The check engine light came on in my 1987 Eldorado. This has not happened in many years. The reading I got on the display said ARE which didn't mean anything to me so I took it to a shop that specializes in older GM cars and who has repaired this car for years . His diagnosis was a problem with the O2 sensor and the engine ECU. Since the check engine light came on the engine has actually been running smoother than ever before. The light comes on and goes off intermittently but the engine function seems to be fine. Is there anyone who repairs the engine ECU? Should I replace the oxygen sensor? I just spent $1000 on a new headliner and taking some scratches out of the paint so the car looks as if it just came out of the showroom inside and outso I hate to give up on it especially when it is also running really quietly and smoothly. What to do?