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.
Diagnostic Aids
Diagnostic procedure used for DTC U1500 in OnStar® systems with single module generations of OnStar® differ greatly from previous generations with two modules. Older generation system denoted a failure of three wire serial data bus between modules by setting a U1500. Single module OnStar® systems use DTC U1500 to indicate internal module failure. Determination of whether a one or two module generation of OnStar® is used should be confirmed. DTC U1500 may be stored as a history DTC without affecting operation of VCIM. If stored only as a history DTC and not retrieved as a current DTC, do not replace VCIM. If DTC U1500 is retrieved as both a current and history DTC, replace VCIM.
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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.