oxygen sensor heater circuit

on my 1999 ck1500 that matches the 1998 wiring diagrams, I am getting codes p0141 and po161
which is bank 1 sensor 2 heater circuit and bank 2 sensor 2 heater circuit failure. both sensors measure about 4 ohms at the sensor and according to the diagram are directly fused by the eng-1 fuse. how can the obdii report heater failure when the heaters are not sensed by the system.

If you are getting a heater code for both rear o2 sensors, most likely it is not the 02 sensors thesmselves. i would check to make sure they are getting power and make sure the fuse for that circuit is ok.