From Ed (efair) have you filled up the tank recently? check the fuel cap
It sounds like the code was cleared but the condition that gave rise to the code wasn't. I fixed this code on my other (non-MB 1997) car. Here's some background info I discovered: The charcoal canister stores fumes off the top of your fuel tank and must be periodically "purged" of these stored fumes (or else the fumes accumulate in the canister to the point of saturation). Generally, to purge the canister, air is drawn into the engine through the canister and the stored fumes are simply sucked into the engine and burned. The canister is purged under computer control by use of an electrically operated valve, and during the purge cycle, the computer "watches" for key indications that the purge is actually working... the thought being if it's not working, your fumes are likely polluting the air. Your car's running fine, just polluting the air. The computer can "watch" this process in many ways -- O2 sensor changes due to fuel-laden air being drawn in, or by measuring the vacuum being drawn. Frequently the air is drawn through the fuel tank and the vacuum in the gas tank is what the computer "watches". That's why a bad fuel cap will often trigger this code -- the computer doesn't see the desired vacuum.
The purge valve in my other car was in-line between the canister and the intake manifold, and is supposed to be normally closed. I removed the electrical and vacuum lines and tested it with a hand-held vaccum pump -- I confirmed it was not truly "closed" when it was disconnected; I replaced the valve and cleared the codes, and it never came back.
