Ford P0543 OBD-II Trouble Code Definition: P0543 Intake Air Heater Incorrect Voltage P0543 Ford OBD-II Trouble CodeDescription: OBD Trouble Code P0543 Intake Air Heater “A” Circuit Open What does the code mean? OBD-ii Code P0543 definition: The engine control module (ECM) uses an intake air heater (IAH) to warm the incoming air for proper cylinder combustion. […]