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HOMESERVICE MANUALSCHEVROLET2008CHEVY EXPRESS G3500, VAN PASSENGER EXTENDEDREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 249 (ENGINE CONTROLS AND FUEL - 4.4L - DTC P0650 TO DTC P2544)DTC P0685 OR P0690CIRCUIT/SYSTEM TESTING
2008 Chevrolet Chevy Express G3500, Van Passenger Extended

Circuit/System Testing

2008 Chevrolet Chevy Express G3500, Van Passenger ExtendedSECTION Circuit/System Testing
WARNING: This page is about a different car, the 2008 Cadillac STS. However, it is still accessible from the selected car via links, so may be relevant.
    IMPORTANT: You must perform the Circuit/System Verification first.
  1. Ignition OFF, disconnect the powertrain relay.
  2. Ignition ON, verify that a test lamp illuminates between the powertrain relay coil B+, and ground.
    • If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance. If the circuit tests normal, test or replace the battery positive cable to the underhood fuse block.
  3. Ignition OFF, verify that a test lamp does not illuminate between the powertrain relay coil B+ circuit and the control circuit.
    • If the test lamp illuminates, test the control circuit for a short to ground. If the circuit tests normal, replace the ECM.
  4. Remove the test lamp.
  5. Command the engine controls ignition relay ON, with a scan tool. Verify with a scan tool that the EC Ign. Relay CKT. Short Volts Test Status parameter is OK.
    • If not the specified value, test the control circuit for a short to voltage. If the circuit tests normal, replace the ECM.
  6. Test the coil side of the powertrain relay for 65-110 ohms.
    • If not within the specified value, replace the relay.
  7. Ignition OFF, disconnect the ECM X1 connector.
  8. Test the powertrain relay control circuit for an open/high resistance.
    • If the circuit tests normal, replace the ECM.
  9. Verify that a test lamp does not illuminate between the relay ignition 1 voltage circuit and ground.
    • If the test lamp illuminates, test the relay ignition 1 voltage circuit for a short to voltage. If the circuit tests normal, replace the ECM.
  10. Verify that a test lamp illuminates between the relay switch B+ and ground.
    • If the test lamp does not illuminate, test the relay switch B+ circuit for a short to ground, or an open/high resistance. If the circuits test normal, and the fuse for the ignition 1 voltage circuit is open, test the ignition 1 voltage circuit to the ECM for a short to ground. If the circuit tests normal, replace the ECM.
  11. Connect a 20A fused jumper wire between the relay switch B+ and the relay ignition 1 voltage circuit.
  12. Ignition ON, engine OFF, monitor the EC Ignition Relay Feedback parameter with a scan tool. The parameter should display B+.
    • If the parameter does not display B+, test the ignition 1 voltage circuit for an open/high resistance. If the circuit tests normal, replace the ECM.
  13. If all circuits test normal, replace the relay.
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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.