A leak detection pump in an automobile identifies fuel system leaks that may affect vehicle performance and harm the environment. It does so by pumping air into the fuel tank and charcoal canister so that the engine control module (ECM) can measure the system's pressure decay. Leaks are the most common cause of "check engine" light activations.
A leak detection pump is made up of a vacuum line from the vehicle fuel system, a pressure-sensitive diaphragm and a solenoid that converts information from the diaphragm to electrical data, which can be interpreted by the ECM to identify any leak presence and magnitude. A leak detection pump doesn't specify the location of any leak, only its existence and severity. If a leak is detected, additional investigation is required to identify the location.
A vehicle's evaporative control system (EVAP) is comprised of the fuel tank, hoses, charcoal canister, and related solenoids and sensors. The introduction of regulations in 1996 made it mandatory for the EVAP system of every vehicle to be checked for leaks automatically. In subsequent years, the regulations became even stricter, mandating leak detection abilities of two one-hundredths of an inch. These higher standards led many manufacturers to install leak detection pumps on all new vehicles.