From rangerovers.net:
http://www.rangerovers.net/newrremedies.htm
Body ECM (BeCM) Problems
See also Alarm System problems above and BECM Operation, Diagnosis and Repair page.
Virtually all non-engine functions (and even enablement of engine cranking) on the new Range Rover, from the windows to the suspension, are either controlled or monitored by a computer known as the Body Electrical Control Module ("BeCM"). Its tentacles are omnipresent. This electronic "brain" is also the one that supplies most of the 150 possible messages to the vehicle's Message Center alerting the driver to all manner of vehicle functions and malfunctions. When all that wizardry is working according to plan, everything is bliss. However this expensive (about $1000) little box full of electronics and microprocessors is one of the few ECUs in modern vehicles that seems to have a solid reputation for failing. To be fair, at least some of the "failures" have been due to the operator not understanding the complex BeCM functions, and there has actually been nothing wrong. This is known to be the case where BeCMs have been replaced for supposedly malfunctioning reverse mirror dipping. Also, it should be said that most BeCM failures do not disable the vehicle, but result in minor annoyances such as lights turning on (or not turning on) etc. For these kind of p[roblems, if you have the time and inclination, with a modicum of electrical knowledge, there is a fair chance you can diagnose and fix the problem yourself. Full details of how to do this appear in the repair operation section on the BECM Operation, Diagnosis and Repair page.
Nonetheless, the BeCM has not acquired its Lucas-like reputation for nothing. One owner reports that "My 96 4.0 locked me out...... something to do with the BECM going into anti theft mode... So I am being told, no lights, no check engine light no sirens nada! I am able to open the car normally, the radio works, the windows etc.....It just won't start." The computer had gone mysteriously into theft mode. Fortunately in his case his mechanic (Larry at Four Oaks Garage in Santa Monica) was able to reset it in all of 5 minutes. No details are available on how he did it -- if you know how to do it, please write in!! (Update 2004: From bitter experrience we now know he may well have used the Emergency Key Access (EKA) procedure described under Alarm System problems above and in more detail on the the Key/Remote Problems page). Most cases I have heard of were not so easily resolved. I personally am aware of one vehicle that was disabled for weeks at a dealer while the BeCM was swapped and other steps were tried to figure out its problem, apparently another case of something to do with the alarm system deciding to prevent the engine from starting.
If this sort of prospect is alarming to you, make sure you buy that extended warranty plan!!
For more details, see the BECM Operation, Diagnosis and Repair page, the BeCM replacement/reprogramming page, and the Security/Alarm System Problems and Solutions page.
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From everything you've mentioned, I would pass on this vehicle. You're talking about a high-mileage rig with a complex management system, which makes engine or other swaps more difficult. Part costs and premium gas are two other downsides. Don't get me wrong, it's a capable vehicle, but you might consider other options if you want an expedition vehicle. Disco Is are my choice, if you can find a clean example.