The ECM in BMW vehicles has a built-in self diagnosis system which detects malfuntions in the system sensors and alerts the driver by illuminating the check engine light located in the instrument cluster.
The ECM stores the failure code until the diagnostic system is cleared by removing the negative battery cable for 5 seconds or longer. The warning light goes out automatically ( after five starts ) when the problem has been repaired.

Retreiving codes:
   There are 2 types of codes accessible on a BMW. The flash codes and trouble codes that can be retreived only with a BMW tester. We will focus on the codes that don't require a special BMW scan tool.

The check engine light should come on when the ignition switch is in the On position, when the engine is started the check engine light should go out. The light will remain on when the vehicle is running if the diagnostic system has detected a malfunction in the system.  To read the codes, turn the ignition switch to the On position but don't start the car, depress the accelerator pedal 5 times ( 6 times on 12 cylinder mdels ) within 5 seconds and wait for the stored trouble codes to be displayed.

The diagnostic code in BMW vehicles is the number f flashes indicated on the check engine light . If a malfunction has been detected, the light will blink the digits of the code, for example: on 1988 3-series models, code 3 will blink three flashes, followed by a pause of about 3 seconds followed by any other codes stored in the ECM.
On 1989 and later 3,5 and 7 series models, the codes will display as follows: let's say for instance a code 1223, ( coolant temperature sensor ) will flash the first digit ( one flash ) then pause, flash the second digit ( 2 flashes ) pause, flash the third digit ( 2 flashes again ), pause and flash the last digit ( 3 flashes ). Followed by another pause , if there are other trouble codes stored, the computer will display them in the same way, if there aren't any other codes, the ECM will repeat the previous code, once all the codes have been displayed, the check engine light will remain on.

Clearing the codes:
   Disconnect the negative battery cable for five seconds or longer. 

 TROUBLE CODES:

1988 3 Series:

Code             Probable cause

Code 1   Airflow meter or Mass Air Flow sensor ( MAF )

Code 2   Oxygen sensor

Code 3   Coolant temperature sensor

Code 4   TPS

 

  1989 and later 3, 5 and 7 Series:

Code               Probable cause

1000, 2000   End of diagnosis
1211, 2211   Electronic Control Unit ( ECU )
1215, 2215   Mass Air Flow sensor (MAF)
1216, 2216   Throttle Position Sensor
1221, 2221   Oxygen sensor
1222             Oxygen sensor control out of range
1222, 2222   Oxygen sensor regulation
1223, 2223   Coolant temperature sensor
1224, 2224   Intake air temperature sensor
1231, 2231   Battery voltage out of range
1232, 2232   Idle switch
1233, 2233   Wide open throttle switch
1251, 2251   Fuel injectors ( final stage 1 )
1252, 2252   Fuel injectors ( final stage 2 )
1253             Cylinder no. 3 fuel injector
1254             Cylinder no. 4 fuel injector
1255             Cylinder no. 5 fuel injector
1256             Cylinder no. 6 fuel injector
1261, 2261   Fuel pump relay
1262             Idle speed controller or idle air control valve
1263, 2263   EVAP canister heating relay
1264, 2264   Oxygen sensor heating relay
1444, 2444   No faults in memory.

NOTE: On 12 cylinder models, codes starting with 1 indicate problems on the right cylinder bank ( cylinders 1-6 ), codes starting with 2 indicate problems on the left cylinder bank ( cylinders 7 - 12 ).