I have a 2012 C300 and the check engine light comes on every few days. My code reader says p0496, evaporative emission system high purge flow. Any ideas what could be causing it?

I have checked and rechecked the gas cap and the code comes back. I did find one thread for this code and all of the folks who replaced their gas cap had the code return so looking for other solutions

I pulled the evap purge valve out and tested it with a hand vacuum pump. At first, when I applied 25 bar of vacuum, it would hold but when I applied 15-17 bar of vacuum (which is what the engine vacuuum would be), it dropped to zero in about 10 seconds. So ordered a new valve from eEuroparts and will report back once it is installed.

I installed the new purge valve yesterday and will now give it a week of drive cycles to see if the problem is cured. Will report back.

The purge valve did it. Problem solved