Hi, My Mini gave off a P0303 code over a week ago. I pulled the plugs and after almost 12,000 miles they were worn down quite far. I installed a new set of plugs, cleared the OBD error and drove the car but the error came right back after a short distance. Pulled the plugs back out the No 3 plug was clean. I plugged the coil and plug from cylinder #3 into the #1, 2 & 4 connectors and got spark on those but not No 3. Is there any chance the severely worn plug could have damaged the ECU? I unplugged the battery for a couple of hours too just in case I might clear something else...

Thanks