Engine in I assume limp mode sent it to garage to have rear coolant pipe replaced ie egr valve to thermostadt housing they returned the car in limp mode and wouldn't take responsibility have cleared dlls but after startup returns with service engine .have changed sensor in airbox also boost pressure sensor under turbo and again put new map sensor in on intercooler pipe to egr valve .just after startup still returns po298 and puts engine in limp mode have also pushed actuator rod to see if it had seized moved freely  anyone shed any light on it please 

P0298 means it has overheated at some point possibly before the coolant pipe was replaced. I would get it diagnosed before the worst happens.

Possible causes for this P0298 code may include:

An engine cooling system condition that has resulted in engine overheating

Defective engine oil temperature sensor

Open or shorted circuit

Corroded wiring and/or connectors

Low oil level.

The car prior to going to the garage to have hose changed drove perfectly was aware of leaking pipe and kept on top of it once I had replacement took it to garage to be replaced garage returned car in limp mode and disclaimed it left me with it it run perfectly prior to garage