Update. I've been ill.
Firstly apologies, the last code, was P1351 glow plugs.
With code P0238, once erased, this has not returned, yet. Live data indicates correct boost pressures. I suspect the turbocarger vanes may stick occasionally, and possibly seeing overbooost, the vehicle goes into limp mode. The actuating arm does not appear to be sticking when operated with a Mityvac. Vehicle performance on road test is normal.
The code that resets instantly is P1445. Using live data we can see that the fuel cap switch is operating normally. The data shows:
Additive min. level not reached.
Total quantity of additive injected into PEF 106gr
Total quantity of additive injected from the additive reservoir 37 gr.
The Engine control unit shows 106gr of additive in the PEF and a volume of 3000ml in the additive reservoir.
There is a disparity in these figures, but I've never seen a set of figures from a known 'good' vehicle. There aren't any codes stored in the additive control unit. We have absolutely no service history for the vehicle.