The front of the ECU has 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.
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 monitor
Mode III- Self diagnostic
Mode IV- Switch on/off diagnostic system
Mode 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 is
disconnected 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 economy
14 Vehicle speed sensor circuit Wiring fault etc., sensor, ECU Lack of power, poor idle
21 Ignition signal missing in primary coil Wiring fault etc., sensor, ECU No or difficult start, bad idle, misfires
31 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 economy
34 Knock sensor
35* Exhaust gas temperature circuit Wiring fault etc., sensor, Cat/conv lack of power, low economy, dash lamp
43 Throttle position sensor circuit Wiring fault etc., sensor, ECU lack of power, low economy, stalling
45 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.
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