Might be worth getting the codes looked at. Check an owners forum. If it's a diesel deffo get it checked.
My 10 year old Nissan throws the Engine Management light every so often. Only ever does is on dual carriageways/motorways at about 50-60 mph when cruising, or foot off the gas - weird. It runs fine, starts first time. I do have the reset procedure - Nissan kindly built in all sorts of re-set procedures into the software, which means you can tell the ECU to re-scan and reset certain systems without the specialist Nissan software - just a few presses of this and that etc.. Takes less than a minute to reset the Engine Management Light, switch on, wait 3 seconds, press the accellerator fast 5 times, wait 10 seconds, hold accellerator down for 12 seconds, release wait 10 seconds, down again for last 10 seconds then re-start - all clear.
I can only suspect an over sensitive sensor - there are 4 on the exhaust on the 1.8 petrol as this was one of the best selling variants, and it was the engine that Nissan used to keep the emission levels down so that the whole 'range' of cars came within the agreed levels.