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HOMESERVICE MANUALSCHEVROLET2003TRAILBLAZER 4.2 S, 4WDREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 1799 (IMMOBILIZER SYSTEM)DIAGNOSTIC INFORMATION AND PROCEDURESDTC P1631TEST DESCRIPTION
2003 Chevrolet TrailBlazer 4.2 S, 4WD

Test Description

2003 Chevrolet TrailBlazer 4.2 S, 4WDSECTION Test Description
WARNING: This page is about a different car, the 2007 Saturn Vue. However, it is still accessible from the selected car via links, so may be relevant.

The numbers below refer to the step numbers on the diagnostic table.

  1. 2:  This DTC may set as a result of other Passlock™ System problems. Diagnose any BCM DTCs prior to continuing with this diagnostic.
  2. 3:  A DTC B3031 may set in the BCM during the Password Learn Procedure.
DTC P1631

Step Action Yes No
Schematic Reference: Data Communication Schematics
1 Did you perform the Diagnostic System Check - Vehicle? Go to Step 2  Go to Diagnostic System Check - Vehicle
2 
IMPORTANT: You must diagnose the Bxxxx codes prior to diagnosing any Pxxxx code.
  1. Install a scan tool.
  2. Momentarily rotate the ignition switch to CRANK. Do not start the vehicle.
  3. Release the ignition switch to ON.
  4. Select the powertrain control module display DTCs function on the scan tool.
Does the scan tool display DTC P1631 as a current DTC?		 Go to Step 3  Go to Testing for Intermittent Conditions and Poor Connections
3  Perform the Passlock™ Programming procedure. Refer to Programming Immobilizer System Components .
Did the powertrain control module (PCM) successfully learn the password?		 Go to Step 4  Go to Diagnostic System Check - Vehicle
4
IMPORTANT: Before clearing DTCs, monitor all DTC status parameters and note any additional DTCs.
  1. Clear the PCM DTCs.
  2. Turn OFF the ignition for 30 seconds.
  3. Attempt to start the engine.
Does the engine start and operate normally?		 System OK Go to Step 2 
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.