A warning light has appeared on my dashboard, which according to the manual means that the "engine's emissions control systems may have a problem". I will of course be taking it to be checked out, but before I do so I am curious to know any opinions of what is likely to be causing this. The car had a new exhaust & catalytic converter fitted only a few months ago.

The day before this light came on I had a new battery fitted, and I am wondering if this could somehow be causing the problem - dodgy connection?