Theory Of Operation

The purpose of the diagnostic is to detect an unwanted power flow in the transmission. A rationality check of the ratio of input speed to engine speed is done while no power flow is requested. When the transmission is in Park or Neutral, the input shaft RPM (indicated by the Input Speed Sensor) should be close to the same as the engine RPM received over the Bus. When the transmission is in a driven gear with the engine running and vehicle is not moving, the input shaft RPM should be zero RPM. This DTC sets indicates that the transmission input RPM is below a minimum threshold compared to engine RPM when the transmission is in Park or Neutral.