Hi matey..where are your location? There might be few Zed specialist around your area. Nissan garages are called stealer for a reason..they charge exorbitant price on parts and labour and simple diagnostic work. Don't pay £190 for an O2 sensor..that's too much. PM our resident Zed specialists ZMANALEX or R35LEE, they will sort you out. Those two know a hell lot about the Zed. I am currently having the same problem with the check engine management light. It says the O2 sensor but I have replaced this and the mass air flow sensor...and the lights are still on. the error engine code might not necessary tells you which component/sensor needs changing. It can be other sensor or electrical parts. I am hoping i will get it sorted soon..it's a sick Zed at the moment Much as i enjoy driving it, it's still not right to be driving around with your engine mangement light constantly on. So i know what you mean. Have been told that They can be pain in the a**se to sort out if your car has ever been water damaged like mine. My car runs ok..not notice any different in fuel consumption either..touchwood.
btw.