Failsafe mode for a 2005 diesel x5

[bannon]

I bought my used x5d 2005 in october last year and all was fine. About a couple of months ago I was coming home from a 2 hour journey and whilst driving around 40mph i was getting onto a motorway and put my foot down to pass a slower vehicle. it was at that point that the car went into trans failsafe mode and i was left in 3rd gear. I pulled over quickly and turned off the engine. within 2 minutes i restarted the car and the fault disappeared and i got home only for the fault to happen again. the next day i drove the x5 and was careful not to push it too much when overtaking or starting from a stop position.

The car was ok for a few weeks but happened again on my way home from another 2 hour journey. This time the fault code would not disappear.

I took it to my local mechanic who couldn't find any major fault codes and reset the system.

It has been driving ok although after a short journey the trans failsafe mode came up and I cleared it ageing by turning off the car for 2 mins.

can anyone tell me what is the best thing to do to try and rectify this issue?

Thanks
Bannon

[X5Sport]

[quote="bannon"]
I took it to my local mechanic who couldn't find any major fault codes and reset the system
[/quote]

What faults did show up, and did he read the gearbox fault memory?  It could be a simple sensor issue, bad battery or something more serious.

If your mechanic has access to Autologic (Bosch Autocentres tend to have it) then it's worth getting it rechecked.  If not then find someone with the system.  Alternately get your local BMW Dealer to do a fault code readout.  There ought to be a record of it going into limp mode and why stored on board.

Oh, and 

Richard

[iff26]

Maybe too late to reply but I had 100% same issue! Nothing seems to be wrong but there is!
I can put money on that its alternator or battery! Main played 6 weeks like that and then alternator just gave up!
Should read out power supply and generator faults!
Hope you have sorted it already but if not prepare 1 hour labour and £350 for alternator unless it's Water- cooled!