A common emissions code seen in the field, a P0420 trouble code indicates that the catalytic converter isn't functioning efficiently

Ok so this is the fault I'm getting from my fiesta but before buying a new cat I want to try this below liquimoly catalytic system cleaner. 

Has anyone used this before successfully?

Also it says it needs sprayed in to the intake while the engine is running but all the examples I've seen on YouTube don't have the intake in the same spot as mine. Would anyone know the best place to spray this in to, a picture or diagram would be a great help if possible! Below is a pic for reference (not my car)

 

 

 

Half of your engine seems to be missing in that picture.

Easiest way to access the intake is to remove the pipe clamp on the left hand side of the turbo (not visible in pic) and then spray directly into the turbo intake.

I have no experience with this specific product so can't advise on that.

Comes out well in this (US) review:

https://www.autoguide.com/best-catalytic-converter-cleaners

It's just as likely that the sensor, or wiring, is throwing the p420, rather than there being anything wrong with the cat.  You should find out what the problem is before buying the most expensive link in the chain.

I have a better pic below if anyone can direct me to where this solution should be poured:

9 hours ago, Leezer said:

I have a better pic below if anyone can direct me to where this solution should be poured:

Poured?  If it's a liquid don't pour that into the intake!!   If it's a fine mist spray you can spray that into the turbo inlet.

Debatable whether that's a better picture of the engine bay.   I'll try to mark up one on my phone later, easier than doing it on the laptop where I am now.

Green arrow shows direction of spray into turbo intake.  You will need to loosen the jubilee clamp and remove the rubber joining hose there for access to the intake.

Absolutely do not pour any liquid in there.  The engine will suffer catastrophic failure if you do.

I wouldn't be spraying anything in just yet, in fact I wouldn't ever be spraying anything ever! 

Get your emissions tested at a garage. The figures will tell you a lot about the condition of the cat and help pinpoint what the issue might be.