Theory Of Operation

The purpose of the diagnostic is to detect rationality failures of the Output Speed Sensor signal. This diagnostic checks if the Output Speed Sensor signal is within the calculated tolerance bands.

The upper threshold of the first tolerance band is the calculated output speed plus a calibrated offset. The calculated output speed is based upon the Input Speed Sensor 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 calculated output speed, minus a calibrated offset. The calculated output speed is based upon the Input Speed Sensor 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 Input Speed Sensor signal, the wheel speed signal via the Controller Area Network (CAN) is used for the calculation.

In addition, this diagnostic checks if the rotating direction of the Output Speed Sensor signal corresponds to the actual gear position.