Diagnostic Procedure

2003 Chevrolet TrailBlazer 4.2 S, 4WDSECTION Diagnostic Procedure
WARNING: This page is about a different car, the 2003 GMC Sierra, 2003 GMC Cab & Chassis Sierra, 2003 Chevrolet Silverado, and 2003 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.
  1. If SIR Diagnostic System Check has been performed, go to next step. If SIR Diagnostic System Check has not been performed, go to SIR DIAGNOSTIC SYSTEM CHECK .
  2. If PPS was replaced, go to next step. If PPS was not replaced, go to step  4.
  3. Inspect PPS and verify correct PPS was installed using PPS part number. If PPS is correct, go to next step. If PPS is not correct, go to step  6.
  4. If SDM was replaced, go to next step. If SDM was not replaced, go to step  8.
    NOTE: Use Digital Multimeter (J-39200) and Connector Test Adapter Kit (J-35616-A) or Flat WIre Probe Adapter Kit (J-42675) when performing electrical tests.
  5. Inspect SDM and verify correct SDM was installed using SDM part number. If SDM is correct, go to next step. If SDM is not correct, go to step  8.
  6. Replace PPS. See PASSENGER PRESENCE SYSTEM (PPS)  under REMOVAL & INSTALLATION. Go to next step.
  7. Reconnect all SIR and PPS components. Verify all components and connectors are installed correctly. Using scan tool, clear all SIR and PPS DTC's. Rezero PPS. See PASSENGER PRESENCE SYSTEM REZEROING PROCEDURE  under DIAGNOSTICS. Road test vehicle. If DTC resets, go to next step. If DTC does not reset, system is okay.
  8. Replace SDM. See SENSING & DIAGNOSTIC MODULE (SDM)  under REMOVAL & INSTALLATION. Go to next step.
  9. Reconnect all SIR and PPS components. Verify all components and connectors are installed correctly. Using scan tool, clear all SIR and PPS DTC's. Rezero PPS. See PASSENGER PRESENCE SYSTEM REZEROING PROCEDURE  under DIAGNOSTICS. Road test vehicle. If DTC resets, go to step  2. If DTC does not reset, system is normal.
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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.