Check engine light after filled up

[zam2000]

Twice in the last two weeks, after I filled up my gas tank, the engine light went on.

Both time, I retight the gas cap, and unplug the battery to reset the CE, and the check engine light went away (until the next fill up).

I think it's the gas cap, anyone experiences similar problem ????.

Again, for both time:

* The gas tank almost go empty before fill up
* Filled up (let it pump til stop).
* Light went on within 10 miles
* Retight the cap & unplug the battery, the light goes away.


Btw, my car is a 98 E320 (W210).