We may need more info about the car - which engine, particularly? My 200ZR, for example, does not self-diagnose in the manner of a normal Z31, but has to be treated as if it is a 200SX of S13 variety. There are five separate diagnostic modes available of which Mode 3 is the most useful and will provide standard diagnostic codes once selected. Briefly:
Dismount ECU but don't unplug - so you can see the LEDs. Warm engine up if possible.
Turn diagnostic mode selector fully clockwise and watch flashes of the LEDs. When you see a group of three flashes, turn diagnostic mode selector back fully anti-clockwise. ECU is now in Mode 3 and may show one or more of the following codes in a cycling sequence:
11 (one red flash, one green flash): crank angle sensor
12 (one red, two green): air flow meter
13 (one red, three green): engine temperature sensor
21 (two red, one green): ignition signal
34 (three red, four green): detonation sensor
43 (four red, three green): throttle sensor
55 (five red, five green): all normal operation
Modes 1 and 2 can be used to monitor mixture ratio in catalyst equipped cars. (not used in non-CAT models).
Mode 4 can be used to monitor switching by idle switch, ignition switch and operation of the vehicle speed sensor.
Mode 5 can be used to measure momentary malfunctions in crank angle sensor, air flow meter and ignition signal - useful if fault is intermittent and not triggering a fault code in Mode 3.
