Theory Of Operation

The purpose of the diagnostic is to check if the output speed sensor signal is rational by monitoring for either a missing or invalid speed sensor signal. The output speed sensor is a Hall Effect sensor with an output range that alternates between normal high and normal low voltages as the output shaft tone wheel rotates. The three rationality checks performed by the TCM include a turbine speed comparison check, a maximum negative gradient check, and a wheel speed comparison check.

Turbine Speed Comparison:  If number of output speed sensor pulses is equal to zero while the number of turbine speed sensor pulses is greater than or equal to a threshold for a calibrated number of continuous occurrences, a fault code will be set.