Friday evening the old XJR was driving superbly until I parked her. Saturday afternoon however, when I went to start her, she idled at 400 rpm and promptly stalled when I pressed the accelerator peddle. Restarted and the same thing happened, but this time was accompanied by beeping and Er on the climate control display, tried again for a third time with the same result. Cue lots of head scratching. Did not have time to investigate further over the weekend, so left the old girl parked up. Monday evening, plug in the cheap Bluetooth OBD2 code reader and pull codes P0116 engine coolant temperature circuit range/performance problem, and P0117 engine coolant temperature circuit low input. Open the bonnet and the grey plug on the temperature sender unit had come off, on examination the tang that holds it on is broken. Wedge it on until I can source a new plug and all is well with the XJR again. The bit that threw me was the lack of CEL or restricted performance warning, but the air con display beeping and showing Er ?

 

I have the beeping and error message on the display but that is down to the ambient air temp sensor on the front of the car being buggered..... I have disconnected the engine temp sensor many times without affecting the air con..... That is a strange one!

 

I am sure the Ac uses water temp to decide when to put the heater fan on.
On cold mornings the fan is very low until the water temp starts to rise.

No point blowing cold at the driver!

 

After reading your comment and the one from avt007, just went out to the car and pulled off the temp sender plug and tried to start the car... same thing, sort of idles at just under 400 rpm and dies when I press the throttle, and the air con beeping and showing ER. I will admit I am more baffled that it do not throw a restricted performance or CEL warning, yet tells me the air con has a fault ???
Maybe its to do with Jaguar customer service, they want me to be comfortable waiting for the tow truck ? lol

 

At least you have discovered a sure fire signal that the temp sender might be buggered. Now, if only the temperature gauge was fully functional we'd be all set!

 

Now there is a good reason to pick my name out of the hat for the RealGauge prize draw. lol