Take a look for codes. I realize the light isn't on..but have it checked. Clear them if possible and check again a day or two later. Hopefully it'll show up and give you soemthing to go on.
Otherwise..it's possible the sensor/bad wiring can give you false readings. Scottydoggs is the spokesperson here about how wiring gets crumbly and bad when it lives over exhaust for most of it's life... He'll likely pop in since I mentioned his name and give you the in's and out's of the potential wiring issue.
