This can occur because the immobilizer module (SKIM/SKREEM) was not present during bench programming. Without the module connected, the PCM cannot complete the SKIM handshake, which causes code P0633 to be stored. If your vehicle starts, runs normally, and the check engine light is not on, P0633 is not a performance issue and is not harmful. It simply indicates that the immobilizer pairing was not finalized during programming. To fully clear the code, a technician can perform a SKIM initialization by entering your 4-digit security PIN (available from the dealer or third-party service) using a compatible scan tool.
