Hi my husbands legacy has a intermittent engine management light on and is showing a p0420 fault code !! Local dealer said it was a AS sensor that needed cleaning , and did so at a cost of over £400 , we were told the sensor may need replacement , and if engine management light came back on to return the car for replacement.
On trying to book the car in for the sensor replacement I was told this May not be the fault and it could be any reason why the engine management light has re occurred .
I took the car yesterday to a local garage for a diagnostic check and the p0420 fault came up , there answer was to replace the cat ????
Where can I take the car to get the fault diagnosed correctly a new cat seems a little ott and why didn't the main dealership replace this sensor at the time , cleaning it seems stupidity .We live in North Yorkshire