Hi Bill. Check for dirty and or corroded connections at the O2 sensors and any connections in between all the way to the PCM. Also check the wireing for damage, especially near areas of heat. You may have to remove the corrugated covering on the wires in areas of high heat. I've seen some instances on other cars that the corrugated tubing had a higher temp rating than the insulation of the wires. The corrugated tubing looked fine but the insulation on the wires inside looked melted. All it takes is a little melting and a little water inside the cover to mess things up.
As an example. A while back Ford found that the wireing to the rear ABS sensors was too close to the exhaust on some cars. The wireing inside the corrugated tubing was melted but the corrugated tubing itself looked fine. These cars were throwing ABS codes And the techs couldn't figure out why, until someone disected the harness to the sensors.
This example happend at New England Dragway. The owner of the car never drove it in the rain. He spins his tires in the waterbox and his ABS light started flashing.
I hope this helps. Good luck, George.