BMW Fault Code P0456 – Evaporative Emissions System Leak

A BMW fault code P0456 means that there is a leak somewhere in your fuel system that is allowing fuel vapors to escape into the atmosphere. Your BMW is equipped with what is called an evaporative emissions system, also known as EVAP. EVAP is an important part of your BMW's emissions system - through a network of sensors, hoses, and valves the EVAP system captures fuel fumes and stores them where they can be sent back to the engine for combustion. The pressure in the EVAP system is monitored regularly by your BMW's engine computer known as the DME. If the pressure in the EVAP system drops there is an air leak allowing fumes to escape, triggering the DME to create a fault code P0456.

As previously discussed, a BMW fault code P0456 is caused by a leak somewhere in your BMW's fuel system allowing fumes to escape. The most likely culprit is a faulty fuel filler cap or a filler cap not properly inserted. Other causes can include cracked or loose fuel ventilation lines, a air leak in the fuel tank (usually around the fuel pumps), a damaged charcoal filter, or a worn-out fuel vent valve.

Unfortunately, there are no major symptoms associated with an EVAP leak other than a pesky "service engine light" in the instrument cluster and an emissions warning on the iDrive screen.

1. The first thing you should do before diving into an extensive diagnosis of the source of BMW fault code P0456 is check the gas cap. Make sure it is tightly screwed into the fuel filler hose. If the cap is tightly installed and you are still getting the error code, we suggest just replacing it before proceeding. Gas caps are cheap...and since the next step is more involved, it's money well spent just to install a new one.
2. If step 1 does not cure the issue, then you will have to smoke test the EVAP system to find out where the leak is. This requires the use of a diagnostic smoke machine usually attached to the tank vent valve in the engine compartment.
3. There also may be an issue with the fuel tank vent (breather) valve in the engine compartment. The fuel tank vent valve allows gas fumes from the EVAP system to enter the engine so they can be combusted.