Diagnostic Aids
WARNING: This page is about a different car, the 2002 Oldsmobile Aurora. However, it is still accessible from the selected car via links, so may be relevant.
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.