Trouble code memory (BMW 5 Series E39)

The control unit electronics detect faults in the injection and ignition systems, such as defective sensors, plug connectors or leaks (unreliability of contacts). At the first detection, these faults are entered into the fault code memory. At the same time, the engine status indicator on the instrument panel lights up, indicating that the fault code has been entered into the memory. If the fault occurs only once, for example, as a result of an unreliable contact, the indicator goes out, but the fault code is saved in the memory. In addition, data is stored that allows you to obtain information about the frequency of occurrence of the fault. At a BMW service station, using a diagnostic device connected to the diagnostic connector (on the right in the engine compartment) the stored fault codes are read and the faults are then eliminated.

If the engine or injection system starts to work imperfectly, the first thing to do is to read the contents of the fault code memory. To print out the fault codes, an electronic reading device is connected to the car at the service station.

All versions of the DME system have the ability to retain service functions: if sensors fail, the control unit relies on the average values of the accumulated values for the relevant sensors. If the volumetric or mass air flow meter fails, the control unit uses the throttle position and engine speed as reference values. This adjustment is automatic and the driver is not informed about it. The journey can continue, since the vehicle's driving characteristics are impaired only slightly. However, any faults that occur are recognised by the control unit and stored as codes. It is therefore advisable to visit a BMW service station and have the contents of the fault code memory read out, even if there are no obvious faults, for example during regular emissions testing.

Caution: When the battery is disconnected or the multi-pin connector of the control unit is disconnected, all accumulated fault codes are erased.

The article text was copied from an online resource: «BMWMAN.RU»