BMW Battery Sensor Issue
BMW vehicles equipped with an intelligent battery sensor (2013 335is for example) may exhibit one or more of the following complaints:
Check control message related to battery discharge
Power reduction (reduced blower speed, heated seat operation, etc.)
The following codes may be stored in the DME:
2E8B (intelligent battery sensor signal)
2E8C (intelligent battery sensor function)
2E8D (intelligent battery sensor signal transmission)
2E8E (intelligent battery sensor communication)
The cause may be either a faulty battery or intelligent battery sensor (IBS), but not both. The power management system and IBS cannot determine if the battery needs to be replaced. This is normal operation for all E-Series vehicles because they do not have the Advanced IBS sensor that the F-Series vehicles have.
An external battery tester (Midtronics EXP-1000) must be used to determine if the battery needs to be replaced. Energy Diagnosis will not prompt for a battery replacement unless the battery is “aged.” When energy diagnosis identifies the battery as aged, it means the amount of energy discharge over the course of battery life has reached its maximum (worn out). In most cases, energy diagnosis states that the battery is OK. This is typically an indication of the current state of charge (SoC), not the state of health (SoH). The SoC is defined as the current amount of energy left in the battery (displayed as a percentage). The SoH is defined as an evaluation of the battery condition over a period of time (displayed as a percentage).
Perform diagnosis using ISTA.
If no power management faults are stored and only IBS faults are stored, complete the test plans. Only replace the IBS sensor when prompted by the test plan. If no IBS faults are stored, proceed to the next step.
Test the battery using a Midtronics EXP-1000 battery tester.
As a result of diagnosis, either the battery or the IBS must be replaced. Further analysis has shown that replaced IBS sensor are not defective if they were replaced without a fault code stored.