Ford P0478 OBD-II Trouble Code Definition: P0478 Exhaust Pressure Control Valve High P0478 Ford OBD-II Trouble CodeDescription: OBD Trouble Code P0478 Exhaust Pressure Control Valve High What does the code mean? OBD-ii Code P0478 definition: Exhaust Back Pressure Regulator – Is a variable position valve that controls exhaust back pressure during cold ambient temperatures to increase […]