I had a check engine light come on few days ago on my 2000 C230 and then couple days later the low fuel light started flashing. I had a friend test with the computer and its in the fuel pressurization system. He cleared the light and it came back on again this morning. I know the fuel cap was replaced at some point by the previous owner but I'm not sure how long ago. A shop told me they replaced a couple fuel sending units on this model recently for the same problem. Any one have any experience in this area? Trying to go the lowest cost route. Fuel sending unit is $112 and $77 labor or I could try another fuel cap for $15.00.

 

No doubt, the first thing to buy is a new gas cap. I had the same symptons (forget the trouble code, but think it was 455?)
I purchased two aftermarket gas caps and still had the problem. I began to think I was going to have to spend lots of money. Then I bought an OEM cap from the dealer. Problem solved. (Your gas cap should turn a quarter turn or more after it engages.)
good luck.