p1643 Error code and engine stalling

[BlakeJ]

Hi all,
I bought my mk6 just under a year ago and within a month or so I experiences some troubles starting the van. The van would crank over and die a few times before starting up (in 20+ degrees). The van also randomly shuts off after 30sec - 3mins idle, it doesn't seem to struggle at all before stalling it just randomly dies. I took it into the mechanic and he decided the first step was to change the fuel filter. This helped substantially for a few months however it didn't solve all the symptoms. The van still wouldn't idle for long periods of time. Now the van has started to have these issues more regularly and will often stall when starting up. I had the codes read and error code p1643 is coming up - FPM circuit low voltage and cannot be cleared. I've also noticed my fuel consumption is getting worse, I just got back from a 1200km round trip entirely highway driving and sitting at 100kph I averaged 11.8 L/100km even after just cleaning the egr (not sure if this is related in any way to the fault code).

Details: Van is a 2004 mk6 vj bus with a diesel 2.4L engine
engine is the D2FA variant.
233,000km

Things done to the van in the last 6 months.
Fuel filter changed
New Alternator
New tensioner Pulley
New belt
As well as standard servicing, oil changes etc.
(Probably all irrelevant just trying to give as much information as possible).

I would really appreciate any help or advice on what to do next.
P.S I have searched everywhere for problems relating to p1643 and every one of them seems to be ASM related.