I have two trouble codes causing the Check Engine light to be on; P0155- Heated Oxygen Sensor Heater Circuit 2 S1 P0161- Heated Oxygen Sensor Heater Circuit 2 S2 The car is a 1997 Thunderbird with a 4.6 It has an after market exhaust system with cats. It's an electrical problem but I have no idea where to begin in trying to find it. Has anyone dealt with this or a similar problem before? Any pointers would be appreciated. Also, Could anyone tell me what bank (drivers side or passengers side) those codes are coming from? Thanks.