I got a code of p420 that saying its an cat but my MIL goes off and than goes back on and than comes back on. I went to lincoln tech for automotive and one of my teachers worked for audi and it says that with the 2003 1.8t a4 when that code is present it is the maf sensor. I believe him an all because he wrote an article about the entire problem but is there any second options on this problem before I change the maf sensor ? Thanks

 

P420 isn't a code, all DTC codes are 5 digits which means your missing a number.


If it is P0420 - Catalyst System,Bank1 Efficiency Below Threshold

It could just mean your post cat 02 sensor might be going bad or your cat might need to be changed.

If it was a MAF sensor issue you would end up getting a MAF code.