Hi, I own a 2016 Ford Focus 1.0 Ecoboost. It is well known that cats of these engines do not last long. Mine failed too. I have EML popping up constantly on a motorway. No problems with city driving though. Since the Ford OEM cats are quite expensive, is there any reliable aftermarket alternative you can recommend based on your experience? Thanks in advance ...

Well, I have the cat replaced yesterday at Ford dealer. Today I have a 100 miles trip and during the first few miles the check engine light came up again with the same code p0420. I cleared it and EML gone and did not return till the end of the trip but I noticed the there still exist a permanent  code p0420 in the ECU memory I guess. Do I have to make some longer driving cycle for the engine management to understand the new situation or I have to check something else?

So the new one is a ceramic catalyst?

If it turns on again better go to the dealer to check it.

I would suggest a 200 cpsi metallic euro 6 catalyst.

It is a Ford OEM catalyst so I guess it is metallic one. I give up on the idea of buying aftermarket catalyst since most are not reliable.

If it is Ford then most probably it is ceramic. I have 200 cpsi (sport) metallic one, no issues so far.

Do you know for sure it was the cat that needed replacement?

The code you mention could also appear for other reasons.

Well, it was the mechanic who diagnosed it. He said that with the faulty oxygen sensors there should be a different code. Also the code only popped up on the motorway driving at high speed and never within the city driving cycle.

Some news from me and my battle. As I said a few miles after cat being replaced I had check engine light on with the same code p0420. I cleared it and have passed 200 miles after with no other issues. Today when I came back home with NO engine warning light I decided to check if the p0420 permanent code still exist hoping that with some driving cycles the code is cleared and everything is fine now. When I connected my OBD scanner guess what I found - p0420 was absent instead there was p0036 with NO check engine light on. This is the first time I detect this code for almost two years since I have this problem. In all cases in which the check engine light was on there was p0420 with no other codes. Any advice?

I can only re-iterate what I previously suggested. Do you know if the heated oxygen sensor has ever been replaced?

Nb. Not the same indications as your car, but my vehicle had a new aftermarket cat and the upstream sensor replaced in July 2020 but still occasionally throws up the P0420 code. 

No, as far as I know it is the original one. If you have replaced the cat and upstream sensor how you can explain p0420 code in your case and how often it occurs? 

27 minutes ago, Tony Roman said:

No, as far as I know it is the original one. If you have replaced the cat and upstream sensor how you can explain p0420 code in your case and how often it occurs? 

At the moment I can't explain it except to say I haven't yet tested the sensor readings using Forscan.

It would seem that many people assume the cat or sensors are the problem but that's not always the case. A quick look online reveals that other problems can trigger the P0420 code.

In your case you have a new cat but neither the upstream or downstream sensors have been replaced or checked. If the codes bother you I would suggest you get that checked next before investigating less likely issues.

Good luck!

Thanks a lot for your help, Ray!