Press and hold the "end call" button, which is a black button with a white dot. The OnStar® status light will change from green to red to green.
  8. Contact the OnStar® Dealer support line by pressing the blue OnStar® button twice. The 11-digit ESN number will be needed by the OnStar® advisor.
RENDER: 1.0x

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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • • You smell fuel, burning insulation, or see smoke.
  • • Brakes feel soft, pull hard to one side, or make grinding noises.
  • • The engine overheats, stalls repeatedly, or misfires under load.
  • • You are missing required tools, torque specs, or safe lifting equipment.
  • • You are not confident in the next step or safety outcome.