temp sensors and immobiliser

[nat hart28]

hi does any one know how to reset the ecu after I have changed the temp sensor, put the car on diagnostics and it said that the coolant temp was -39 I have since replaced the sensors and the readings are still -39 and could this reading stop the car starting, also on diagnostics i have noticed that the immobiliser stays active even tho the signal is received can any one help, please could some body also please send me a diagram of the position of all the sensors and anything else that might help get my car running thanks nat