Ford focus engine light!!!

I own a ford focus 1.6 ghia 2004. I have had constant problems with the engine light coming on over the last 2 years. The garage I took it too has had it on the computer each time it comes on, which apparently narrows the fault down too the lambda sensors and the Cat. Now all of these components have been changed, after 5 months the problem has re-oocured, to be honest it also has the guy at the garage flummoxed, as he cannot see any faults with the parts that have been changed.the Car is running fine, feels no different to before light coming on... any suggestions would be greatly appreciated.
Cheers
Colin

Curious as to any other drivablility concerns? A very common cause of o2 sensor (lamda) and catalytic converter curruption can be a rich running condition. This can be caused by things like faulty fuel injectors,etc. Having a shop perform an injector balance test, may be a good place to start. Ignition coils (especially Coil On Plug) style are known to fail causing a rich condition as well............just a couple of thoughts.

Hi, no there are no other issues, car seems to be running perfectly fine, however when or if the light comes back on, I will mention this to the mechanic. Many thanks for your reply