Hi! 2010 Outlander V6. 210,000 Km on the odometer. Getting this code (P0421)for an engine light that’s been going on and off (couple weeks at a time) for the last few months. This Site says cat is the #1 cause for this code. I’ve got no cat failure symptoms (reduced power/acceleration, no black smoke, idle is smooth, vehicle starts up fine, etc). I’m planning to swap out the downstream o2 sensor this weekend to see if that’s the issue. Anything else I should be looking for/doing?

 

Had a similar issue but it was due to low quality fuel. Try running higher octane fuel to see if it clears it up.

 

Will do! Thanks for that. Also had a thought that it might be just that the sensors are picking up the beginnings of a problem, so ran some catalytic converter cleaner in the fuel, and that’s turned the light off for now. Still going to do the sensor as well to see if the light stays off.