Clearing the CEL....? Why did the ECU not reset?

(I have a 96 Oldsmobile Cutlass Ciera)

My CEL had come on a few days ago and I found the error was the map sensor. I disconnected my battery and then installed the new sensor. Once completed, after 30 minutes had elapsed, I reconnected the negative battery cable. For some reason, the CEL is still on. I thought the ECU would have reset after 30 minutes. Any other ideas on what to do? Thanks.

If I am wrong on this someone correct me.I understand some (or all) ODBII systems won't clear unless done with a scanner. Unhooking battery won't do it. Perhaps yours falls into that group? Only other thing I could think is that perhaps there is another sensor causing the problem or ECM could be going bad... It is not uncommon for one sensor to cause a setting elsewhere, and I had a Corsica that kept telling me the digital EGR was bad, even after replaced. ECM was bad.

well i just read about this in class and you could be right bout the ecm or another sensor but i know it says that it may take from 1 to several hours for a code to be erased when u disconnect the battery. iit varies depending on car or code so 30 minutes would not be sufficient i hope that helps a little.

Thanks. The code actually cleared the morning after. Fortunately, the CEL hasn't come back on since!