Posted this for general info - Had a strange problem with temp gauge acting erratic and engine note changing then the MIL would appear/disappear. Not good when you are in the middle of no-where at 3-00AM. Kept coming and going. Stopped and turned off ignition - waited 5 mins restarted alls well :
Next day Used scanner and found engine high temp , but no follow-up? went through all the hoses, levels, plugs etc and found nothing.
So put it down to the ''Jaguar Gremlins''. Couple of days later - similar thing happened - Started to panic
Scanner out again - same news? Sudden thought - went into onboard IDS and found (amongst others) temp gauge code F4 (but this kept changing?) = open circuit +shorts between wiring temp sensor and ECM. Eventually found bad/suspect connection on terminal plug.
This was 400 miles ago - seems all okay now. so maybe it was the fix - or I knocked a gremlin off its perch as I rummaged around
I am not very competent around this on-board IDS - Have I followed the correct path - or just been lucky?? I have doubts as my scanner was not totally in agreement

 

It sounds like your scanner DID show you the issue, as had your temp gauge.

However, you (probably not being a car tech - and fair enough at that!) didn't realise what the implications of the data were. (Now you do LOL)

The various sensors in OBD are critical to the car's running. That's why they're part of OBD.