hey guys I've an 2003 A4 1.8t my check engine light comes on and I got it scanned and the code erros is p0420 and says catalytic converter below efficency when I got the light reset I drove it 700 km and light came back on gave the exact same error and I haven't driven it much since and I started my car after 4days and the light was gone does anyone knows how to fix this problem it's a on going thing check engine light comes on goes off.. I wud highly appreciate if someone wud be able to help me out.

 

coilpacks or plugs would be ur first option. also check ur vaccume lines. make sure there is no leaks.

 

The code has to do with ECU not seeing what it expects from the O2 sensor reading the catalytic converter. It could be either one of them dying.

Google "p0420 A4".