Hi guys,

Recently a Punto Mk2b owner and having the EOBD light coming on.
Bought the car at 75,000 miles and it first lit after approx. 1000 miles. Took it to a friend with an OBD2 scanner and got a P0420 error code; unfortunately, not the most specific of codes to know exactly where the fault lies.
Decided to clear and drove again around 1000 miles before it lit a second time; however, when I went to use it the next day the light had gone. Assumed (poorly) nothing was too serious and went about my day as usual.
It's now lit again around 500 more miles down the road and, with it's MOT coming up next month, it's something I need to get on top off. Would anybody know more specifically what may be the cause? Looking into getting my own OBD scanner this week but, for the moment, I'm assuming it's probably the same fault code.

Also, a little confused with what to buy OBD related. Will any generic scanner work? I've seen mentioning of different things such as ELM327 which makes it a bit confusing. Is anybody able to link an OBD diagnostic tool they've found useful?

I have a VAG cable on order as I've also got the common airbag lights showing up but I'm assuming this probably won't work when it comes for searching for engine codes?

ELM327 ia a USB lead to connect the port on the car to a USB port on a Laptop to use Fiat Multiecuscan. EBAY is usually a good place to look for these sort of leads.
MES can be downloaded and used for free from http://www.multiecuscan.net/ although the registered version (50 Euros) allows you to do more.
Generally that is considered the better option than a generic OBD

P0420 looking it up suggests it’s an exhaust gas problem so it’s fairly telling what’s going on.

Either you need a new 02 sensor in the exhaust or you need a new catalytic convertor. It’s probably hovering around the threshold which is why it’s intermittent as you describe.

You could always try an “Italian tune up” which essentially involves driving it hard and getting the engine nice and warmed up to blow out and burn off any crud that has built up in the engine

I'd heard of the Italian method before; I did it across a 20 mile trip along the M3 and it did seem to get me a few hundred miles further before the light lit again but it doesn't seem to have fixed the issue.

When you say "02" I'm assuming you mean O2 for oxygen (looks a bit weird when you use a zero instead of the letter). I'm also gonna make a fairly obvious assumption an oxygen sensor is much cheaper than a ful cat replacement so is it worth making that replacement first and then waiting to see if the error comes back?

It's a difficult one to fully diagnose without getting the emissions measured by a professional as there is quite a large gap between each time it trips the error so I'll never really know it's definitely worked until I put a lot more distance into the car.

usually means the cat is at the end of its life and needs replacement
choose wisely as theres 2 different types on mk2 punto depending on engine but not a lot of people realise this
new cheap copies often fail at the next test as they are built to a price

I had this same code on my 2005 1.2 8 V last year. The car had around 210.000 km on the clock (so approx double of what your car have).
Replaced the O2 sensor after the CAT and cleared the code. It has not come back since.