Hey Guys,

Had the check engine light in the 2005 F150 (90,000 miles) come on. Got the code checked and its P0420. I know that has to do with the cat threshold levels etc. so i believe im looking to replace the o2 sensor, if im not mistaken.

How hard of a job is this? Ive done a decent amount of engine work and worked in a shop in high school. Just looking to see if that is the right thing to try first, replacing the sensor, before replacing the cat.

Also I know its the right bank, but if im not mistaken there is a before and after the cat o2 sensor, which do i replace? Both?

Brian