Hi, Only joined the site today but I'm hoping you can offer me some much needed guidance here.
I bought my focus in March (2012), and after a couple of weeks suffered the annoying problem of the speed sensor failure, so the garage I bought it from kindly replaced the cluster and the speed sensor too. After a few more weeks the engine management light popped on, so took it to a couple of garages who tested it on a diagnostic machine showing the code 'Catalyst Efficiency Below Threshold', one garage immediately said they needed to change the CAT, but the second garage thought it only 'might possibly' be the CAT and so ran an emissions test on it. The car flew through the emissions test, and was told to run some Redex through it and get it serviced. The Engine Management light it still on and showing no signs of moving. The car runs totally fine, and every mechanic I take it to, hasn't the foggiest what it could be.

Ive read on another site that it could be a dodgy sensor??

Has anyone else come across anything like this or know what could be the solution for me please?

To make matters more confusing I tried the self DTC test on the dashboard and its showing that theres no fault codes :S

Try disconnecting the battery to reset the computer to see if it comes back again

Same thing came up on my wifes car yesterday. I put my code reader on it and erased the code. Took the car for a blast and its not come back on.

Its probably worth buying a code reader as they are only £20 on eBay and you can clear the codes yourself. Some redex may well do the trick. I have found that Cataclean works well also although I doubt it cleans the cat. It probably cleans the sensors and injectors.