Ive recently had the P420 error on my Focus MK3. Initally just cleared with a cheapy Streetwise reader. Passed its MOT but they did say it was close on emissions.

Code has come back so ran some catclean through the engine. Seemed to work, but its come back, again.

Got an Vlinker FD+ and ran some cat tests which come back indicative of a failed cat - sensors working well, but o2S12V is swinging from 0.03v to 0.83v.

Whilst I may have to accept my fate on this, but if worst comes to the worst, I'd be looking to do the job myself but I cant seem to find any real guidance or videos on it.

I dont have th Haynes manual for this car, I'd be inclined to buy it if it did cover cat replacement?

Alternatively, is there anything else I might be able to try instead of replacing the cat?

Haynes does cover removal and refitting but the description is very brief - 4 paragraphs for removal and 2 for refitting - plus a few photographs.

This is such an easy job I'm not surprised there are no videos.

It's the same shape and location as the DPF on 1.6 TDCI so you might be able to find videos on that for a rough idea. It's literally just heatshield off, V-Band clamp off, rear pipe bolts off, then mounting bolts.

I strongly suggest installing an original catalytic converter unless you are planning to sell the car within the next Year.

Aftermarket catalytic converters contain a lot less precious metals (this explains the significant price difference) and have a much shorter life expectancy. On a 1.0 EcoBoost it is quite common for an aftermarket catalytic converter to show the exact same symptoms due to decreased efficiency within a year or two.