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HOMESERVICE MANUALSPONTIAC2008GRAND PRIX BASEREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 450 (ENGINE CONTROL SYSTEM & FUEL SYSTEM - 5.3L - DTC P0420 TO DTC P3449)DTC P1682CIRCUIT/SYSTEM TESTING
2008 Pontiac Grand Prix Base

Circuit/System Testing

2008 Pontiac Grand Prix BaseSECTION Circuit/System Testing
WARNING: This page is about a different car, the 2008 Buick LaCrosse and 2008 Buick Allure. However, it is still accessible from the selected car via links, so may be relevant.
IMPORTANT: You must perform the Circuit/System Verification before proceeding with Circuit/System Testing.

Testing the Ignition 1 Signal Circuit

    IMPORTANT: A resistance of 5 ohms or greater in the circuit will cause the DTC to set.
  1. Ignition ON, verify that B+ is available to both test points of the fuse from the powertrain relay to the ECM.
    • If B+ is only available on one test point of the fuse, test the ignition 1 voltage circuit from the fuse to the ECM for a short to ground. If the circuit tests normal, replace the ECM.
    • If B+ is not available on either test point of the fuse, replace the underhood fuse block.
  2. Ignition OFF, disconnect the ECM C1 connector.
  3. Ignition ON, verify that B+ is available at C1-19.
    • If B+ is not available, test the ignition 1 voltage circuit for an open/high resistance condition. If the circuit tests normal, replace the ECM.
  4. If all circuits test normal, replace the ECM.

Testing the EC Ignition Relay Feedback Circuit

    IMPORTANT: A resistance of 5 ohms or greater in the circuit will cause the DTC to set.
  1. Ignition OFF, remove the powertrain relay from the underhood fuse block.
  2. Ignition ON, connect a 3A fused jumper wire from B+ to the powertrain ignition 1 voltage circuit terminal. Verify that the EC Ignition Relay Feedback parameter displays B+ on the scan tool.
    • If the scan tool parameter is less than the specified value, test the ignition 1 voltage circuit for an open/high resistance or short to ground. If the circuit tests normal, replace the ECM.
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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.