I cleaned the MAF, ran a cycle of Cataclean through it, changed air filter, going to reset and take a pic of the codes if they show back up.

When’s The last time the rear O2 sensor was changed? That’s usually the one responsible for showing cat inefficiency codes. Look there 1st to make sure it’s operating correctly

Ryan, I havent ever changed it. The X5 is a 2010, and I have only had it for a year and a half, P0420 is the current code that comes up within 50 miles of resetting.

Thanks for the replys and suggestions.

Tom M

If you can do some monitoring of the sensors I would. Or hell, at that age and mileage, just replace both sensors. They are due