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 following rationality checks are performed by the TCM:

• 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.
• Maximum Negative Gradient:  If the output speed sensor signal decelerates at a rate greater than a threshold, a fault code will be set.
• 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 fault code 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 fault code will be set.