Hi Peter
Don't worry about the electronics, much of the electronics you already have albeit in a different form. From the XM you have a hydroactive controler, this is now incorporated within the pump and the mechanical height correctors on the suspension have been replaced with relatively simpler pots and electrovalves. Anti-skid with which you will already be familiar has grown a bit into traction control and stability control, and if you have an HDI then the engine ECU won't be much different in a C5.The big difference is that the interconnection of the various devices instead of being done with lots of separate interconnecting bits of wire is done with just two wires.
IMHO the electronics themselves are very reliable, I strongly believe that most failures of electronic units on cars are due to people trying to troubleshoot problems without either the proper equipment or proper knowledge of what they are doing and that applies to the trade as much as DIYers.
You have already got the one piece of equipment you really need to identify and troubleshoot a C5, a Lexia all you need to do is to get it to work and learn how to use it,:-) the value of the Lexia is not so much that it will give you error codes it is that it will allow you to read and record in real time a wide variety of data from various sensors and systems.
I came to the C5 by way of XM's, and like you I was concerned about maintenance issues,I came to the conclusion that a Lexia was going to be essential to accurately diagnose problems on these cars so I factored the cost of one into the purchase budget.
I have had a Mk1 2.2 Exclusive SE for three years now, you can't get a C5 with more electronics than that.
In the three years I have had the car I have had a total of 7 electrical faults. Tyre pressure sensors, the batterys go flat after ten years, removed with the help of the Lexia. Alternator, brushes. Hydraulic pump, brushes / commutator corrosion. Secondhand pump purchased replacement unit built using original electronics as the ECU on the secondhand unit didn't support Xenon HIDS. Rear window locking due to failed switch, easily diagnosed with Lexia. Failed speedo, broken torque motor easy fix common problem. Radio, poor RF gain another radio. Auto gearbox hanging on to second gear.
Off all these failures only the radio was a failure of an electronic unit per se which required the unit to be changed, the gearbox problem was due to incorrect software options being set, easily resolved with the Lexia although diagnosis and elimination was a bit time consuming.
I regard the car as extremely reliable, 2.2's have a bad rep as regards reliability, totally undeserved in my opinion, and auto boxes seem to be a subject that cause strong opinions, however autoboxes don't suffer from DMF's falling apart, do suck fuel though
. None of the problems I have had are out of the way for a ten year old 100K plus car.
The only failures that I can envisage costing a lot to resolve are a failure of the Engine ECU or the BSI and this simply because they are coded to each other, in either case I suspect that one would have to buy new because of the requirement to have a "Virgin" unit to code.
Finally IMHO the C5 does not handle as well and is not as comfortable as the XM
cachaciero
but although I was an electronics engineer all my working life, they scare me witless, I grew up with valves and components you could see. I have seen quite a number for sale as spares or repair due to 'unrepairable' electronic problems, is this a fact or do the dealers just dont know what they are doing.
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) and also tpms or tyre pressure monitors, I would probably remove this, because at £50 per valve from GSF, it is an unnecessary annoyance.