The Engine Control Module (ECM) and Transmission Control Module (TCM) use several sensors for the right operation of the engine and transmission and monitor these components. To determine the shift patterns, the TCM monitors the shift position switch and the park/neutral switch. The signal from both switches is highly dependent on the position of the shift lever. This signal is used to enable or disable engine start and cruise control.
The ECM continuously monitors the parking switch and compares its signal with the set values. In case it is out of the expected parameters, the DTC P0850 OBD2 will be set.