E90/91/92 Energy Diagnosis Hints
Description of the energy diagnosisRunning the energy diagnosis
A breakdown due to a depleted battery or problems in the vehicle energy system can have a wide variety 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 test module helps find the cause of the problem.
Result of the energy diagnosis
The test module reads all the necessary data from the corresponding control modules (see below). After evaluating this data, it displays the following information:
- Conspicuous information: this information is only displayed if there was a problem in the vehicle energy system. For example: the vehicle does not 'go to sleep' (sleep inhibitor); the vehicle is wakened time and again; the position light was switched on for too long, etc.
- Standard information: This information can always be displayed (battery, driving profile, stationary profile, and- only if an IBS is fitted- evaluation of closed-circuit current measurement data)
On the basis of this information, it can then be decided what the real cause of the fault is.
Overview of possible causes
A breakdown due to a depleted battery or a problem in the vehicle energy system is not necessarily the result of a defective battery. However, in some cases the battery can be damaged- no matter what the cause. The various causes can be placed in two main categories:
- Vehicle faults:
- The vehicle does not "go to sleep".
- The vehicle keeps being woken up.
- Excessive closed-circuit current.
- Defective generator.
- Defective battery.
- Unfavorable customer behavior:
- Position light, parking light or hazard warning lights were switched on for too long.
- Terminal R or terminal 15 was switched on for too long.
- Long immobilization period.
- Unfavourable driving profile.
Data from the vehicle that is read and evaluated
For energy diagnosis, the evaluated data in the vehicle is not changed.The energy diagnosis can be run a number of times and normally always provides the same result.
The energy diagnosis normally provides the same result after repairs, as the data is still present in the vehicle. Even after deleting the fault memory, the data from the energy history memory is still stored. However, at the latest when the energy history memory is overwritten with new data, the repaired fault cause is no longer displayed as result of the energy diagnosis.
This information in detail:
- Energy history memory in the JBE (Junction Box Electronics)
The energy history memory (NB: not to be confused with the history memory for fault code memory entries) stores a variety information that can help in searching for the cause of problems in the vehicle energy system. The stored information of the energy history memory in detail:
- The maximum number of wakings within an off-load phase (terminal R off within the last 5 weeks
- The last 5 control modules that prevented the vehicle from going to sleep (with kilometer reading of each event)
- The driving profile of the last 5 weeks
- Fault memory in the JBE
If a bistable relay is fitted, the causes of cutoff of terminal 30 g-f are stored in the JBE. There are the following fault cases:
- The battery reached the starting capability limit at terminal R off.
- 60 minutes after terminal R off, the vehicle has not yet switched into the idle state.
- The vehicle was wakened unexpectedly at terminal R off more than 30 times.
- Diagnosis requests of the DME/DDE
The DME/DDE stores various data that is used for the energy diagnosis:
- If an IBS is fitted, the last 32 cycles of the closed-circuit current monitoring are stored
- The last registered battery replacement
- The state of charge of the battery in the last 5 days
- The kilometer readings of the last 5 days
- If an IBS is fitted, the auxiliary consumer units that were switched on during the last 32 cycles, for example, light or independent heating.
- Fault memory in the DME/DDE
If an IBS is fitted, the DME/DDE stores a fault memory entry in the event of a closed-circuit current fault and total battery discharge.
- Fault memory of the FRM (footwell module)
The FRM is responsible for control of the lights. At terminal R off, the FRM switches the lights off if the voltage falls below approx. 11 Volts. On cutoff, a fault memory entry is stored. At undervoltage, the FRM stores a fault memory entry. The environment related conditions can be used to determine whether terminal R, terminal 15 or a statutory consumer unit (e.g. light or hazard warning lights) was switched on.
Possible causes - unfavorable customer behavior
Unfavorable customer behavior with vehicle faults is a main cause of breakdowns due to a depleted battery. In detail, the following individual causes can be determined:
Position light, parking light or hazard warning lights were switched on
The position light, parking light or hazard warning lights were switched on for too long with the vehicle parked. If possible, point out these facts to the customer.
