Hi new member.

Strange things happening on my wife's Focus 1.8 petrol 2009 the engine light comes on and the codes 420 so I know what that is but if she drives it back and forward to work which is a 30 mile round trip on back roads the code will come on after a couple of days. I cleared it this morning before leaving on a trip to the inlaws in Hertfordshire which is about the 200 mile round trip and the light stayed off until we got back into Leicester and driving slowly in the traffic and then it comes back up so I'm wondering whether it is still the cats or sensor or something else I wonder if anybody else has had this problem.

 It had a service two months ago but the plugs were not changed as they are not due till next year because it's to yearly on the 1.8 Focus. Car runs absolutely fine no smoke fuel consumption still pretty good around 50 miles per gallon on a long trip so I don't really want to take it to the garage and fork out on a cat when I don't think it needs it because its very strange.

 

Thanks in advance Martin

hi, you need to get the hego sensor wave forms checked so you can determine whether cat or sensors need replacing. not difficult if you have appropriate equipment.