Hi Everyone,
I have the P0420 code which states "Catalyst System Efficiency Below Threshold(Bank 1). Also have yellow engine light. Bought the car new in 2008 and now has 158k miles on it.

Runs great but uses oil about 1 qt. per thousand miles. Probably need to replace valve seals but not anxious to spend the dollars. I'm guessing the cat is shot, but how can I be sure without spending $900 on a new cat? How can I test the sensors to rule them out?

Using the Torque app on an old Samsung Galaxy 3, to read codes.


Thanks in advance for your help!

 

I thought more about the situation and bought both oxygen sensors for about $220 online. I replaced the sensors yesterday and ran some errands and short trips after I was finished. The check engine light went out after restarting the Mini about four times. If the check engine light comes back on I'll update the thread but it seems that one of the sensors was bad. Both sensors were original, so I can't complain since they have 159K miles on them.