BMW Charging system malfunction – possible cause and repair case

The fault we are going to discuss today is the charging system malfunction, which is still described with real cases.

Vehicle information

Model: BMW 520Li

Year: 2010

Chassis: E60

Engine: N46


Fault symptom:

After starting the vehicle, the red battery light in the dash is on, and the CID displays "charging system malfunction!" It showed up three times in two days, and disappeared after a period of time.


Possible causes:

Generator does not generate electricity

Problem with wiring from generator to battery

IBS sensor is defective


Repair process:

1. Refer manual, the generator circuit diagram is mainly composed of several parts such as generator, IBS, DME, starter and so on. The fault code reported by the generator also has a clear direction, and the generator can still generate electricity when the BSD line is disconnected.

2. When the symptom persists, this situation is the best way to judge the failure point. First test the positive line. at this time, the generator does not generate power, and the voltage is 11.8V (abnormal).Then check that the BSD signal line voltage of the generator is 8.6V (normal). It is almost certain that the internal fault of the generator.

3. As we continued, the symptom disappeared, the generator was working normally after several times drive test, also the BSD. Is it possible that the DME occasionally has abnormal BSD control signals or there is a fault in the generator, which is only occasional happen?

4. After measuring the BSD waveform many times, all the result is normal. So we decide to replace the generator.

5. After replacing the generator, the owner drove the car for 3 months without charging system malfunction. The cause is generator failure.


DISCLAIMER: The technology and software in the blog are only used for technical research and auto repair, and are not allowed to be used for illegal purposes, We will not be responsable for any direct and indirect damages from the use of the file created by this page.