So I'm new hear on this forum and I just bought an Audi a6 2002 I have had it for about a month and first the brakes go front and rear with rotors and now the check engine light! The obd code was p0431. Warm up catalyst efficiency Below threshold bank 2. Explanation: Air leak before catalytic converter. Cause: rich air fuel ratio or catalytic converter! Any body have this problem? What is a proven fix? I also recently reset the code, to see if it comes up again. Any suggestion?