Are they interchangeable upstream to downstream or vise-versa? When I went to LT's I only used two of the four(the upsteam ones) and still have the 2 after the cat sensors in my garage. I will find out first but I think I might have burned one out...
Matt

 

the connectors are different, they are side to side, but not front to back

 

I used a scanner at the local auto parts store and got P0155- Heated Oxygen Sensor (HO2S) Heater Circuit Bank 2 Sensor 1.

 

That's the primary O2 sensor on the passenger side. A new one is ~$30

Make sure there isn't a problem such as wires burnt by your headers

 

Thanks!
Matt