Hi Jono.
The variable valve timing uses a hydraulically adjustable cam sprocket. The cam timing (ie the advance or delay from the base timing) is adjusted by pumping engine oil into this "VVT unit", and this is done by the engine computer rapidly cycling the solenoid off and on so that engine oil from the oil pump is added or drained from the VVT unit constantly. The timing codes (P0026 etc) mean that the engine is wanting XX degrees adjustment and is cycling the solenoid to try and adjust the hydraulic flow, but is not measuring the timing it wants on the cam position sensor.
That's why the root issue could be the base oil pressure, the solenoid being faulty (or having a clogged filter screen), the solenoid wiring or fuse being faulty, the cam phaser (VVT unit) being faulty or blocked, or the cam position sensor being faulty (the trigger being loose or the sensor air gap being too large, for example.)
Long oil change intervals suggested by the factory don't help. If the oil used by previous garages is the cheapest junk they can buy in bulk, and changed at 15,000km plus or minus 5000km depending on the owner, then the sludge accumulated in the oil will clog the screen, solenoid or phaser. The cheapest starting point is possibly changing the engine oil to a good quality (slightly thicker) grade including a good engine oil flush product, and see if the desludge process helps. Then, it's a matter of going from easiest to access (eg solenoid, cam sensor) to hardest to deal with (timing belt, cam phaser). Having an oscilloscope to see the output from the cam sensor would be helpful, but even most garages don't have this…