Terminal R or terminal 15 was switched on
Terminal R or terminal 15 were switched on for too long while the engine was off. The current consumption of the vehicle is then, depending on the equipment, 10-15 A. This discharges the battery very quickly. If possible, point out these facts to the customer.
Long immobilization period
The vehicle was parked for a very long period. The vehicle has a standard closed-circuit current consumption of 10-40 mA, depending on the equipment fitted. This leads to slow but continuous battery discharge. Depending on the state of charge of the battery when the vehicle is parked, the residual capacity necessary to start the vehicle is reached after an immobilization period of approx. 4-12 weeks. If possible, point out these facts to the customer.
Unfavorable driving profile
The battery can be depleted due to unfavorable driving characteristics of the customer:-
- In the case of extreme short-distance driving, it is possible that starting the engine takes more energy from the battery than is charged in the subsequent trip. The charge balance deteriorates if a great many current consumers are switched on during the subsequent trip.
- Very few trips: If the vehicle is moved very infrequently and the individual trips are not sufficiently long, it is possible that during the immobilization period more energy is taken from the battery by normal closed-circuit current than is charged while the vehicle is being driven. If possible, point out these facts to the customer.
Terminal control
The terminal control is distributed across various control modules. The following block diagram provides an overview of the control modules involved and the integration in the vehicle electrical system.
There are the following terminals:
Terminal 30:
Terminal 30 is routed from the battery terminal via the safety battery terminal to the front distribution box. As soon as the battery is connected to the terminals, terminal 30 is live. Terminal 30 is at approx. 40 fuses of the distribution box.
Control modules supplied by terminal 30:
Terminal 30 g:
Terminal 30 g is controlled by the CAS. When the overall vehicle is wakened by an operation of the user, terminal 30 g is switched on. Terminal 30 g is automatically switched off after a codable after-run time (e.g. 30 minutes). The after-run time starts with the event terminal R Off. As in the case of terminal 15, a relay in the distribution box is activated by the CAS via a semiconductor switch. The relay of terminal 30 g switches the battery voltage to approx. 18 fuses in the distribution box.
Control modules supplied by terminal 30 g:
Terminal 30 g-f:
Terminal 30 g-f is a terminal 30 that is only switched off of faults are detected.
Terminal 30 g-f only exists if a bistable relay is fitted. The relay is not visibly arranged in the distribution box. As a rule, the bistable relay is only fitted together with the IBS. On vehicles with CCC, M-ASK or independent heating, a relay of this kind is fitted. On some equipment variants with TCU, a bistable relay is also fitted. On vehicles without terminal 30 g-f, the corresponding fuses (approx. 2) are supplied with terminal 30 g.
The JBE activates the relay of terminal 30 g-f. The JBE can switch terminal 30 g-f on or off via a bistable relay in the distribution box. As a rule, the bistable relay is always switched on. The bistable relay has two relay coils and it always remains in the last state activated (switched on or switched off).
The following three faults exist in which terminal 30 g-f is switched off:
1. As of approx. 60 minutes terminal R off, the DME/DDE starts a closed-circuit current measurement using the IBS. When the DME/DDE determines a closed-circuit current fault, this wakes up the vehicle and sends a message for cutoff of terminal 30 g-f. The JBE receives the message and switches the bistable relay off. Increased closed-circuit current due a switched-on auxiliary consumer unit is not a closed-circuit current fault for the DME/DDE. Nonetheless, terminal 30 g-f is switched off even if the starting capability limit is reached. The command for cutoff of terminal 30 g-f is also issued in this case by the DME/DDE.
2. As of terminal R off, the JBE monitors whether the vehicle is able to go into the idle state. The vehicle can only enter the idle state when all the control modules are ready for this. If not all control modules have signaled this readiness approx. 30 minutes, the JBE switches terminal 30 g-f off. The JBE also stores all the control modules in the energy history memory that have not signaled readiness for the idle state.
