Theory Of Operation

The purpose of the diagnostic is to detect a stuck position of one of the two parking lock valves in the hydraulic control unit. The purpose of the two parking lock valves is to cut or provide the oil supply in the hydraulic control unit to the parking lock. The parking lock can only be disengaged if both parking lock valves are supplying hydraulic pressure. When the parking lock is engaged during engine off and one of the parking lock valves is stuck in the supply position, a restart of the engine can only cause an unwanted disengaging of the parking lock if a separate failure occurs with the second parking lock valve. This monitor is a once-per-trip diagnostic that only occurs after an engine start (not during remote start).