2011 Amarok dpf light on then flashing glow plugs

[Wiganer06]

After a routine 12month service and a new starter motor fitted, my car has thrown a dpf warning light followed by a flashing glow plug and car going into limp mode. I took the car back to the garage and he checked it over and said the dpf isn't blocked but it's thrown a temp sensor warning code from the inlet on the dpf??? I'm a car painter by trade and not too clued up on engines etc, is this a common fault or could there be something more sinister? He cleared the codes and after a few days driving same problem. It's booked in at the main dealer for a diagnostic check to make sure its the sensor any info would be greatly appreciated thanks people