3. A few minutes after terminal R off, the vehicle has normally switched into the idle state. As of the idle state, the JBE counts how often the vehicle is wakened. The JBE switches terminal 30 g-f off when a vehicle has been wakened unexpectedly more than 30 time with terminal R off. The JBE also stores the maximum number of waking events in the energy history memory.
In all cases of cutoff, a fault is entered in the JBE. The cutoff of terminal 30 g-f is independent of what triggered the detected fault. The cutoff is only an attempt to remedy the fault in the vehicle and prevent it from not starting. The cutoff of terminal 30 g-f does not necessarily mean that there was a fault in a consumer unit of terminal 30 g-f.
The switch-on condition for terminal 30 g-f is the switch-on of terminal R. This is why terminal 30 g-f is always switched on with terminal R or terminal 15.
Control modules supplied by terminal 30 g-f.
Terminal 15:
Control of terminal 15 is by the CAS depending on operation of the start/stop button (with the key inserted in the key slot). Terminal 15 is switched in the CAS via semiconductor switch. A relay in the distribution box is activated via the output of a semiconductor switch. The relay switches the voltage of the battery to approx. 7 fuses in the distribution box. The consumer units of terminal 15 are essentially supplied from here.
Control module supplied by terminal 15:
PDC Park distance control
For safety reasons, some control modules have a terminal 15 line directly from CAS, e.g. the FRM (footwell module).
Terminal 87:
The DME/DDE controls terminal 87 via a relay in the E-box. Terminal 87 is switched on as of terminal 15. After terminal 15 has been switched off, terminal 87 is switched off by the DME/DDE with a slight delay. No control modules are supplied by terminal 87.
Terminal R:
Terminal R is not present as a hardware terminal. The status of terminal R is only communicated from CAS via the bus systems.
Possible causes - vehicle faults
Unfavorable customer behavior with vehicle faults is a possible cause of breakdowns due to a depleted battery. In detail, the following individual causes can be determined:
Vehicle does not "go to sleep"
If the vehicle does not reach the idle state after terminal R Off, i.e. the bus systems remain active, the causing control module is normally determined by the energy diagnosis. The troubleshooting must be continued in the peripherals (e.g. defective sensor or switch) of each control module. If no fault is determined, replace the control module.
If a number of control modules on the PT-CAN bus are entered as cause in the energy history memory at the same kilometre reading, the wake-up line should be checked:
- Short circuit to ground or positive
- Loose contact
- First, check the connections of the wake-up line on the IBS (if fitted), CAS and JBE
On vehicles with fitted IBS: If terminal 15 can no longer be switched using the START-STOP button or the electrical steering interlock (ELV) cannot be unlocked, check the installation location of the battery for traces of dampness and examine the fault code memory entries regarding the IBS: IBS can be defective due to moisture and keep the wake-up line at high level. In this case, replace the IBS.
NB! Operation by the customer can also lead to an entry in some control modules: e.g. listening to the radio with terminal R OFF leads to the registration of RAD, RAD2 or M-ASK and possibly CID with the same kilometre reading as cause in the energy history memory.
Vehicle keeps being woken up
If the vehicle is wakened time and again, the maximum number of wakings in an off-load phase (terminal R OFF) for the last 5 weeks is determined. The causing control module cannot be determined automatically: Identify the possible cause by disconnecting fuses or disconnecting the corresponding control modules step by step.
If it was possible to determine the waking control module, troubleshooting must then be continued in the peripherals (e.g. defective sensor or switch, loose contact) of the control module. If no fault is determined, the control module must be replaced.
Note: In exceptional cases, it is possible that the result "Vehicle keeps being woken up" is generated by unfavourable customer behaviour, e.g. frequently waking the vehicle at terminal R OFF by opening and closing the luggage compartment lid or doors.
Excessive standby current
The result "Excessive closed-circuit current" means that the vehicle, occasionally at least, has had a closed-circuit current greater than 80 mA. Here, the vehicle was in the idle state, that is, the bus systems were inactive.
A possible cause of this could be defective control modules. As troubleshooting, run a closed-circuit current measurement and identify possible causes by disconnecting fuses or disconnecting the corresponding control modules step by step.
