I just had a wider diameter B-pipe installed on my GSR. I had to match 2 pieces from 2 exhausts that I picked up here and there, so I had them weld extensions. It's now 60mm. Before that I had a DC header, and an ITR muffler and had no problems, except that I could hear the bottlenecked air. Right after I left the shop I got the CEL.

Will resetting the ECU do the trick? TIA for any suggestions.

 

Actually before resting the ecu try to get the code out... (look for the service connector and jump it, the cel will start blinking and the amount of times it blinks, that is your code) Then you can find out what is wrong...After that reset the ecu.

 

Thanks, I'll try that tomorrow. I suspect it could be just an old failing O2 sensor, since the car now has over 100K? The shop denied having touched the cat and the O2 sensor, and they had no reason to unless they made a mistake.