HEGO sensor circuit indicates system lean (right side) I did reset the computer before I changed the o2 sensors. I thought it might be a good thing to do because i'm approaching 300,000 km and i'm unsure if they have been done in the past, and the concensus on here is that it seems to reduce mileage and power and not throw a CEL, because the EEC-IV has too much tolerance in O2 sensor readings, or the sensors just get lazy. I left the battery unplugged the night before I changed them. All seems well and it drives well but it throws a Code 172 a few minutes after driving. CEL seems to come and go as you're driving at first, but after that first few minutes when it comes on, it seems to stay on now. No KOEO off codes. Do I have a dud o2 sensor? Or is it just detecting a lean condition on the passenger's side? It seems to drive really great, but I won't know if i'm saving gas until I fill up the tank.