This is my first post so hope I am in the right place for this query!

I have a MY04 9-5 Aero in Sydney, Australia. Have a long term ongoing issue with engine temperature guage "tripping" ie falling to off position at any time from moments after starting engine to hours into a long trip. If the aircon is on it will trip the compressor out. Usually, switching engine off and restarting will immediately fix the problem for minutes, days or weeks if I am lucky. Fault code reads "P0118 ENGINE COOLANT TEMP.SNSR CIRCUIT SHORT TO B+ / OPEN CIRCUIT.

Fitted new engine coolant temp sensor, no difference. Auto electrician traced problem to EMH engine management harness bad connection. The wire running to the sensor had a loose connection which was rectified. An extra earth was added to the harness prior to reinstallation prevent problem from recurring. Problem persisted with lower frequency for several days then disappeared completely for three weeks before reappearing daily last few days. Car travelled 2500km interstate trip last few weeks without tripping out, now temp guage trips out after a few minutes. Sometimes it will operate normally after restarting engine, other times it will trip almost immediately after restarting.

Auto electrician connected diagnostic scope to engine which verified that main computer correctly read engine coolant temp verified by infrared temperature reading near thermostat so problem seems to be one of the computers is not communicating to the other if I understood him correctly.

Would be very grateful if someone can point us in the right direction to resolve.