Mercedes-Benz SL63 AMG Air Injection System Air Bypass Valve Replacement Cost

Air injection systems are emissions components that send clean air to the exhaust system which allows the catalytic converter to completely burn fuel before it is released through the exhaust pipe. Modern vehicles may still use vacuum operated air pumps, but that is much less common that computer controlled actuation. In these systems, the engine control module (ECM) will determine when the pump should not send clear air to the exhaust system and open the air bypass valve to allow clean air into the engine instead.

The air bypass valve is installed on the secondary air pump, or inside a line from the secondary air pump to the intake manifold. When the valve is opened, the air pressure generated by the air pump will be sent into the engine instead of the exhaust. Once the ECM closes the valve, the air pressure from the secondary air injection pump will be sent to the exhaust and catalyze the fuel at the catalytic converter.

If the air injection system air bypass valve is no longer able to open or close, or stays open at all times, the fuel to air ratio for the vehicle will suffer as will engine performance. If the valve sticks closed, the pump will only be capable of pumping air into the exhaust. This will cause the oxygen sensors to sense a lean condition and the check engine light will appear. Also, the ECM will detect insufficient flow of air to the engine which may result in storage of OBD-II trouble codes related to the mass airflow sensor or manifold absolute pressure sensor. On the other hand, a valve that is stuck open will result in the oxygen sensors reporting rich running conditions, and the mass air flow or manifold absolute pressure sensor reporting errors. The vehicle will likely run roughly, can hesitate on acceleration, and misfires may be present.