Glowplug warning P0674

[Taxiboy]

Well I still have my awful Passat 2.0tdi 150. This car still runs crap unless it’s on active DPF regen where the car runs great then after it completes it runs rubbish/noisy again. My usual garage few months back checked everything out said the car was fine and drove brand new so seen nothing wrong. Told me any bad sensor (O2 or MAF) would show a code. Decided to take it to a diesel specialist with a very good reputation with a costly diagnose fee. Explained my issues and once car was checked they found nothing wrong with it they said it drove well. When i drove off with the car from them it drove well but next day was rubbish again.
Over the past few weeks with the air con on rattling appears to come from the alternator belt but at times car will drive better. Went out today but drove with the windows down. The car sounded horrendous with constant diesel knock/spluttering the whole time aswell as deep exhaust noise too.
Went back out an hour of so later and decided to scan to see if anything showed up. I have nothing showing on dashboard and I got pending code P0674- Cylinder 4 Glow Plug Circuit/Open. Does anybody know if this could be a bad glow plug that now needs replaced?
Appreciate any help or opinions.

[VAG-Abound]

Deleted, and moved to correct thread.