Theory Of Operation

This diagnostic checks for the number of unexpected mechanical disengagements of any forward and reverse engaged gears occurring during a trip without receiving a control signal to disengage from the Transmission Controller Module (TCM). The total number of gear engagement control actions and the total number of unexpected gear disengagements during a trip are accumulated in the internal memory of the TCM. The two separate registers in the internal memory which contain these counters are cleared after every trip. When the accumulated number of the unexpected gear disengagements during a trip is greater than a threshold, this diagnostic will be considered failing.