What does it mean?
OBD II fault code P0908 is a generic code that is defined as “Transmission gate select position circuit -intermittent circuit malfunction”, and is set when the PCM (Powertrain Control Module) or TCM (Transmission Control Module), or both modules detect an intermittent failure in the signal from the transmission gate selector position switch.
All automatic transmissions or automated manual transmissions use a position sensor to monitor gear selection, to let the PCM/TCM know which gear the transmission is in. This input data is used to modulate engine power during gearshifts, control torque converter clutch slippage, and to provide a visual indication of the currently selected gear to the driver.
If the signal from the transmission gate selector position switch fails, or fails intermittently, the PCM is unable to control gearshifts effectively, because the control module cannot detect which gear is currently selected. Therefore, when this input data is lost to the PCM, it will set code P0809, and illuminate a warning light. Note that in some cases, the PCM may initiate a failsafe or limp mode both to limit engine power, and to protect the transmission.