Some of the early Nissan OBD2 systems have dual diagnostic retrieve modes .
The diagnostic mod has a screw that can be turned to mode 1 for flash code ..
How they get it to you is the first 2 digits are long flash and the next 2 digit sequence is short flash..
so, the 0315 is mil light showing a flash code of 3 long flashes followed by 15 short.... the zero understood to complete 2 digits.....ie-03
This is prob only P codes...