BMW has been using a smart charging system since the launch of the E65/66 7 series. The system works well and assists significantly with the diagnosis of the electrical system. In this post I will go through how the system works, components and what diagnoses can be done with the system.
Components of the System:
- IBS (intelligent battery sensor)
The IBS sensor is small and built into the negative terminal on newer models. The E65/66 had a module called the, “power module” (PM) that monitored voltage use. The IBS will take measurements of battery voltage called, SOC (state of charge). This will also take a measurement called SOH (state of health of the battery).
2. DME (digital motor electronics)
The DME is the computer that controls the engine. The DME is the master for controlling the charging system.
3. Alternator
The component that generates electrical energy to power the vehicle and charge the battery. Some hybrid BMWs will not use an alternator since they use a start motor generator in place. I’ll get into that another time.
4. BSD (bit serial data line)
This is a communication line used for all these components to talk to each other. This is a single wire bus system, that without communication has 12v on the line and when communicating will have a digital square wave pattern.
It all comes together…
The IBS takes a reading of the battery voltage and SOH (state of health). Then, forward these reading over a BSD (bit serial data line) to the DME. The DME makes decisions on how to charge the battery from the reading of the IBS. Then, the DME sends out a command over the BSD to the alternator, for how much to charge the battery. The reason for this system is to save fuel economy. When an alternator is charging, it can put a huge drag on the engine. When charging the battery, it helps conserve fuel. In addition, the alternator is full-fielded during braking to provide a engine brake.
Another part of the smart charging system is energy diagnosis. This system monitors the vehicles battery when asleep and looks for draws on the battery. If the DME determines there is a draw from the IBS data, it will command a relay called 30F to switch off. This will turn power off to a majority of the consumers on the vehicle. The DME will use IBS readings to monitor the draw after the relay switch off. If the DME sees the draw is gone, the DME will keep the relay off until next key start up. Once the vehicle starts up, a warning will come up for high battery drain on the vehicle.
Using BMW software, you can run a test plan called, “energy diagnosis”. This will tell you the cause of high battery drain, charge history of the battery, parking time, history of trips and draw history. To start a test plan could tell you if the vehicle was woken up frequently. Meaning, the vehicle sleep mode was disturbed. That could be for multiple reasons; from a bad comfort access door handle, to a bad module waking the control module communication network. Energy diagnosis could also say the vehicle has a high parasitic draw and even tell you how long and how many amps the draw was. Energy diagnosis can also tell you if the vehicle was short tripped. Short tripping is when you drive the car less than the amount of time it takes to recharge the battery from initial start up. If this is done multiple times, the battery can be drained down. This can also determine if the battery drained because of the car being parked for a long time period. The software can also tell if the lights were left on. Software can also tell if the vehicle was used for a long period without the engine on. Finally, the vehicle can tell you when the battery is aged or faulty and requires replacement.
Replacing your Battery
The battery replacement does have to be the same AH rating and battery type. The DME charging strategy is based on those two items. If you install a battery of different AH rating and battery type the vehicle will not charge this properly and can shorten the life of the battery. BMW does give you options through the programming software to change the battery AH and type.
Once you replace your battery, you will have to register it to the vehicle. Registering is using another test plan to tell the DME that the battery has been replaced. The reason is, as the battery ages it will require more energy to recharge it. The DME takes this into account and will have the alternator charge the battery more as it ages. If you install a new battery and don’t register it, the DME will overcharge it and shorten the life span.
Thanks for reading and message me with questions!
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