J30 O2 Sensors

[scdanny]

I plan to address the o2 sensors soon since I have 104,000 Mi. on my car. Question; Should I change all 4 or only the rear sensors first(the forward sensors look to be a pain to get to). Do I have to reset anything or disconnect the battery for a period of time? Thanks, Danny

[Q451990]

I assume you have a 96 or 97 (OBDII)? I'd replace the fronts only... on most OBDII the rear sensors are a check for the fronts, and don't really control the mixture. The fronts are actually the ones that get sluggish and cause extra fuel consumption, etc. A bad rear sensor will trip the "Check Engine" light, but otherwise should be fine.

At least this is my understanding... I replaced just the front sensor on my 97 truck with 105K and noticed a substantial increase in gas mileage and lean/rich cycle with the ECU test mode monitor.

Heath