MaryK

I need some help, please, guys!

I've replaced the catalytic converter in my 2003 Accord LX twice in the past 5 yrs...both times at the dealer. I've also replaced the O2 sensor. Since then, the CEL is nearly always on, with a reading of P0420 (catalytic converter). 114k miles when I bought the car 5 yrs ago; 179k miles now on the car.

Today I took my car for its annual MA-required inspection, and failed because of the P0420 code readout. The state will not let me drive the car until this is fixed. Clearly the dealership has no clue what the cause is.

Any ideas out there?

Thank you!

poorman212

There are a few things that can and will cause "cats" to fail early.

What are the fuel trims reading?

Are there any exhaust leaks in the exhaust system

hondapro87

100% correct you need to find the cause that is causing the convertors to fail early

Accordian47

Usually they fail due to misfires or an improper air/fuel ratio allowing unburnt fuel to build up and burn in the cat. The code however can still be caused by other things like exhaust leaks, the ecu cross references the readings from the upstream o2 sensor (air fuel ratio sensor) and the downstream (post cat o2 sensor) to determine if the cat is effectively reducing emissions (post cat o2 should read differently from the upstream if the cat is working). Exhaust leaks allow exhaust gases to exit the exhaust stream and also allow atmospheric air in, changing the readings on your sensors.