So for a 2002 it sucks, but I got a check engine light, Scanned it, and it turns out to be p0031 - wich is apparently an o2 heater circuit. The problem is there is 2 o2 sensor.. So which one needs to be replaced?? or how can I check?The dealer wants $70 to scan it.. and tell me which one to replace - not really in my budget. HELP!

you may not need an O2 but rather an ECM. if you have a volt meter you would need to check the heater circuit on the O2 at idle the ecm side of the heater should read 0 to 1.0volts. if it reads battery voltage on both sides then your ECM is not grounding the circuit. This is not all that uncommon. I cant give you the wire colors for that code at the moment as I dont have a service manual handy here at home. but I think that is the HO2S2B1 [Heated Oxygen Sensor 2 Bank 1] This would be one of the 2 lower sensors I believe the one toward the belts.