My bil has a 2005 Durango 5.7 hemi with about 95,000 miles on the odometer. The last year or so the check engine light has gone on and off several times-but usually stayed off for the most part. I scanned it at least twice in this period and never found a fault. Recently it has gone on and stayed on. The truck has no apparent symptoms. I, yesterday, scanned for codes with 2 different scanners and both report "no codes" despite the fact that the check engine light is on. Any ideas?

What scan tool are you using? If the check engine light came on but is off now there will be codes stored with environmental data. Get it to the dealer and get it checked and there is a good possibility that it needs a flash update.