What is Leak Detection Pump and How it Works


Evaporative emissions control or EVAP systems are a part of vehicle emission control since the 70s. This system prevents fuel tank vapors from venting into the atmosphere. It collects and stores these vapors and, at the correct time, and moves them to the intake manifold for combustion. EVAP systems have changed over the years, evolving from simple fuel tank vacuum operated types to sealed, OBD2 monitored, and ECM controlled systems. Fuel filler caps are non-venting and have a positive and negative pressure relief valve built-in.

What is Leak Detection Pump used for?

Many newer cars made by BMW, as well as other European and Japanese car manufacturers, use Leak Detection Pump to pressure the EVAP system to perform diagnosis. This system works by pumping pressurized air into the EVAP system to test it for leaks. The pump has a series of one-way valves and a vent valve, a sensor at the top, vacuum solenoid and a spring-loaded diaphragm. It uses an engine vacuum to move the diaphragm up and down. This motion, controlled by the solenoid, pressurizes the EVAP system. When the pump reaches a specific amount of pressure, it will stop the up-and-down movement and close the vent valve at the bottom of the pump. This seals the EVAP system, and the ECU starts the monitoring procedure. During this time, the pressure within the system must remain above a preset value. If it passes, the ECU activates the vacuum solenoid placed at the top of the LDP pump and releases the pressure from the EVAP system. When this happens, the diaphragm will also push on the vent valve, allowing fresh air from outside to enter the system.

Have in mind that the pressure inside the EVAP system during the monitoring process is low. Also, the entire pump is calibrated to pump a certain amount of pressure and stay in the up position after reaching that pressure. This system differs from ones used by other manufacturers is that it doesn’t rely on a fuel tank pressure sensor to do the EVAP testing. The ECU looks at a sensor reading as an indicator of pressure, since it knows that the diaphragm will have to stay in the up position when the system is pressurized. Any changes in these readings will mean there is a leak. If the pump cannot reach the preset pressure, the ECM will know according to the severity of the signal that there is an impending large EVAP leak. This is why cars with this system can issue a code such as a large leak detected or a small leak detected. The ECM monitors at the frequency output of the read switch to determine how big the leak is.

Common problems

The pump itself is the most common failure point. Usual causes are diaphragm rupture, inoperable solenoid, or jammed valves. When any of these parts fail, replacing the pump is the only viable option. Still, outside issues, such as broken vacuum lines or poor electrical connections can make this system inoperable.

Application list

2006 BMW 135i , 128i , M3 , 330xi , 330Ci , 325xi , 325i , 325Ci , 335i , 328i , 330i, X3, X5

2007 BMW 135i , 128i , M3 , 330xi , 330Ci , 325xi , 325i , 325Ci , 335i , 328i , 330i, X3, X5

2008 BMW 135i , 128i , M3 , 330xi , 330Ci , 325xi , 325i , 325Ci , 335i , 328i , 330i, X3, X5

2009 BMW 135i , 128i , M3 , 330xi , 330Ci , 325xi , 325i , 325Ci , 335i , 328i , 330i, X3, X5

2010 BMW 135i , 128i , M3 , 330xi , 330Ci , 325xi , 325i , 325Ci , 335i , 328i , 330i, X3, X5

2012 BMW 135i , 128i , M3 , 330xi , 330Ci , 325xi , 325i , 325Ci , 335i , 328i , 330i, X3, X5

2013 BMW 135i , 128i , M3 , 330xi , 330Ci , 325xi , 325i , 325Ci , 335i , 328i , 330i, X3, X5

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