Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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HOMESERVICE MANUALSCHEVROLET2003TRAILBLAZER 4.2 S, 4WDREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 18 (BODY CONTROL MODULES)SELF-DIAGNOSTIC SYSTEMTHEFT DETERRENT SYSTEM DIAGNOSTIC SYSTEM CHECK
2003 Chevrolet TrailBlazer 4.2 S, 4WD
Theft Deterrent System Diagnostic System Check
2003 Chevrolet TrailBlazer 4.2 S, 4WDSECTION Theft Deterrent System Diagnostic System Check
WARNING: This page does not describe the selected car, but rather 8 other vehicles, including the 2002 GMC Savana, 2002 Chevrolet Chevy Express, 2001 GMC Savana Special, 2001 GMC Savana Camper Special, and 2001 GMC Savana. However, it is still accessible from the selected car via links, so may be relevant.
NOTE:
Vehicle Theft Deterrent (VTD) module may also be referred to as Passlock(tm) module.
- Turn ignition switch to OFF position. Connect scan tool to Data Link Connector (DLC), located below steering column. Turn ignition switch to RUN position. If scan tool powers up, go to next step. If scan tool does not power up, go to TEST A: SCAN TOOL DOES NOT POWER UP under SYSTEM TESTS.
- Using scan tool, attempt to communicate with Powertrain Control Module (PCM) and Passlock(tm) module. If scan tool communicates with PCM and Passlock(tm) module, go to next step. If scan tool does not communicate with PCM or Passlock(tm) module, see TEST B: SCAN TOOL DOES NOT COMMUNICATE WITH CLASS 2 DEVICE under SYSTEM TESTS.
- Select DISPLAY DTCs function on scan tool for PCM and Passlock(tm) module. If scan tool displays any DTCs go to step 5 . If can tool does not display any DTCs, go to next step.
- Momentarily rotate ignition switch to CRANK position, but do not start engine. Release ignition switch to RUN position. Using scan tool, observe PASSLOCK CODE in PASSLOCK MODULE SECURITY DATA LIST. If scan tool displays OPEN, take actions for DTC B2958. See appropriate ANTI-THEFT SYSTEMS article. See DIAGNOSTIC TROUBLE CODE DEFINITIONS . If scan tool does not display OPEN, repair by symptom. See ANTI-THEFT SYSTEMS - CHEVY EXPRESS & SAVANA article.
- If scan tool displays DTCs which begin with "U", see TEST B: SCAN TOOL DOES NOT COMMUNICATE WITH CLASS 2 DEVICE under SYSTEM TESTS. If other DTCs are displayed, go to next step.
- If other DTCs are recorded, go to next step. If scan tool displays DTCs P0601, P0602, P0603, P0604, P0605, P0606, P1612 or P1627, see appropriate SELF-DIAGNOSTICS article in ENGINE PERFORMANCE.
- If scan tool displays DTC B1007, go to DTC B1007: CHECKSUM VALUE ERROR under DIAGNOSTIC TESTS.
- If scan tool displays DTC P0562, P0563, P1637, or P1638, go to DIAGNOSTIC TROUBLE CODE DEFINITIONS .
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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.