Intermittent limp mode from the outset

[jammy_c]

Hey Guys!

I've got a 2006 2.0 TDI Passat B6, It has a random fault that's been driving me crazy for the past 12 months and I can't get to the bottom of it!

When I switch the ignition on, there's about a 50% chance that the car will go into limp mode immediately (before starting the engine) Engine light on exclamation mark on the dash screen plus a "ding" warning sound, then when it starts the engine won't rev past 3000 RPM. Then after restarting 2, 3, maybe 4 times it will allow the engine to rev fine again, but will still show the exclamation and everything seems to work with the exception of the cruise control. It will stay like this then for the rest of the journey, but the next time i go to use the car it is completely fine.

It's a total lottery as to whether it will work properly or not.

Fault codes thrown up are:

*Altitude Sensor Short Circuit to B+
*Cylinder 3 pump/injector valve Short Circuit to B+
*Cylinder 1 pump/injector valve Short Circuit to B+
*Mass Air Flow Circuit Short Circuit to B+
*Turbo Charger Overboost Control Short Circuit to B+

It sounds to me like it's an electrical issue as they all come up at the same time and complain of power circuit issues.
So far i've removed, cleaned and re-attached the earth points in the engine bay and replaced the two ignition relays, to no avail. I also changed the boost sensor and the cleaned out the EGR as that is what the local garage suggested, but no improvement.

The issue went away totally for about a month when I replaced the battery in December and I thought I'd cracked it! but now it's returned. That can't just be a coincidence, can it?

Also... the red/black dash display intermittently keeps fading in and out from the left. sometimes it's perfect for a whole journey, sometimes it's barely readable. doesn't seem to have any correlation occurring alongside the other fault though.

Any Ideas guys?

Any suggestions are much appreciated.

Regards
James.