Theory Of Operation

The purpose of the diagnostic is to check if the transfer case status signal received via CAN is valid. The transfer case status signal is sent by the Body Control Module (BCM) for vehicles equipped with a manual transfer case, or by the Drive Train Control Module (DTCM) for vehicles equipped with an electronic transfer case. The transfer case status signal consists of 4WD high, 4WD low, 2WD and neutral. The TCM checks the transfer case status for a "Signal Not Available" (SNA) or an invalid transfer case status signal. If the transfer case ratio indicated by the CAN transfer case status, and the transfer case ratio calculated in the TCM, do not match for a calibrated amount of time, a DTC will be set.