The intake boots are an especially common problem on the 2nd gen Mini Cooper S model with turbos. These codes are most typically a result of intake system vacuum leaks, with the most common being cracked or otherwise leaking intake boots. The smoke may also have ultraviolet dye added to make it easier to spot under a UV light. To diagnose the small leaks a smoke machine is used to find the leaks by feeding a mineral oil based smoke into the system under light pressure. The PO442 can be a much harder one to diagnose as it virtually impossible to diagnose visually. The PO455 code is most often caused by a gas cap that was left loose after refueling. The most common fault codes for EVAP leaks are a PO442- Small leak detected, and PO455- Large leak detected. BMW and Mini Cooper are equipped with a Leak Detection Pump (DMTL) for this purpose. The system is designed to detect leaks as small a pin hole. A loose gas cap can cause the light to come on because the system detects that there is pressure loss.

When the computer detects a leak in the system it will trigger the check engine light to come on and warn you. The Evaporative Emission Control System or EVAP system as it is most often called, was designed to prevent gasoline vapors from escaping from the fuel tank and fuel system. How to Check for BMW or MINI Cooper EVAP Leaks

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