key problem

Ok, so I admit I was an eejit, when I believed the previous owner when he handed me 2 keys and said "oh the spare key needs a new battery".

Can't complain I guess, because I got the car for a good price.

I have 2 x 2-button "long" flip-out keys.

One works, one doesn't.

Having swapped the batteries from one to the other, and interchanged both halves of both keys with one another, I have established that it is the "electronic" half of one of the keys that doesn't work (starts engine though).

So, my question is, what is my cheapest option to either get this fixed, or, source a replacement.

Hello again (again)

The way you're going with your new purchase I would suggest you invest in a Lexia tool (or clone), available from popular auction websites

Lexia will make solving problems like this a while lot easier and gives you the same diagnostic capability as a Citroen dealer.

Before you start on this problem I would suggest you get a couple of brand new, fresh batteries. A least then you know that your power sources are good and it removes the danger of getting flat and good batteries mixed up while trying different things.

There are a few possibilities with your keyfob, firstly, the key may just need re-syncing to the car. If a key isn't used for some time the car looses track of it's rolling code, hence the re-sync.

This goes something like, start the car with the key attached to the fob and then press one of the buttons. I may not be 100% with this, no doubt someone else will jump in to help.

The second possibility is that the fob has never been programmed to the car. As it's attached to a working key this is unlikely, however this is where Lexia is useful, you can look to see how many keys/fobs are programmed to the car.

Another option is that the fob is broken. You can test basic function with a key fob tester. These give a go no-go indication if the fob is sending a signal, but not that the signal is correct for the car. And again, Lexia can help further by allowing you to look within the car's signalling to see if it's receiving anything when the fob is operated.