Theory Of Operation

The purpose of the diagnostic is to detect rationality failures of the input speed sensor signal. This diagnostic checks if the input speed sensor signal is within the calculated tolerance bands.

The upper threshold of the first tolerance band is the greater value of either the engine speed or calculated input speed, plus a calibrated offset. The calculated input speed is based upon the output speed signal multiplied by the gear ratio factor. This factor corresponds to either the target gear or current gear depending on which gear provides the greater ratio.

The lower threshold of the first tolerance band is the lesser value of either the engine speed or calculated input speed, minus a calibrated offset. The calculated input speed is based upon the output speed signal multiplied by the gear ratio factor. This factor corresponds to either the target gear or current gear depending on which gear provides the lesser ratio.

The thresholds of the second tolerance bands are calculated using the same method described above. In place of the output speed signal, the wheel speed signal via CAN is used for the calculation.