Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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HOMESERVICE MANUALSISUZU2006ASCENDER S, 4.2 S, 4WDREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 236 (ENGINE CONTROL SYSTEM & FUEL SYSTEM - 4.2L - DTC P0135 TO DTC P0420)DTC P0418CIRCUIT/SYSTEM TESTING
2006 Isuzu Ascender S, 4.2 S, 4WD
Circuit/System Testing
2006 Isuzu Ascender S, 4.2 S, 4WDSECTION Circuit/System Testing
WARNING: This page is about a different car, the 2007 Isuzu Ascender, 2007 GMC Envoy, 2007 Chevrolet TrailBlazer, and 2007 Buick Rainier. However, it is still accessible from the selected car via links, so may be relevant.
- Ignition OFF, disconnect the pump relay.
- Ignition ON, connect a test lamp between the positive terminal at the battery and the relay control circuit terminal.
- 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.
- 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.
- 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.
- 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.
- If all circuits and the control module test normal, test or replace the relay.
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When to See a Mechanic
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.