Procedure for external closed-circuit current measurement: see Service Information number 61039947.
Battery or generator defective
Even though the battery was not the cause of the complaint, it might have been damaged beforehand due to deep discharge for a longer period. For this reason, check the battery condition if you suspect that the battery might have been damaged beforehand.
See "Master document, battery" BMW Service Technology:
TIS -> Document -> SI Technology -> Enter
SI number SI number: 610702875
If there is a suspicion that the generator is defective, it must be determined whether the DME/DDE has relevant fault memory entries. Fault memory entries with regard to the IBS must also be taken into account.
If the vehicle comes to a standstill and will not start during or shortly after a journey, the cause probably lies in the charge balance of the generator. A requirement here is that the charged battery was still able to deliver adequate current for the starting operation.
Cutoff closed-circuit current fault
General functional description of power supply, see BMW Technology: TIS -> Document -> SI Technology -> Enter SBT number SBT number: -> 61 03 04092
In the 5 Series and 6 Series as of E60, there is the micro-power module (MPM). In the event of a fault, the MPM disconnects some control modules from the on-board supply voltage by means of a bistable relay. Primarily, MOST control modules are supplied from this terminal.
In the 1 Series and 3 Series as of E87, there is also a bistable relay (depending on variant). In the event of a closed-circuit current fault, the bistable relay cuts off certain consumer units from the on-board supply voltage.
The switched terminal of the bistable relay is called terminal 30 g-f. Terminal 30 g-f stands for a terminal 30 that is switched (g) in the event of a fault (f).
Bistable relay (depending on variant)
For cutoff in the event of a closed-circuit current fault, there is a bistable relay. The bistable relay is arranged on the board of the distribution box (hidden by the body of the distribution box).
The bistable relay switches terminal 30 through to the fuses F17 and F40. In the event of a closed-circuit current fault, this relay is activated to interrupt the power supply of the fuses mentioned. The bistable relay has two relay coils that open or close the relay contact as the case may be when activated. The relay stops and stays in the last activated position (contact open or closed).
Variant without bistable relay
The bistable relay is only present with certain optional extras. In vehicles without a bistable relay, the fuses F17 and F40 are connected by a bridge to terminal 30 g.
Activation of bistable relay
The bistable relay is on the distribution box and is activated by the junction box electronics (JBE). The activation lines run via the internal connector X04010 of the junction box (consisting of distribution box and JBE). The relay coils are supplied on the distribution box directly via terminal 30. The JBE switches the negative lead onto the relevant relay coil for a short time to open or close the contact.
Conditions required for switch-off, terminal 30 g-f (fault)
In the event of a fault, the bistable relay is activated by the JBE in such a way that the power supply of terminal 30 g-f is interrupted. Terminal 30 g-f is switched off if any of the following conditions occurs:
- With terminal R off, the JBE counts more than 30 wake-ups at terminal R.
- After 30 minutes of terminal R off, the JBE detects control modules that are preventing the vehicle from entering the sleep mode.
- With terminal R off, the DME/DDE detects via the IBS that the starting capability limit has been reached (battery capacity is just enough to start the vehicle).
If terminal 30 g-f is switched off due to a closed-circuit current fault, a fault code memory entry is entered in the JBE.
When terminal 30 g_f is switched off, it is not taken into account which control module is responsible for the closed-circuit current fault. In all cases, terminal 30 g-f is switched off. If the closed-circuit current fault is caused by a control module that is not supplied by terminal 30 g-f, the closed-circuit current fault remains even after cutoff.
Conditions required for switch-on, terminal 30 g-f
A switch-on condition always has priority over a switch-off condition. Under the following conditions, terminal 30 g-f is switched on again via the bistable relay.
- Vehicle is unlocked
- Terminal change from terminal R off to terminal R or terminal 15
- Change in a status of door, engine hood or trunk lid The switching on is only run if the relay was previously switched off.
After every power interruption of the JBE, the bistable relay is activated in such a way that the contact is closed. In the normal case, terminal 30 g-f is always switched on. With terminal R or terminal 15, terminal 30 g-f is always switched on.