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 MANUALSCHEVROLET2008CHEVY EXPRESS G2500, VAN CARGO, 6.6 6REPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 1975 (DATA COMMUNICATION SYSTEM)DIAGNOSTIC INFORMATION AND PROCEDURESDTC U1863CIRCUIT/SYSTEM TESTING
2008 Chevrolet Chevy Express G2500, Van Cargo, 6.6 6
Circuit/System Testing
2008 Chevrolet Chevy Express G2500, Van Cargo, 6.6 6SECTION Circuit/System Testing
WARNING: This page is about a different car, the 2009 Saturn Vue. However, it is still accessible from the selected car via links, so may be relevant.
- Using the DTC Descriptor and Diagnostic Aids above, determine the module that is not communicating that should be tested.
- Ignition OFF, disconnect the harness connector at 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, test or replace the 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, test or replace the module.
- Test for less than 10 ohms between the module ground circuits and ground.
- If greater than the specified range, test the ground circuit for open/high resistance.
- Test for less than 1 ohm on the high speed GMLAN serial data circuits between the non-communicating module and the module that displays the DTC.
- If greater than the specified range, test the serial data circuits for an open/high resistance.
- If all circuits test normal, test or 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.