The codes are in memory
If one or more fault codes are detected, use the fault code table at the end of the chapter to determine their meaning.
If there are multiple codes, check for a general fault such as a ground or voltage circuit fault.
If any engine management system related components or circuits need to be tested, refer to the component testing procedures described earlier.
Once the problem has been corrected, clear the codes and operate the engine under various conditions to determine if the problem has been corrected.
Check the ECU for fault codes again. If codes are still stored, repeat the above procedures. No codes in memory.
When there are problems during engine operation, but there are no fault codes in the memory, then the fault is outside the parameters provided by the design of the self-diagnostic system.
If the problem is related to a specific component, refer to the chapter that describes the testing procedures for most of the components and circuits related to the engine management system.
Information taken from this resource: «bmwman.ru»