I don't own a diesel or anything to back this up.
BUT I can't believe your central locking/unlocking is controlled via your engine's mechanical vacuum pump.
Can you lock/unlock all doors with engine off?
If yes, than there must be a separate vacuum pump for this. Check under your rear seat, if there is one....it will be there.
You can get at the wires at the pump, pass kick panel, driver kick panel.