well you need a repair manual to know the codes and I think its the check engine light that flashes on and off a number of times to see what is wrong, I think this is for obd 1 cars I dont know about obd 2 ? well I know this is how domestic cars did it I'm not sure about import, just phone the Nissan dealer and they wil probly tell you how to do it. Some one tell if im worng i lernd this a long long time ago.