There are many reasons can cause car won’t start, and fault “increased battery discharge” is one reason, a high level of battery discharge can result in exhaustion of battery, further make the car won’t start. Below is a case with exact same fault and symptom, check how we diagnose and fix it.


Vehicle information

Model: BMW 523Li

Year: 2012


Fault symptom

The vehicle won’t start after it was parked overnight. The door could not be unlocked by remote control. After opening the door with a mechanical key, pressing the start button did not respond.


Diagnostic process

1. The customer first called for assistance when the failure occurred. It was a rainy day. The mechanic confirmed that the vehicle was running out of battery and advised the customer to go to the repair shop for inspection after starting the vehicle, but the customer didn’t go shop.

2. The next day, the customer reported that the vehicle appear message “increased battery discharge” so he returned to the shop for inspection.

3. Connect diagnostic computer with car, got many faults which all is about low voltage. Continue to test and there is a standby current fault, start to measure standby current, but the current is normal.

4. Check battery charge status and vehicle driving characteristics. The battery needs to be charged. Charge the battery first and check that the vehicle is free of any attachments and modifications. The standby current test is performed after the charging is completed. The vehicle can quickly enter the standby state. After monitoring for more than an hour, the standby current is recorded at about 0.05A, and the maximum does not exceed 0.08A.

5. Use IMIB to monitor that the standby current did not appear too high for a day, monitor the standby current after driving a period of time, no abnormalities were found. The time has been almost two days. There was no stand current failure during the entire inspection process, and no battery discharge increased Failure appears, so we recommend the customer to drive away.

6. Half a month after delivery, it coincided with another rainy day, and the customer again reported that the vehicle could not be started.

7. This time we drove the vehicle directly back to the factory for inspection. The fault code is almost the same as the first one, and it is still a standby current fault. So we immediately performed a standby test. IMIB still showed a current of about 11A after half an hour. When the power distribution box on Z3*2b is disconnected, the current returns to normal. The circuit diagram F502 is to power the power distribution box in engine room. Plug in Z3 * 2B again. When the front power distribution box X60183 is unplugged, the current is restored to normal, the plug is used to power the electric coolant pump.


8. Measure (U-EWP <4) voltage 0V at X60003 pin 10. After judging the fault by plugging and unplugging the electric coolant pump several times, the vehicle can sleep normally again.

9. Check that the internal insurance of the power distribution box in engine room is normal, the wiring is normal, and the appearance of the electric coolant pump is normal, the plug connection and the ground wire are normal. According to the measured data, it is determined that the fault lies in the electric coolant pump.

10. The failure of the electric coolant pump prevents the module from standby, resulting in exhaustion of battery.

11. After replacing the coolant pump, the car has not experienced a battery exhaustion fault so far.


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