I realise this is quite an old thread but this video explains which sensor it is and how to change it. Basically it's just a temperature sensor for the dpf. There are 3 so if one is registering a different temperature compared to the others it flags up this fault code. P242A Fault - Exhaust Gas Temperature Sensor (EGTS) B1 S3 Fix VW Golf VI MK6 1.6 TDI - YouTube