What is AEM bypass valve?

 

The AEM (Advanced Engine Management Inc. ) bypass valve is used to keep water out of your engine in case your air filter gets submerged in water during a flood. This is used mostly with cold air intake systems CAI.

 

It works by incorporating several spring loaded flaps that can open and allow air to 'bypass' the filter. This happens when enough water is drawn into the filter to block the intake of air, causing the pressure in the intake to rise enough to force the springs on the bypass valves to open. AEM recalled some of their early bypass valves because the springs holding the flaps broke and allowed small metal pieces to be drawn through the intake into the engine. The bypass valve is really only necessary if you have a cold air intake located low enough to encounter a significant amount of water. Rain should not produce enough water to cause a problem by itself, you would need the air filter to encounter enough water to fill a section of the intake so that air couldn't get by, and high enough engine RPM to produce enough vacuum in the intake to pull the water into the engine.