A6 2.5tdi died, suddenly and without warning

Finally got round to replaceing fuel return pipes at the weekend. Ran the car for 15mins static to check no leaks and went for a quick spin. Within 100yds zonk, nothing. Dead as the Norwegian Blue Parrot. Got it back home and checked the following; car spins over but wont attempt to start.
-Fuel in filter..............yes
-Fuel at injector........yes
-Cracked off injector nipples and no fuel seems to come out
-Can't seem to hear the fuel pump buzzing (this is what's bothering me the most)
-Relay clicking (under steering wheel panel) can hear and feel (removed and checked and is working (relay 4)

Just got VAG diag tool plugged it in and it pulled up these faults
(I don't understand the hexcode)
Engine;
1) 00542 -158 Needle lift sensor G80 KWP1281 (?)
2) 00575 -136 Intake manifold pressure KWP 1281
3) 01376 -165 Engine speed signal defective
Auto HVAC;
1) 01206 -027 Signal for duration of ignition:OFF

Does anyone think any of the above would cause non-starting and shed light on the coding.
Any help really appreciated as I'm fed up with trains already!
Regards
Kevin

adamss24 said:

The v6 tdi engine will start even without a working crank sensor, it will put on the coil lamp/warning light on the dash but will run albeit lumpy. If you get that code then i would replace crank sensor and check if the pump control unit gets power from ecu- measuring blocks 18, both fields should have 12 volts. I will try to delete the fault codes and see what comes back. Also a faulty needle lift sensor will not hinder the engine to start but will also be in some sort of limp mode- about 75% of total power will be available...

Click to expand...

So thanks for your replies.
Where do i find the engine crank sensor? I want to get a part number if i can

I think ive found it.......... right side of engine block under exhaust etc. No idea how i'm supposed to un-bolt it. measured the resistance of the sensor and it looks to be 100 ohms so i think it may be OK, does that point me toward injector pump rebuild??!£££

Just to clarify what I originally did was to replace ONE fuel return pipe on the right bank between the middle cylinder. It was seeping diesel enough to warrant attention. I give up on trying to undo the bolt holding the engine speed sensor in, is it actually possible? Bizarrely I can find no reference to how to remove it (G28) in the service manual either!? Sorry to go on but I'm running out of options.