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Home >> Isuzu >> 2007 >> Ascender 4WD >> Repair and Diagnosis >> Engine Performance >> System >> Engine Control System & Fuel System - 4.2L - DTC P0135 To DTC P0420 >> DTC P0418 >> Circuit/System Testing
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Circuit/System Testing

  1. Ignition OFF, disconnect the pump relay.
  2. Ignition ON, connect a test lamp between the positive terminal at the battery and the relay control circuit terminal.
  3. Command the 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 control circuit for a short to ground. If the circuit tests normal, replace the control module.
    • If the test lamp is always OFF, test the relay control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the control module.
  4. Connect a 30A fused jumper wire between the positive voltage terminal at the battery and the pump voltage supply circuit terminal and verify pump activation.
    • If the pump does not activate, test the pump voltage supply circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the pump.
  5. Ignition ON, connect a 30A fused jumper wire between the relay switch voltage supply circuit terminal and the pump voltage supply circuit terminal and verify pump activation.
    • If the pump does not activate, test the relay switch voltage supply circuit for a short to ground or an open/high resistance. If the circuit tests normal and its fuse is open or test all connected components and replace as necessary.
  6. Ignition ON, verify that a test lamp illuminates between the relay coil voltage supply circuit terminal and ground.
    • If the test lamp does not illuminate, test the affected relay coil voltage supply circuit for a short to ground or an open/high resistance. If the circuit tests normal and its fuse is open or test all connected components and replace as necessary.
  7. If all circuits and the control module test normal, test or replace the relay.
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