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Home >> GMC >> 2006 >> Sierra 1500 HD, RWD >> Repair and Diagnosis >> External Pages >> Different car >> Section 937 (Engine Controls And Fuel - 4.3L - DTC P0340 To DTC P2138) >> DTC P0685, P0689, or P0690 >> Circuit/System Testing

Circuit/System Testing

WARNING: This page is about a different car, the 2007 GMC Sierra and 2007 Chevrolet Silverado. However, it is still accessible from the selected car via links, so may be relevant.
  1. Ignition OFF, disconnect the powertrain relay.
  2. Ignition ON, verify that a test lamp does not illuminate between the relay coil control circuit and ground.
    • If the test lamp illuminates, test the relay coil control circuit for a short to voltage. If the circuit tests normal, replace the ECM.
  3. Very 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.
  4. Verify that a test lamp illuminates between the relay coil B+ and ground.
    • If the test lamp does not illuminate, test the relay coil B+ circuit for a short to ground or an open/high resistance.
  5. 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.
  6. Connect a test lamp between the relay coil B+ and the relay coil control circuit.
  7. Ignition ON, command the powertrain relay ON and OFF with a scan tool. The test lamp should turn ON and OFF when changing between the commanded states.
    • If the test lamp is always ON, test the relay coil control circuit for a short to ground. If the circuit tests normal, replace the ECM.
    • If the test lamp is always OFF, test the relay coil control circuit for a short to voltage, or an open/high resistance. If the circuit tests normal, replace the ECM.
  8. Connect a 20 amp fused jumper wire between the relay switch B+ and the relay ignition 1 voltage circuit.
  9. 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.
  10. If all circuits test normal, test or replace the replay.
    • 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.
  11. If all circuits test normal, replace the relay.
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