When my V6 car is running, O2 sensor voltages on Measuring block 33 on both banks move vary sharply. O2 sensor resistance in Group 40, however, is much more stable. The Bentley spec. says the voltage should always be >.3 volts at 30Hz.

I'm not sure what 30Hz means, but I do know at times my voltages do go below .3 volts. In fact, in a logged drive, there were two instances where the voltage fell to as low as .02 volts and the O2 readings in the group also went to 0. O2 sensors on both banks were affected at the same time. No fault codes were thrown. Car does have a tendency to run rich, the primary issue I'm still trying to troubleshoot, maybe I found the problem?

Bentley manual says I may have a short to ground. Or, did the O2 sensors just decide to shutdown for some reason?

Based on this evidence should I start doing voltage/resistance tests on the O2 sensors and wiring?