High emissions help

Hi guys, getting some conflicting info reguarding this error.
Truck is 2011 scania G420 (no adblue). Currently on limited power, (very limited) and emissions high.
One guy plugged it in and says its nox sensor
Another guy plugged it in and says its turbo.
Called local parts distributor to price nox sensor and gave him the reg no. and he says its not coming up thst there are nox sensors on it.
Are nox sensors only on adblue?
Any advice would be greatly appreciated.