Power and Ground Distribution: Testing and Inspection
Energy Diagnosis
Energy diagnosis procedure
The electrical system of BMW vehicles has been subject to an ongoing development process over the last few years. This has led to increased demands being placed on the battery. A breakdown due to a drained battery or problems in the vehicle energy system can have a wide range of causes which, in most cases, are not caused by the battery itself. For this reason, replacing the battery will only rarely provide a sustained solution to the problem. The energy diagnosis procedure helps find the cause of the problem.
Result of the energy diagnosis
The aim of the energy diagnosis is to identify the fault cause as precisely as possible. The procedure reads all the necessary data from the corresponding control units (see below). After evaluating this data, it displays the following information:
- Possible fault causes for a drained battery or problem with the vehicle energy system:
The number of information items varies.
If there are several possible fault causes, they are listed in order of the kilometer reading at which they occurred (most recent first).
For example: vehicle system does not go into sleep mode (sleep mode inhibited); vehicle system is repeatedly woken up; side lights were switched on for too long, etc.
- General information:
this information can always be displayed (results of the last closed-circuit current monitoring, information about battery such as battery states of charge over last 5 days, driving profile, stationary profile).
Based on the information displayed, a decision can be made as to what the actual cause of the fault is.
Overview of possible causes
A breakdown due to a drained battery or a problem in the vehicle energy system is not necessarily the result of a faulty battery. The various causes for discharge of the battery can be placed in two main categories:
- Vehicle faults:
- Vehicle does not assume sleep mode.
- The vehicle keeps being woken up.
- Standby current too high in rest state.
- Faulty alternator (poor charge balance)
- Faulty battery.
- Unfavorable effect of customer benefits:
- Side lights, parking light or hazard warning flashers were switched on for too long.
- Terminal R or Terminal 15 switched on for too long
- Long immobilization period.
- Unfavorable driving profile (short-distance driving).
- Frequent or extended use of auxiliary consumers when engine is not running (e.g. radio or rear seat entertainment system), which can also result in inhibited sleep mode and higher power consumption.
Data from the vehicle that is read and evaluated
This data in detail:
- Fault memory on Central Gateway Module (ZGM)
The ZGM monitors the vehicle condition, registers if sleep mode is prevented or if the system is woken up when it shouldn't be and sends a message to the JBE requesting a reset or that Terminal 30F is switched off.
- Fault registered in JBE (junction box electronics) fault memory
- Reset or switch off of terminal 30F.
- Reset or Terminal 30F switch-off prevented (preconditions not satisfied)
- Startability limit reached with Terminal 15 or Terminal 30B on.
- Energy history memory on the JBE
The energy history memory (NB: do not confuse with the history memory for fault entries) stores various bits of information that can assist in establishing the cause of problems with the vehicle energy system. The stored information of the energy history memory in detail:
- The driving profile of the last 5 weeks
The driving profile is stored in the energy history memory with 6 data records. Each data record contains the following information: Starting time of record the data record, distance travelled in km during recording, number of journeys in different ranges.
A new data record is started as soon as the time difference between the current time and starting time of recording of the current data record is greater than 7 days. This means the time span of the evaluation is usually approx. 35 days if the vehicle was not immobilized for a longer period without being wakened.
When all 6 data records in the data memory are full, the oldest data record is overwritten.
- The maximum number of wake-ups during a rest phase (Terminal R off) within the last 5 weeks
- Diagnosis requests of the DME/DDE
The DME/DDE stores various data that is used for the energy diagnosis:
- The results of the last 24 closed-circuit current monitoring
- The last registered battery replacement
- The state of charge of the battery for each of the last 5 days
- The kilometer readings from the last 5 days
- Time and duration of the last 4 instances of reducing power consumption of or switching off electrical consumers
- As of F10 with enhanced intelligent battery sensor, measured data for monitoring battery condition: faulty battery cell detection, remaining capacity
- Fault memory and diagnosis requests in CAS (Car Access System)
- Fault entry on automatic switch-off of Terminal 15 or Terminal 30B due to startability limit being reached
- History of last extensions of Terminal 30B after-running period (auxiliary consumers that operate when engine is off)
- History of the last CAS wake-up causes
- Fault memory in the DME/DDE
The DME/DDE stores a fault entry in the event of standby current violation, the battery is totally discharged or auxiliary consumers are switched off or their power reduced.
- Fault memory in FRM (footwell module)
The FRM is responsible for control of the lights. At Terminal R off, the FRM switches the side lights or parking lights off if the measured vehicle voltage falls below 10.6 volts for at least 2 minutes. On cutoff, a fault entry is stored.
Events and measures in the event of inhibited sleep mode or unauthorized wake-up
In the event of inhibited sleep mode or unauthorized wake-up, various measures, such as switching off terminals, take effect in succession in order to prevent from total discharge and to ensure the vehicle's starting capability.
Inhibited sleeping:
Unauthorized wake-up:
