Over the past couple of months I have had the engine systems fault warning light coming on intermittently on my 1.6 56 tdci focus.

Its getting more frequent but my car is driving perfectly fine even when the light is on. It comes on for a few miles and then goes away the soon after.

I hope it is something as minor as a faulty sensor rather than something more expensive.

I have just put a new battery, alternator and timing belt in and I also have had my DPF removed - so it shouldn't be those that's faulty.

Have you guys any advice on what could solve the problem? Like I said - the car is driving great apart from that annoying light!