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Home >> Cadillac >> 2010 >> Escalade EXT >> Repair and Diagnosis (Single Page) >> Engine Performance >> System >> Engine Control System & Fuel System - 5.3L, 6.0L, 6.2L - DTC P1255 To DTC P3449 >> DTC P2636 >> Circuit/System Testing
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Circuit/System Testing

  1. Ignition OFF, disconnect the fuel pump relay.
  2. Ignition ON, verify that a test lamp illuminates between the ground circuit terminal 85 and B+.
    • If the test lamp does not illuminate, test the ground circuit for a short to voltage or an open/high resistance.
  3. Verify that a test lamp does not illuminate between the ground circuit terminal 85 and the control circuit terminal 86.
    • If the test lamp illuminates, test the control circuit for a short to voltage. If the circuit tests normal, replace the ECM.
  4. Remove the test lamp.
  5. Command the fuel pump relay ON with a scan tool. Verify the scan tool fuel pump relay Ckt. Short Grnd Test Status parameter is OK.
    • If not the specified value, test the fuel pump relay control circuit for a short to ground. If the circuit tests normal, replace the ECM.
  6. Install a 3A fused jumper wire between the fuel pump relay control circuit terminal 86 and the ground circuit terminal 85. Command the fuel pump ON with a scan tool. Verify the scan tool fuel pump relay Ckt. Short Grnd Test Status parameter is Fault.
    • If not the specified value, test the fuel pump relay control circuit for an open/high resistance. If the circuit tests normal, replace the ECM.
  7. Inspect the fuel pump fuse.
    • If the fuel pump fuse is open, test for the following conditions:
      • A short to ground in the relay switch B+ circuit
      • A short to ground in the supply voltage circuit of the fuel pump
    • If the above circuits test normal, replace the fuel tank module.
  8. Verify that a test light illuminates between the B+ circuit and ground.
    • If the test lamp does not illuminate, test the B+ circuit for an open/high resistance.
  9. Connect a 15A fused jumper wire between the B+ circuit and the supply voltage circuit of the fuel pump. Verify the fuel pump is activated.
    • If the fuel pump does not activate, test for the following conditions:
      • An open/high resistance in the supply voltage circuit of the fuel pump
      • An open/high resistance in the ground circuit of the fuel pump
    • If the above circuits test normal, replace the fuel tank module.
  10. If all circuits test normal, test or replace the fuel pump relay.
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