EVIC display failure solved - I hope!
after months of chasing this stupid failure, jumping in and out of the vehicle to disconnect the battery/remove and replace the IOD fuse I think I've finally solved the problem.
The solution started with the old favourite, 'broken blend door(s)'. I was getting cold air from the heater on my side (RHD) and my wife was getting warm(ish) air. Cut my way in to the blend doors, as per 'JGCParts' instructions. Got as far as the the first (driver's) and found it was broken. The passenger one was O.K. Rang up the 'stealership' to get a single replacement blend door and was told "We don't do those any more because they are prone to breakage. There is now a modifying kit comprising 2 metal doors and spindle." I wonder where they got that idea from? Cost was just over £100 ($150). I thought "....sod that....", took out the broken parts and repaired the door. Cost - half a dozen pop rivets and a little time and effort. Result - working heater, but not very warm.
Engine was only getting to about 60 deg C (140F). Must be the thermostat. Bought a replacement part, Merc Sprinter NOT Jeep. When I got the old one out I found that plastic part of the temperature sensor was cracked. Replaced that as well. Now we have a fully working heater, engine runs at 85 deg C (185F), which is more or less what it should be.
Where does the EVIC/BCM/ECM/TCM/whatever figure in this? Well, I reckon the dodgy temperature sensor must have been sending duffy signals to its control module and sending the system down, because, ever since I did the aforementioned jobs everything has been functioning perfectly. At the time of writing this I've done just over 110 urban miles, with numerous stops and restarts and the system hasn't dropped out once.
What is they cry in the deep south "Yee-hah!". Just hope I've not just jinxed it.
If anyone's interested in the details of the repair of the blend door(s) on a 2.7 CRD Grand Cherokee, it may be applicable to other models, I'll do a seperate post on it.