I would also be trying to clear the p0380 fault code before looking for anything else, ( obviously when you fix that problem and the car still has a another problem the customer will get annoyed with you and tell you that the glow plugs have nothing to do with it and your looking for the wrong problem and you don't know what your doing )

I have had a few of these in with glow plug problems and if all 4 glow plugs or or anything on that circuit is Open circuit then it will go into limp home mode.

The Code description on Lexia that I was getting was something like "Glow plugs controlled but not supplied".

Have you checked the glow plug relay and wiring to it. ?

I have fixed some by swapping the relay, But I had one that had been fitted with a second hand ecu kit by another garage and it was permanently in limp mode and wouldn't rev up properly, The Garage that did it also swapped the relay but it didn't cure it, I checked all the wiring back to the ecu and it all checked out ok So after trying another relay I suspected a Faulty ecu or the car that the Ecu was off used a different type of relay. ?? On that one I bodged a warning light into one of the control wires and it came out of limp mode and drove fine, The Customer was Happy to try it at that and it has never returned, so i assume that its still running ok. OR he's sold it.

H.T.H Tony.