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, 5.3 M, 4WDREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 399 (DATA COMMUNICATION SYSTEM)DIAGNOSTIC INFORMATION & PROCEDURESDTC U1000 & U1255CIRCUIT/SYSTEM TESTING
2006 Isuzu Ascender S, 5.3 M, 4WD
Circuit/System Testing
2006 Isuzu Ascender S, 5.3 M, 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.
- Verify that no DTC within the range of U1001-U1254 exists as current or history in any module.
- If any DTC within the range of U1001-U1254 does exist, refer to Diagnostic Trouble Code (DTC) List - Vehicle .
- Ignition OFF, disconnect the harness connector of the module that is not communicating.
- Ignition ON, verify that a test lamp illuminates between all battery positive voltage circuits and ground.
- If the test lamp does not illuminate, test the circuit for a short to ground or an open/high resistance. If the circuit fuse is open, also test the positive voltage outputs of the module for a short to ground. If the circuits test normal, replace the faulty module.
- Verify that a test lamp illuminates between all ignition voltage circuits and ground.
- If the test lamp does not illuminate, test the circuit for a short to ground or an open/high resistance. If the circuit fuse is open, also test the positive voltage outputs of the module for a short to ground. If the circuits test normal, replace the faulty module.
- Test for less than 1 ohm of resistance between the module ground circuits and ground.
- If greater than 1 ohm, test the ground circuit for open/high resistance.
- Test for less than 1 ohm of resistance in the class 2 serial data circuit(s) between the non-communicating module and the module that displays the DTC.
- If greater than 1 ohm of resistance, test the serial data circuit(s) for open/high resistance.
- If all circuits test normal, replace the module that is not communicating.
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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.