Oxygen sensors no reading

I've been getting a P0420 code lately. When I check the Oxygen sensors
I get no data. I'm using the Auto Enginuity scan tool on a 98 XLT
(100,000km).

I was looking at the wiring diagrams last night and it looks like the
O2 sensors connect directly to the PCM. So, I'm wondering if there is a
possibility of a problem with the PCM? I have yet to crawl under and
backprobe the actual sensors. Just looking for some possibilities in
advance. I can't see all four sensor going kaput at the same time.

I've tried the scan tool on a couple of other cars and I was able to
see the sensors behaving properly.