2004 Rodeo O2 sensor heater circuit

[Rmasters3]

2004 Rodeo with the Direct Injection, 3.5L. Code scan says drivers side, downstream O2 sensor heater circuit is the reason for my CEL. O2 sensors (all 4) have been replaced. Heater circuit fuse checks good.

So where do I go from here? Not sure what's typically problematic in a heater circuit or how to check it.

Thanks