Hi, there I am new to this group I have a focus 13 plate have fault code P0420 anyone experienced this code, what was the fault and cost to repair have looked up on Google and it mentions catalytic converter any help would be appreciated 

Welcome!
This says (as with all fault codes) that there may be multiple causes that need checking before simply replacing components (especially expensive ones):
https://www.engine-codes.com/p0420_ford.html

"We" also recommend Forscan and correct lead to ensure all Ford specific fault codes (rather than just standard OBD) are available.
Need to follow through on these checks and come back?

I haven't heard any bad reports about:
https://bmcats.com/
(If that is necessary BUT I'm sure someone will come back if they have 😉!

It usually is the cat on 1.0 EcoBoost with no noticeable symptoms.  We see a flood of P0420's every year as the weather gets colder.  The cat just can't maintain enough heat while cruising so it's efficiency drops below the ECU's predetermined threshold.  If the cat is getting weak, this is the time when it's going to show up.

 

If it's any other engine, then I would recommend further testing.

I have this problem on my sons car. So far been told its oxy sensors bank 1, catalytic converter or thermostat housing. Taking to another garage for a second opinion 

10 hours ago, Sam_76 said:

So far been told its oxy sensors bank 1, catalytic converter or thermostat housing.

It'll be the catalytic converter 🙁

11 hours ago, unofix said:

It'll be the catalytic converter 🙁

Not necessarily.  The other thread from that poster suggests there are multiple noticeable symptoms with their car.  Not the same as the majority of P0420 that we see.

On 11/26/2025 at 11:29 AM, Sam_76 said:

I have this problem on my sons car. So far been told its oxy sensors bank 1, catalytic converter or thermostat housing. Taking to another garage for a second opinion 

Thanks for the help yet to determine what the fault is hoping its the least expensive that for the help much appreciated 

On 11/26/2025 at 9:56 AM, TomsFocus said:

It usually is the cat on 1.0 EcoBoost with no noticeable symptoms.  We see a flood of P0420's every year as the weather gets colder.  The cat just can't maintain enough heat while cruising so it's efficiency drops below the ECU's predetermined threshold.  If the cat is getting weak, this is the time when it's going to show up.

 

If it's any other engine, then I would recommend further testing.

Yes mine is 1.0lt ecoboost do you know the cost of getting the cat replaced if that is the issue thanks for imformation 

On 11/26/2025 at 9:46 AM, Shearers said:

Welcome!
This says (as with all fault codes) that there may be multiple causes that need checking before simply replacing components (especially expensive ones):
https://www.engine-codes.com/p0420_ford.html

"We" also recommend Forscan and correct lead to ensure all Ford specific fault codes (rather than just standard OBD) are available.
Need to follow through on these checks and come back?

I haven't heard any bad reports about:
https://bmcats.com/
(If that is necessary BUT I'm sure someone will come back if they have 😉!

Thanks for help 

12 hours ago, Duncan Ferrier said:

Yes mine is 1.0lt ecoboost do you know the cost of getting the cat replaced if that is the issue thanks for imformation 

There are multiple options.

Around £300 for a cheap aftermarket cat.

Around £1500 genuine Ford.

Or have an exhaust shop fit a Sports Cat for somewhere in between.

May also have to pay additional costs for the lambda sensors if they are rusted in and cannot be removed without damage.