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HOMESERVICE MANUALSCHEVROLET2003TRAILBLAZER 4.2 S, 4WDREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 1345 (ENGINE CONTROL SYSTEM (TROUBLESHOOTING & DIAGNOSIS) -- 1.8L (LNK))TROUBLESHOOTINGSERVICE BAY TESTCHECK MODE
2003 Chevrolet TrailBlazer 4.2 S, 4WD

Check Mode

2003 Chevrolet TrailBlazer 4.2 S, 4WDSECTION Check Mode
WARNING: This page is about a different car, the 2004 Pontiac Vibe. However, it is still accessible from the selected car via links, so may be relevant.

Check Mode can be used to increase the ability of the powertrain control module (PCM) to detect engine control system malfunctions. The PCM can be requested to operate in Check Mode by using the Output Controls feature of the scan tool. While in Check Mode operation the PCM will turn ON the malfunction indicator lamp (MIL) and record Freeze Frame data even on the first failure of a B type DTC. Not all engine control system diagnostics will be enhanced by Check Mode operation. The Check Mode service bay test can be performed while driving the vehicle in order to duplicate the customer concern. Those diagnostics most commonly known to benefit from Check Mode operation will be specified in the diagnostic procedure.

In order to activate the enhanced diagnostics of Check Mode operation, perform the following procedure:

IMPORTANT: DO NOT turn OFF the ignition anytime during or after the operation of the vehicle in Check Mode. Observe and capture all Check Mode operation DTC and Freeze Frame information on the scan tool before turning OFF the ignition. Any DTC or Freeze Frame information that occurred during Check Mode operation will be cleared by the PCM when the ignition is turned OFF.
  1. Capture or save any DTC or Freeze Frame information on the scan tool before entering Check Mode operation. All DTC and Freeze Frame information will be cleared by the PCM when Check Mode is entered.
  2. Turn ON the ignition, with the engine OFF.
  3. Enter Check Mode operation with the scan tool from the Special Functions selection. Verify that the MIL is flashing which indicates that the Check mode request was received and accepted.
  4. Return to the Data List selection on the scan tool.
  5. DO NOT turn OFF the ignition after requesting Check Mode operation with a scan tool. The PCM will return to Normal Mode operation when the ignition is cycled from ON to OFF to ON.
  6. Start the engine.
  7. Operate the vehicle within the conditions under which the original concern was noted or within the Freeze Frame conditions that set the DTC.
  8. The Diagnostic Mode parameter in the scan tool data list can be viewed at anytime in order to verify that the vehicle is still operating in Check Mode.
  9. If the MIL illuminates while in Check Mode, observe and capture all DTC and Freeze Frame information with the scan tool.
  10. Check Mode operation can be terminated by cycling the ignition switch, or commanding Normal Mode with the scan tool.
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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.