fault codes on your ca18det 180SX / silvia ECU

Reading the fault codes on your 180SX ECUThe following instructions should allow you to easily read and/or erase trouble codes on your cars electronic control unit (ECU).The instructions come from a Nissan service manual. Most Nissan ECCS system cars from the late eighties on will be very similar to read as the 180SX/Silvia. The only difference is likely to be some of the actual fault codes and their descriptions.
In a few words, reading to code/s requires accessing the ECU, placing the unit in self diagnosis mode using a screw driver, andlooking at the flashing lamps on the unit to see what code is displayed.

1. Accessing the ECU
The ECU is located in the passenger side foot wells kick panel. You need to remove the two fasteners of the door sill in order to remove the kick panel. Two metal screws and a plastic fastener hold the kick panel. To remove the plastic fasteners, unscrew the center part and pull out the other part.
Under the panel you should now see the ECU with its connector and wiring loom feeding it. Unfortunately, you have to access the back side of the ECU facing the firewall. On an R30/31 Skyline it faces the right way.Unscrew the unit and turn it 180 degrees on the vertical axis without unplugging it. You may need to release or cut off the plastic clip that holds the loom to the lower mounting to get enough slack.
You should be now able to see the front of the unit. An adjustment screw (used as a switch) , a green inspection lamp and a red inspection lamp. The screw is also supposed to adjust the idle speed as well a select ECU modes but I've never seen any noticeable difference from turning the pot with the engine running.
MARK THE ORIGINAL POSITION OF THIS SCREW AS A PRECAUTION. UPON DIAGNOSTIC COMPLETION, RETURN THE SCREW TO THE PREVIOUS POSITION. OTHERWISE, ENGINE IDLE SPEED MAY CHANGE.

2. The ECU modes
The Electronic Control Unit has five modes:
Mode I- Exhaust gas sensor monitor (Normal mode)Mode II- Mixture ratio feedback control monitorMode III- Self diagnosticMode IV- Switch on/off diagnostic systemMode V- Real-time diagnostics system.
The unit automatically return to normal mode I when the ignition is switched off.
Troubles code are stored on mode III. The stored codes will be lost if the car battery isdisconnected or if after selecting mode III, mode IV is selected. Only mode III will explained in this text until I know more about the other modes.

3. Changing to mode III.
- Turn the ignition 'ON' , don't start the engine.- Turn the ECU adjusting screw fully clockwise.
The lamps will flash a number of times with a longer break between each string of flashes. E.G.The inspection lamps will flash once, the unit will be in mode I. The inspection lamps will then flash twice, the unit will be in mode II. The inspection lamps will flash 3 times, the unit will be in mode III. The unit will continually cycle through all five modes until the screw is turned back anti clockwise just after the needed mode flashes are done.
- Turn the screw back after the lamp has flashed 3 times.- You are now in self diagnostic mode III.

4. Reading the trouble codes.
The codes are indicated by the number of flashes on both red and green lamps. First the red lamp flashes and then the green one. The red lamp corresponds to units of ten and the green lamp to units of one. For example, when the red lamp flashes once and the green lamp flashes twice, this signifies the number "12". There may be more than one code, there is a long break between each set of red then green flashes to separate them if there is..
The codes are: Possible cause: Symptoms:11 Crank angle sensor circuit Wiring fault(connector), faulty sensor. No or difficult starts, bad idle.12 Mass Air flow meter circuit Wiring fault etc., sensor, ECU No or difficult start, lack of power.13 Engine temperature sensor circuit Wiring fault etc., sensor, ECU Engine stalls, lack of power, low economy14 Vehicle speed sensor circuit Wiring fault etc., sensor, ECU Lack of power, poor idle21 Ignition signal missing in primary coil Wiring fault etc., sensor, ECU No or difficult start, bad idle, misfires31 E.C.U. (E.C.C.S. control unit faulty) Wiring fault, ECU internals ?33* Exhaust gas O2 sensor circuit Wiring fault etc., sensor, ECU lack of power, low economy35* Exhaust gas temperature circuit Wiring fault etc., sensor, Cat/conv lack of power, low economy, dash lamp43 Throttle position sensor circuit Wiring fault etc., sensor, ECU lack of power, low economy, stalling45 Injector leak ? Wiring fault etc., sensor, ECU ?55 No malfunction ( all normal )
*unleaded models only.

There may be some more but I have not finished the list yet.
After the diagnostic codes are viewed, turn the ignition 'off' to return to mode I.
Then return the screw adjuster to roughly its original position OR half way if you forget where it was.

To erase the memory, use mode IV. The codes are automatically erased from memory when the starter is operated fifty times after the last trouble occurred.

source: http://forums.nicoclub.com/zerothread?id=270584