Code P0016 is usually assciated with worn camshaft drive (stretched chain is a bit of a misnomer). It can, in some cases, also be caused by a faulty variator, or a faulty variator solenoid. Depending on what was changed when the chain was las replaced, it may be worth trying a new solenoid; they're relatively inexpensive and an easy DIY change.
These solenoids seem to be an Alfa-only part (as are the variators), but the good news is that the chains and associated parts are the same as the Vauxhall Z22SE engine, meaning that they can be sourced far cheaper than buying from Alfa.
I see quite a few of these, and most of the problem is, in my opinion, caused by overly-long service intervals. I strongly recommend that anyone with a 2.2jts or 3.2jts (yes, they suffer too) changes their oil every 12k or every year, using a quality full-synthetic oil.
I recently changed both my chain and my exhaust solenoid because of P0013 and P0014 error codes. I only needed to have changed the solenoid in the end. See the thread on it here
. From my reading up on the subject, P0016 is strongly associated with a stretched chain.
However, the best advise I could give you is to get it to a garage for a proper diagnostic: the fault codes only scratch the surface compared to the diagnostics an Alfa specialist would have. You don't want to spend a lot of money on a fix that won't fix it!
If it is the chain, the replacement kit usually comes with the chain, new tensioners and some of the cogs the chain wraps around, though not all of them. To change the remaining cogs is expensive, another ~£300 on top of the £550 the new chain kit will cost you. If the chain has worn through 3 times, odds are those other cogs will need replacing too. As others have said, regular annual or 10-12k oil changes will stop it from re-occurring. It happens because the pipe leading to the separate "chain section" is very narrow, so as crap in the oil builds up in the pipe over time and mileage, it blocks the pipe and the chain continues to rotate with poor lubrication leading to excessive wear.
And sorry for the lack of proper technical lingo, I'm no mechanic! Just passing on what I was told by one.