Hello all, this is my 1st post on here it's not a good one. i will start from the begining. I have a ford fiesta zetec-s (MK5) I have a miltek full system exhaust which was fitted in april 2005, just after an MOT. Shortly after i had it fitted the 'engine warning light' came on so i phoned the company who fitted the exhaust and they told me it was becasue of the 2nd lambda sensor (the one after the cat) was not connected to the exhaust and i was just to hang it below the car in fresh air, which i did. And also to pull some fuses and replace them again to get rid of the light. The MOT of 2006 passed no problems. Shortly after the 'engine warning light' came back on. I bought and installed a 'bluefin' from superchips at this time, the 'engine warning light' went out when i did this but later came back on. i always get rid of the 'engine warning light' before an MOT and the MOT of 2007 just passed on the emissions! now i cant remember if the bluefin was installed or not while under the MOT. just before the mot of 2008 i had the 2nd lambda sensor reattached and reset the fault codes. now the problem........MOT of 2008 Failed! high hydrocarbons! the 'engine warning light' is on and giving a DTC P0420 Catalyst system below threshold (bank 1). What does this mean? is my cat done for or do you think it could be a sensor problem as it was hanging under the car for ages?