Just found this...
How to clear the fault codes from your 1994 on Nissan.
Its pretty easy really! When the management light is on it means your cars ECU has recorded a fault with something. You can access these using the method below. This guide covers all Nissans made between 1994 and 1999. If you have a Pre 1994 Nissan I have written a guide for them (and many other Japanese cars) too. Check it out my other guides to read it! If your Nissan was made after 1999 you need a fault code reader as these use the EOBD system. This method will work on Micra (K11), Sunny/Pulsar (N14) Primera (P10 and W10), 200SX (S14) and 300ZX (Z32) It should work on imports too providing they have the same plug and terminals.
Anyway, here is how it is done...
1. Find the data link plug. It is in the fuse box inside the car. When you look inside you will see a white plug at the bottom of the fuse box. Identify terminals 6 and 7 as in the picture below.
2. Turn the ignition on. You don't need to start it up but make sure your radio and anything you don't need running is off.
3. Connect terminals 6 and 7 together for 2 seconds then disconnect them again. 7 is an ignition live so don't touch it against anything other than terminal 6 or you will blow fuses and might damage the ECU which isn't cheap!
4. Count the times the management ligh flashes. A long flash means 10 and a quick flash is one.
5. If you lose count or think you may have missed a flash turn the ignition off wait a few minutes then start again at step 2 and pay attention this time!
6. You now have your fault code. Compare it against the list below.
Code Fault
11 Camshaft or crankshaft sensor (Common on early 2 litre Primeras)
12 Mass airflow sensor (Common and expensive on K11 Micras!)
13 Coolant temp sensor
21 Ignition signal (Used to be a common one on K11 Micras but most were fixed under warranty)
28 Engine coolant blower motor
34 Knock sensor
41 Intake air temperature sensor (Common on cars with aftermarket foam air filters, K&N/Accel type are ok)
43 Throttle position sensor
44 No faults
55 No faults
Should you get any code that isn't listed, try again. If the same happens you will have to take it to Nissan. Don't automatically assume the item indicated by the fault code is the cause. Check the wiring, connections and battery connections before jumping in.
If you can't get the hang of watching the management light, your cars dash has been removed or you have problems paying attention (Yes, like you, Stevie!) you can use the LED on the side of the ECU instead. It is on the side of the ECU (Usualy located under the dash in the middle) See the pic below...
Assuming you have fixed the problems you should now clear the codes. To do this you need to...
1. Turn the ignition on
2. Bridge terminals 6 and 7 again for 2 seconds then disconnect.
3. The management light should flash to say OK.
4. Bridge 6 and 7 again for 2 seconds then disconnect.
5. Switch the ignition off.
6. Turn the ignition back on and check for fault codes again. If you have fixed it you should get code 44 or 55. If not, get the toolbox again!
And thats all there is too it! No magic wand, no sacraficing goats etc.
From here.Hope that helps.