Fix BMW won’t start as fault "high rate of battery discharge"

We want to share a real repair case every day, in this post we will discuss BMW fault “high rate of battery discharge” make car won’t start, check below to see how to fix.

Vehicle information

Model: BMW 520Li

Year: 2017

Engine: N20

Chassis: F18


Fault symptom

Car was at garage for one night, next morning to start the car, the engine clicked twice and the dashboard went black for 2 seconds, a waning message came up to idrive screen: high rate of battery discharge, the car did not start.


Fix process

1. Connect ISTA diagnose device with OBD port, got low voltage fault and multiple sleep current fault.

2. Diagnose battery, got information “Vehicle sleep current is greater than 1A, 9 times”. It can be determined that the battery power is exhausted due to the excessive sleep current. We charge the battery fully, then measure that the battery capacity is normal.

3. Measure the sleep current with a current clamp, it was 14.92 amps, which is much larger than normal. What is it that consumes so much power?


4. This car is equipped with a driving recorder, backup camera, GPS, but these devices do not consume so much power.

5. Check other components which need large current:

starter 100A
electric fan10A
oil pump  5A
blower 5A
electric water pump15A

6. Next, found that the electronic water pump was running at high speed after the vehicle was sleeping.


7. After unplugging the water pump, the sleep current drops to 14Ma, a normal current.

8. Why does the pump work all time for no reason? Continue to check pump, found the plug pins are corroded, disassemble the pump and found internal corrosion. Damage to the motor and electronic components caused by the leakage of antifreeze from pump, further causing the pump to work continuously.



9. Replace the pump, start the car ok, no warning light appears.


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