The BMW Intelligent Battery Sensor (IBS) is a mechanical/electronic device which is connected directly to the negative battery terminal.
The IBS contains a micro-processor that is used to monitor/measure various battery conditions such as:
- Terminal voltage via measurement from B+ to Gnd
- Charge/discharge current via integrated shunt resistor
- Temperature of battery acid via integrated temp sensor
The IBS is able to withstand thermal loads up to 105°C, the chemical effects of the battery acid.
IBS Measuring/Evaluation Function
The measuring/evaluation function of the IBS electronics, continuously measures the following values under all vehicle operating conditions:
- Voltage (6V to 16.5V)
- Current (200A to +200A)
- Closed Circuit Current (0A to 10A)
- Starting Current (0A to 1000A)
- Temperature (-40C to 105C)
When the vehicle is stationary, the IBS is programmed to wake up every 14 sec. and makes the required measurements within approx. 50 ms in order to save power. The measured values from the IBS are provided to the DME by way of the Binary Serial Data Interface (BSD) to calculate the State of Charge and State of Health for the battery.
- State of Charge (SoC) is a calculated condition showing the current charge of the battery. SoC is used during key ”OFF” periods to insure the battery maintains a sufficient charge to start the engine at least one more time.
- State of Health (SoH) tracks the history of the battery. Charge/dis-charge cycles and times are monitored. SoH helps the DME determine the proper charging rates and anticipated battery life. Internal resistance of the battery is calculated by the IBS from the current and voltage dip during engine start. The values are forwarded to the DME to calculate the SoH of the battery.
Software contained in the microprocessor of the IBS utilizes the measured values to calculate the State of Charge (SoC) of the battery during vehicle sleep mode and compares this information with that received from the DME/ECM pertaining to the battery SoC/SoH, during the period of time between engine “OFF” and deactivation of the DME main relay.
The current SoC/battery data is stored in the IBS every 2 hours over a 6 hour time frame, providing 3-2 hour snapshots of battery SoC information. The stored information/snap-shot data is overwritten every 6 hours. Whenever KL15 is activated the IBS updates the DME with the current closed circuit histogram/battery status information, by way of the BSD. Upon obtaining updated information the DME evaluates the new data and if a closed-circuit current draw is identified a fault will be stored in the fault memory of the DME.
Servicing the IBS
The IBS is very sensitive to mechanical stress and strain. It is serviced as a complete unit with the ground cable. The ground cable also serves as a heat dissipater for the IBS.
Particular attention should be paid to the following points in service:
- Do not make any addition connections at the negative terminal of the battery
- Do not modify the ground cable
- Do not make any connections between the IBS and the sensor screw
- Do not use force when disconnecting the ground terminal from the battery
- Do not pull at the ground cable
- Do not use the IBS as a pivot point to lever off the ground terminal
- Do not use the connections of the IBS as a lever
- Use only a torque wrench as described in the repair manual
- Do not release or tighten the sensor screw
A fault code is stored in the DME when the IBS is defective. The DME adopts a substitute value and assumes IBS emergency mode. IBS emergency mode boosts the idle speed in order to sufficiently charge the battery. Direct diagnosis of the IBS is not possible, it can only be diagnosed through the DME. The self-diagnosis function checks the voltage, current, temperature, terminal 15 wake up signal as well as system errors in the IBS.
The software in the DME and that of the IBS must match. To ensure this requirement it may be necessary to replace the IBS in connection with a software update.