service engine soon light

My 2004 325i just turned 50K miles.......been a very good solid car. I'm nearly age 70 and drive the speed limit; unusual in Ca. Last week I was driving home after filling up at our local Costco. I alternate reg. unleaded with premium and this fill was regular 87 gas. While at a stop light some jerko was in a hurry and pulled into the right lane which was ending after the light; trying to blast off in the lead of all of us waiting for the light change.
I hammered the BMW for the first time in perhaps a year and ended up ahead of the jercko.
About 20 miles later the service engine soonlight came on. I've spend quite abit of time on the net looking into this......The BMW forum as well. Today I noticed ehow had a tip: it involves disconnecting the + battery cable; pull the ECM fuse; wait a few minutes and reconnect the + cable. This is supposed to reset the onboard computer. ??? I suppose it's worth a try.
Will advise if I find it worked. I can't feel any performance difference since the light came on. When the odo reset button is held the service engine light added ECLfault.
I've tried the standard reset for 'inspection' but the mileage and notation continues to come up when I start the car......it goes into? once driving. The dealer said it was likely a BMW reminder to 'flush the cooling system'.
If I have one significant complaint it's these reminders that seem impossible to reset when you do the work yourself.
I"m now shopping for a Autel maxiscan/reset gizmo. Always welcome help. Jonzie

There are over 200 things that will trigger a CEL....go get your codes scanned (Autozone does it for free).

I'm about 40 miles from one of the Fresno Autozone stores and taking the advice often given stopped there today for a code test. The ass't mgr. told me that Autozone no longer provides this service and hasn't done so for about 2 years. He said 'auto dealers' sued them for infringement on their business....And so I'll shop for a reset too. In my research I've found two 'important notices' about the OBD ll scanner.........the notice states that many brands will 'not' provide sufficient data for BMW cars. This seems to be the case for the brand Autel. Peak seems to be the correct scanner for BMW cars and the price level is fairly consistent @ about $140 (R5/FX3). I have replaced the my fuel with premium....drove about 100 miles today.......car is normal....just the Service engine soon light remains on. Jonzie

The fact that it came on after filling MIGHT indicate a loose gas cap, or defect seal on the gas cap. Make sure it's actually in tightly and that there aren't obvious flaws in the gasket. Then drive for a week and see if it goes off.