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 G3500, VAN PASSENGER EXTENDEDREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 405 (DATA COMMUNICATION SYSTEM)DIAGNOSTIC INFORMATION AND PROCEDURESDTC U1825CIRCUIT/SYSTEM TESTING
2008 Chevrolet Chevy Express G3500, Van Passenger Extended
Circuit/System Testing
2008 Chevrolet Chevy Express G3500, Van Passenger ExtendedSECTION Circuit/System Testing
WARNING: This page is about a different car, the 2009 Cadillac STS. However, it is still accessible from the selected car via links, so may be relevant.
- With a scan tool, verify DTC U0100-U0299 or U2105-U2199 is not set as current.
- If DTC is set, refer to DTC U0100-U0299 or DTC U2105-U2199
- Ignition OFF, test for less then 5 Ohms of resistance between the applicable modules ground circuit and ground.
- If greater then the specified range, test the circuit for an open/high resistance.
- Ignition OFF, disconnect the applicable modules harness connector.
- Ignition ON, verify a test lamp illuminates between the following circuits of the applicable module and ground.
- The battery positive voltage input circuits.
- The battery positive voltage output circuits.
- The ignition voltage input circuits.
- The ignition voltage output circuits.
- The switched battery positive voltage supply circuits.
- If the test lamp does not illuminate, test the circuit for an open/high resistance. If the circuit fuse is open, test the circuit for a short to ground. If the circuit tests normal, replace the applicable control module.
- Ignition OFF, test for less then 5 Ohms of resistance between the non-communicating modules GMLAN serial data circuits and the module reporting DTC U1825.
- If greater then the specified range, test the circuit for and open/high resistance.
- If all circuits test normal, replace the applicable control module.
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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.