Why has my son's Ford Focus showed erroneous fault codes when diagnostically checked?

The engine warning light on my sons' 2002 Ford Focus 1.6 LX Estate illuminated about four months ago. He had it checked by a main dealer and was told the code indicated the Catalytic Convertor was defective. The engine warning light recently illuminated again and he had it checked at a local garage. This time, seven codes were reported including the Catalytic Convertor and the ABS. The only problem is, this model doesn't have ABS, so I'm starting to smell a rat! The car continues to run perfectly in all other respects. Both times the warning light has illuminated after a long run, and there have been no long runs in the intervening period. Has anybody any idea what's going on?

Asked on 1 September 2010 by Jeffers

Answered by Honest John
Might be the exhaust manifold lambda sensor. The multiple fault codes were obviously in error.
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