My 2010 Oddy Touring set a P0420 today just after I had a tire pressure sensor replaced, and I can not turn off the Check Engine light or erase the code with my Ultragauge. Both bank 1 and bank 2 downstream O2 sensors seem to be running about a half volt as they should, but the P0420 will not go away. A friend who adjudicates claims for insurance companies and has experience with many vehicles said some manufacturers require that some codes can only be reset by a dealer. Might this P0420 be one of those? Anyone know? I've never had the Ultragauge fail to reset a CEL on any vehicle before, but I've not had a CEL on the Odyssey before this.