Energy Diagnosis
Energy Diagnosis
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 procedure reads all the necessary data from the corresponding control units (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. The number of information items varies.
This information includes the possible causes of a flat battery or a vehicle electrical system fault. Look at the list of possible fault causes, then select the number of the relevant causes in order to bring up detailed information, instructions and the associated diagnosis codes. If there are several possible fault causes, they are listed in order of the kilometre reading at which they occurred (most recent first).
For example: the vehicle does not 'go to sleep' (sleep inhibitor); the vehicle is wakened time and again; the side lights were switched on for too long, etc.
- Standard information: This information can always be displayed (driving profile, stationary profile and - only if an IBS is fitted - evaluation of the closed-circuit current measurement data, information on the battery, for example battery charge state, of the last 5 days).
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 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.
- Unfavourable customer behaviour:
- 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 immobilisation period.
- Unfavourable driving profile (short-distance driving).
- Frequent use of auxiliary consumers or use of auxiliary consumers for a longer period (increased power consumption at a standstill).
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: 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 maximum number of wakings within an off-load phase (terminal R off) within the last 5 weeks
- The last 5 control units that prevented the vehicle from going to sleep (with kilometre reading of each event)
- 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 immobilised for a longer period without being wakened.
When all 6 data records in the data memory are full, the oldest data record is overwritten.
- As of model year 03/2007 (JBE2), the last CAN messages that woke the K-CAN bus (with kilometre reading of each event)
- Fault code memory in the JBE
If a bistable relay is fitted, the causes of cutoff of terminal 30g-f are stored in the JBE. There are the following fault cases:
- The battery reached the starting capability limit at terminal R off.
- Up to model year 09/2006: 60 minutes after terminal R off, the vehicle has not yet switched into the rest state.
As of model year 03/2007: The vehicle is not yet in the idle state 10 minutes after cutoff of terminal 30g.
- Up to model year 09/2006: The vehicle was wakened unexpectedly at terminal R off more than 30 times.
As of model year 03/2007: The vehicle was awakened unexpectedly more than 20 times after cutoff of terminal 30g.
- 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
- If an IBS is fitted, the state of charge of the battery of the last 5 days
- The kilometre 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 code memory entry in the event of a closed-circuit current fault and total battery discharge.
- Fault code 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 V. On cutoff, a fault entry is stored.
At undervoltage, the FRM stores a fault code 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.