I know this is an old-ish thread... and this may not be relevent, my cars a meriva 1.3 cdti (A13DTE engine)
i was getting the following fault codes recuring:
P0299 - Engine Underboost
P003A - Turbocharger Boost Control Position Not Learned
Also had an overboost one once, and car went into limp home mode a few times, always coming back with the P003A code.
Checked the turbo's variable vane lever, and it was stuck, i worked it up and down a few times (had to use a screwdriver to lever i first few times) then it free'd off and i could then move it by sucking on the vacuum pipe (poor mans mitty vac
I'd read that the car will do a boost control position calibration once per engine start, certain conditions like over a certain cooland temp and that, but after freeing my vanes off, the DTC went away and hasnt come back,
Ok i then got :
P2453 - Diesel Particulate Filter (DPF) Differential Pressure Sensor Circuit - High Temperature
This was the DPF pressure sample pipe spit, common thing aparantly, rubber hose off the short metal pipe on the DPF... was bound to go at some point, replaced with with some 8mm fuel pipe and been fine since.