The customer reported the vehicle went into limp mode.

The vehicle had fault code P0513 (Incorrect Immobilizer Key) stored. Diagnosis identified a faulty throttle body and ECM. The throttle body was replaced and a second-hand ECM fitted. After programming the ECM via the AC Delco system, the throttle body operated correctly, but the engine would not start and displayed “engine immobilised refer to owners manual.” Fault code P0513 returned, and the security light extinguished as expected with the key turned on.