No Start after Refueling and Popping Noise from Trunk on Audi S6

Popping sounds from the rear of the vehicle may be heard moments after starting the engine, or when slowing to a stop. This noise is from the leak detection pump filling the fuel tank with air, and releasing to retest the system when it finds a fault. The sequence of faults identifying this issue are as follows:

• Succession of loud pops from rear of vehicle
• Pops go away, and fuel economy decreases
• Check engine light illuminates
• OBD trouble code P2404 and/or P0441is stored
• Engine will not start after refueling (must crank for over 30 seconds)
• Vibration when slowing to a stop

The cause is a valve which is mounted on the front of the intake manifold, commonly called the N80 valve, or EVAP system purge valve. The valve is designed to open under specific circumstances, but a worn valve will remain open at all times, preventing the pressurization of the fuel tank.

Correction of the issue is to replace the N80 valve with the latest revision.