a4 2001 engine management light on ,fault code says temp gauge not working

[fdt140876]

this is driving me mad.sometimes the gauge works but more often than none its not. the engine management light is on all the time. the heaters also only seem to get luke warm.have changed the coolant temp sensor still no change .

 

[murran]

what exactly is the fault code?
if its just a vague "fault in cooling system" code, its most likely picking up the thermostat being faulty thru the coolant temp sensor.

 

[fdt140876]

dont have a note of it at the moment.did a full dial sweep and gauge only flickered ?