Here is a brief description on resetting your ECU.    

Firstly See if your car will benefit from a reset:

Pre MY99 - Reset required

MY99-00 - ECU adapts itself after a few miles (around 30)

MY01 - ECU works in real time constantly adjusting timing so resets

not required

How to re-set your ECU unit.

ECU clear memory procedure is as follows:

    1.   With engine at operating temperature, turn engine off and place gear shift lever into 

    park (auto transmission cars).

2.   Locate the two ECU check connectors, for most cars they are located under the

    steering column and consist of a black plastic male and female connector, and a green male & female connector. The exact location of the connectors varies with the different year models, but generally they are located under the steering column on the drivers side. With the ignition OFF connect black to black and green to green.

3.   Turn on ignition and cycle the gearshift lever from park to neutral and back to park

    (auto transmission), depress the accelerator pedal to full throttle and hold for a few seconds, and then release. Start engine and then drive for at least one minute, keeping road speed above 11 Km/h.

4.   ECU is now re-set.

5.   At this point the check engine light should start to flash the all clear signal (steady 1/2

    second interval flashes). If the check engine light does not flash, or indicates some other sequence, there is a fault present in the system, and should be professionally checked for necessary repairs.

    You disconnect the plugs AFTER the drive. You only need to keep driving until the check  engine light starts flashing (once every half second). 

ECU Reset by Disconnecting the Battery

Fill the tank with your normal grade of fuel, either unleaded(95 RON) or super unleaded (98 RON), hopefully choosing a good source,( bad petrol will defeat the object of an ecu reset), and drive 10 - 20 miles (more if possible) to ensure that the good fuel has refreshed all the parts it should do.

 1.  Park up  and unplug the battery, thus killing the power to every system on the car,

  including the Engine management system.

2.  Wait about 1/2 hour to 1 hour before re-connecting. The ECU will be forced to reset to

    factory defaults and on detecting the 95/98 RON fuel, give you better performance once you have given it a drive out to get the fuel registered. Obviously, if you switch back to bad petrol the ECU will reducing the timing to compensate but providing you listen to the car and change gear as you drop out of the power zone and not at the red line, you should be able to have optimum performance.

3.  One word of warning, putting the car under serious load while doing this won't work.

    This process, will indeed put maximum load on the engine, and is therefore likely to lead to knocking and hence the ECU will REDUCE the performance.

ECU Diagnosis 

1.  Locate the two ECU check connectors, for most cars they are located under the

  steering column and consist of a black plastic male and female connector, and a green male female connector. The exact location of the connectors varies with the different year models, but generally they are located under the steering column on the drivers side.

NOTE: sometimes they are still taped over with some small amount of plastic tape, so look hard, they will be there!

2.  With the ignition OFF connect the black male/female plugs together only. (The green

    connectors are only required for the ECU reset)

3.   Turn on the ignition. Do not start the engine.

4.   Turn on the ignition. Do not start the engine.

5.  The check engine light will flash. If it is a constant flash 0.5 seconds apart then there is

  no problem present. If it is any other sequence check the number of flashes with the codes below: 

    a 1.3 second delay between flashes = 10

    a 0.2 second delay between flashes = 1

7.   Once finished turn off the ignition and disconnect the black connectors. 

    List of Sensors

11 CRANKSHAFT POSITION SENSOR

12 STARTER SWITCH -  Starter switch is abnormal

13 CAMSHAFT POSITION SENSOR

21 ENGINE COOLANT TEMPERATURE SENSOR

22 KNOCK SENSOR

23 MASS AIR FLOW SENSOR

24 IDLE AIR CONTROL SOLENOID

31 THROTTLE POSITION SENSOR

32 OXYGEN SENSOR

33 VEHICLE SPEED SENSOR 2

35 PURGE CONTROL SOLENOID VALVE

42 IDLE SWITCH

44 WASTEGATE CONTROL SOLENOID VALVE

45 PRESSURE SENSOR/PRESSURE EXCHANGE SOLENOID VALVE

51 NEUTRAL POSITION SWITCH (AT Only)

51 NEUTRAL SWITCH LINE

54 ABNORMAL INLET LINE

61 INLET CONTROL SOLENOID LINE

62 EXHAUST CONTROL SOLENOID LINE (NEGATIVE PRESSURE)

63 RELIEF SOLENOID 2 LINES

64 RELIEF SOLENOID 1 LINE

65 DIFFERENTIAL PRESSURE LINE

66 TWIN TURBO SYSTEM

67 EXHAUST CONTROL SOLENOID (POSITIVE PRESSURE) LINE

68 EXHAUST VALVE DUTY SOLENOID LINE

85 CHARGING LINE

87 VARIABLE INLET SOLENOID LINE

89 AVCS SYSTEM

91 TCS RELIEF VALVE LINE

So if the Check engines flashes twice with an interval of 1.3 seconds and then flashes once with an interval of 0.2 seconds this equals 21 which is the Engine Coolant Temperature Sensor failing. 

    i.e. 2 x 1.3 sec flashes & 1 x 0.2 second flash = 21 - Coolant sensor.

    1 x 1.3 = 10 therefore 2 x 1.3 = 20 ,  1x 0.2 = 1 therefore 10 + 10 + 1 = 21