Hi, I run a Citroen C4 1.6 hatchback auto 2005. I had an error message showing on my dash "anti-pollution failure". I had hoped it maybe a faulty sensor or a leaky joint but Yeomens Citroen diagnosed a failing catalytic converter and a failing coil pack (producing a slight misfire). I understand a misfire may not totally burn fuel which can in turn start to break down the catalytic converter. However, for the moment I cannot detect any obvious misfire or poor peformance. I am resigned to the fact that both the coil pack and converter will need exchanging. I am not prepared to go down the route of shelling out close to £900 (£200 for the coil pack and £700 for the cat) to Yeomens to exchange and fit these items. Instead I have sourced a coil pack for less than £40 (with 2 year warrenty) which I shall fit myself. The catalytic converter is not so straight forward. I have found a mechanic who would be happy to fit a cat that I can supply. Trouble is at this stage I am not sure which I can buy, so I am seeking members' advise. When I go to large discount retailers such as Eurocarparts, I input the vehicle reg which then leads to the "correct" cat for my vehicle. This has an SKU code: 724 731 310 and is in the region of £145. However, if I carry out a more general search for a cat to fit a C4 1.6 2005 numerous suppliers offer a cat with an SKU code: 724 730 300 in the region of £70. Both these cats appear to look identical and have the same spec. Naturally I would like to get away with spending as little as I can but do not want to buy a part that will either not fit, perform or create a fault code. Any thoughts?