Theory Of Operation

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This diagnostic checks the validity, availability and rationality of the engine speed signal which is sent by the Powertrain Control Module (PCM) via a CAN message. The diagnostic checks the validity by performing a CRC and message counter check to be sure the engine speed signal is continuously updated by the PCM and that it has a valid value. The diagnostic also checks the availability by checking the received value is not equal to the Signal Not Available (SNA) default value. Then the diagnostic checks the rationality by comparing the received engine speed to the odd or even clutch speed and to the odd or even input shaft speed. The clutch speed is measured directly from the clutch speed sensor and the input shaft speed is calculated based upon the driveline speed multiplied by the actual gear ratio. Any reference to odd or even is directly related to the actual odd or even gear engaged.