Re: Weird Problem???
I've been struggling with exactly this problem for a few months now.
It first happened at the beginning of 2012, and I noticed a cracked connector on the coolant temp sensor. Replaced this and all was OK for about 6 months.
It went again Nov 2012, so I replaced the coolant sensor again, but it did no good.
The received wisdom is that it is a duff signal on the PCI bus wire, possibly due to a dodgy earth connection somewhere. The most likely location being in the loom between the door(s) and the body.
Good luck with this, my latest thought is that it is my Fuel Level Sensor, I get erratic readings on the fuel gauge.
A temporary fix is to either remove and replace the IOD fuse, (No. 15) in the under bonnet power distribution, or disconnect, and re-connect, the battery negative. Either of these resets the BCM and your readings will then be OK, but for how long is anybody's guess. Make sure you know your radio code before you do this.
I'll be interested to hear how you get on.