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 414 (ENGINE CONTROL SYSTEM & FUEL SYSTEM - 4.2L - DTC P0366 TO DTC P2444)DTC P0412 OR 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 2008 Isuzu Ascender, 2008 GMC Envoy, and 2008 Chevrolet TrailBlazer. However, it is still accessible from the selected car via links, so may be relevant.
- Ignition OFF, disconnect the affected relay.
- Ignition ON, connect a test lamp between the positive terminal at the battery and the relay control circuit terminal 85.
- 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 ECM.
- 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 ECM.
- Connect an appropriately fused jumper wire between the positive voltage terminal at the battery and the load voltage supply circuit terminal 87 and verify load activation.
- If the load does not activate, test the load voltage supply circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the load.
- Ignition ON, connect an appropriately fused jumper wire between the relay switch voltage supply circuit terminal 30 and the load voltage supply circuit terminal 87 and verify load activation.
- If the load 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, test all components connected to the fuse and replace as necessary.
- Ignition ON, verify that a test lamp illuminates between the relay coil voltage supply circuit terminal 86 and ground.
- If the test lamp does not illuminate, test the relay coil voltage supply circuit for a short to ground or an open/high resistance.
- If all circuits and the ECM test normal, test or replace the affected 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.