I have a 2000 legacy wagon, the CEL light has come on 2x and each time they dealer replaced the O2 sensor and the light went out. It recently came on again, I took it back to the dealer and the computer showed a code P0420. They said the catalytic converter was ruined and for $1017 they could replace it for me. I declined the service and as I was leaving the tech told me I probably made the right decision. He reset the light and he said unless it comes back on, I’m ok. Why they didn’t tell me that before they recommended the $1000 repair I can’t understand – beware out there

 

-cbrown

P0420 is «catalyst system efficiency below threshold».

The FSM indicates that this code could also be triggered by a fault with either O2 sensors circuit (upstream and downstream). If so, there should also have been another code indicating that. But maybe it would not have been in the dealer's interest to let you know that...

Moreover, even with no O2 sensors at fault, the P0420 code could be triggered by a leak in the exhaust system (air entering the exhaust system).

Finaly the FSM states that you have to inspect the inside of the cat converter before deciding it's bad. You dont say they did that.

I also think you were right in at least posponing that costly replacement.

Hope that helps.

SOA REALLY needs to do something about dealer ethics.

 

We've had the 02 sensor replaced twice (both on warranty) on our '00 Legfacy wagon and we still get intermittant bogus CELs. After 46,000 trouble free miles we have learned to ignore it.

 

If you are in an emissions check state you can:

 

1. Do the battery dance just around the corner from the inspection station so the codes have cleared and the light is off for your check.

 

2. Move to Montana ;-)