Your precats are probably nearing the end of their life. They're warranted for 8 years/80,000 miles. When mine started failing, the CEL would come on for a couple of days, then go off for a couple of weeks. Eventually, it stayed on full time. Since I had 100,000 miles at that time, the warranty wouldn't cover replacement of the precats, and the dealer recommended just leaving them alone if the car still ran OK. So my CEL has been on for the last 65,000 miles, and will probably stay on until the car hits the junkyard.
