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.

• Wheel Speed Comparison:  If the number of output speed sensor pulses is equal to zero while the wheel speed-based calculated output shaft speed is greater than or equal to a calibrated threshold, a DTC will be set.
• Wheel Speed Delta:  If the absolute value of the difference between the measured output shaft speed and the wheel speed-based calculated output shaft speed is greater than or equal to a calibrated threshold, a DTC will be set.