AUDI A6 2.7TDI sline 2008 Avant

I have an odd issue. I have run a diagnostics on my car and get the below error code (engine light comes on). Initial thought was the manifold motor had died. So a few months ago I changed the lever arms on manifold, seemed to fix issue for a few days till I refueled car. So I left the error for a bit.
Last week I swapped the manifold around (driver side to passenger vice versa), Reset the DTC code, restarted car and engine light went off-:-). refueled car, immediately after I started the car and the engine light came on !
I'm confused as to what the fuel cap has to do with the engine management light coming on.
So now I am stuck as to what the cause is, I don't want to start replacing manifold motors, flaps etc if the issue is to do with something else.

I would really appreciate guidance on this! :-(

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Address 01: Engine Labels: Redir Fail!
Part No SW: 4F5 910 401 Q
Component: 2.7L V6TDI G000CG 0020

1 Fault Found:
004120 - Intake Manifold Runner (Bank 2)
P1018 - 001 - Lower limit not reached
Freeze Frame:
Fault Status: 01100001
Fault Priority: 0
Fault Frequency: 1
Mileage: 165345 km
Time Indication: 0
Date: 2017.01.15
Time: 11:16:54

Freeze Frame:
RPM: 0 /min
Torque: 0.0 Nm
Speed: 0.0 km/h
Voltage: 11.70 V
Duty Cycle: 20.5 %
Duty Cycle: 88.8 %
Duty Cycle: 20.5 %
Readiness: 0 0 1 1 1

Thanks,
PC