O2 Sensors - 1999 Dodge Ram 1500 Van

All,

The "test engine" light on my wife's 1999 Dodge Ram 1500 van came on today. I put a OBDII tester on it and it showed a P0138 code meaning "O2 Sensor Circuit High Volts (Bank 1, Sensor 2). I crawled under the van and found two O2 sensors, one before and one after the catalytic converter.

Does anyone know which sensor is the one indicated (bank 1, sensor 2)?

Thanks!

Dave Young