View Full Version : Trouble Code P0420

11-14-2011, 07:13 PM
Hi Subaru Community,

Trouble Code P0420, Catalyst System Efficiency Below Threshold, on a 2002 Impreza, 2.5TS.

Replaced both oxygen sensors up and downstream, have heard a rumour it could be the catalytic converter. Can anyone confirm or deny, or personal experience?

Any advice would be appreciated, thanks in advance

11-15-2011, 12:01 AM
the p0420 is an ongoing problem, go to the dealership and see if you are covered for warranty replacement...the cat IS the problem.

11-15-2011, 05:46 PM
had the same problem on my first 2002 wrx. ended up being the catalytic converter.