I just replaced the main engine wire harness on my '95 C280. After 8 miles, my check engine light came on. I don't have a scanner and I doubt anything is wrong. Should I take it to a shop to have the code read and reset, or should I just disconnect the battery and hopefully the check engine light will go off? I have read about the ECU retraining after the battery was disconnected. Is there anything to this? Any specific procedure? Do I just drive the car and wait for the light to go off? Please advise on how to proceed. Thanks.

 

What I do in this situation is disconnect the battery, reconnect, and hope for the best. Not very elegant, but 95% of the time the CEL won't set again. I do this first mostly for the fact that it's totally free. If the problem is no longer present, you can just wait for the light to go out. It takes a few keystarts. How many depends on what the problem was.

"ECU retraining" comes naturally through driving the car. You can speed the process, but you won't get any advantage from doing so, except to pass an OBDII emissions test in some states. They can tell if you've just reset the ECU.

It takes some idling, some stop and go, some highway driving and a few other things to "retrain" everything. You can do it in less than 20 miles if you track all the parameters on a scan tool. But, like I said, why bother?