Landy's are expensive models.

You will get your solution and all info on service info,
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it's a very good website for vehicle problems even as old as 1991 ford..

you should checkout this website www.reliable-store.com that has books on all vehicles, name it they have it.

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I have ford expedition and I keep servicing and when needed repair it on my own. worth it !!!

Hi welcome main problems are the abs valves causing the 3 dash lights (search 3 amigos online) a really badly sited compressor can cause air suspension models to fail giving the bags a slow leak the V8 is a solid engine but can have radiator expansion tank and cap failures
the other issue is electrics windows and door looms are problematic

Dont have a definitive answer for you as the generality of it is along the lines of presenting a cup of ocean water and asking from which tributary around the world it came. I will attempt to answer it based upon pure speculation. Hope it helps...
What you are referring to is actually the BeCM or Body electrical Control Module. This module controls power to, grounding of, signals of operation to/from, and diagnostic info for every component in the vehicle which relies on power to function. Everything. It is the brain of all that is power in your rover. Nothing less than amazing actually, this unit is performing hundreds of operations at any given moment you are driving and even when your car is garaged and keys in your pocket. Each Land Rover is fitted to your vehicle, synchronized, and coded at the factory for your specific vehicle. While many systems are generic in nature there are systems such as perimeter alarm sensors and engine immobiliser which have unique security codes paired to the BeCM. Replacement of the unit can be done but it is not "plug & play" so if you or your shop performed the installation it was not completed in that the unit must be paired with the numerous sub-control modules by way of recoding. This function can only be done with the Land Rover proprietary diagnostic system called TestBook. A very few independants have this technology as its expense, around $30K keeps it out of reach and maintains the umbilical cord to your local dealers service dept.
It sounds to me like your BeCM went to work after install and sent proper signals out to various components however as the diagnostic data flowed back in it was received as encrypted garble. As the unit scrambled to interpret and process data it simply became scatter brained.
I beleive that the sync requires your Discivery be on site to perform, however you may check with a reputable Rover dedicated online supplier such as Roverland parts and ask them.
As to your Rover dealer, there must have been some level of communication breakdown because i cant imagine them not knowing the process or attempting to sell you a BeCM you didnt need.
Best of luck, sorry its not a quick fix answer. Feel free to repost any additional info or message my box directly and i will do my best to catch it and assist further.

I have friends running Freelanders. Some have spent virtually nothing on repairs and others have spent a fortune. Very hard vehicle to call. Look at Edmunds reviews perhaps. Is the previous owner available to recount his/her experiences? Some people (not a lot but Land Rover owners more than most) keep records of such things.