I purchased a '95 E320 with 81,xxx miles on it. It ran and runs great. Problem is the check engine light came on recently while in Hilton Head, SC. I stopped by at the dealer in HH and asked could they scan the code. The lady told me to just check the gas cap to insure that it was tight which it was. I had put a can of Outlaw fuel injection cleaner in it (I have done this to all of my cars at around 80k miles) and when the tank got down to around 1/4 tank I filled it up again with Amoco 93 octane then drove it for 30 miles. The light did not come on while driving. It came on when I started up the next day. I unhooked the battery for 10 seconds and the check engine light went off and then came back on after about 25 miles of driving. Do I need to replace the O2 sensor? Where is it located - do I get to it underneath the car or under the hood? Is there another place to reset the check engine light? Otherwise it runs great and I got 25.9 mpg on this last tank of gas. Any thoughts/ideas.