Piston rings getting gummed up with carbon is a known Purecrap issue causing high oil consumption.

Citroen main dealer will be reluctant to find anything while the car is under 6 years old in case Citroen UK then has to dip in to its goodwill fund to repair it.

Stellantis are really taking a big hit at the moment on goodwill repairs for older failed Purecrap equipped vehicles.

I find it hard to believe a Citroen main dealer with Diagbox can't read the code. If there's a light on then a code is logged in the BSI and engine ECU.

Maybe get a second opinion from someone local with the equipment. Google "planet owners map" to find a fellow Pug or Citroen owner with a clone of their diagnostic equipment.

...and probably damage to the engine, as I think it may be one of the last of the ones which had crumbly cambelts fitted which caused expensive problems. I do not expect to have to add any oil before I next change it 10,000 miles after the last change.

Might be time to adjust those expectations

Main risk is the belt breaking, or clogging the strainer with bits, quite a lot worse than a bit of excess oil use.

I'd probably want to have a look, either removing the sump or with a fibre-optic camera.

Paper chromatography of oil for debris detection is easy, though not so easy to interpret. Oil pressure gauge other way around.

If rings are stuck, piston soak might be worth a try (or a few tries). Lots of possible solvents, but I might try brake fluid, which is a good carb cleaner.

Probably worth changing the oil afterwards, esp if you use brake fluid.

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