Engine Off Energy Management, Function - GF54.10-P-1050FR
Model 257, 290 up to model year 2021
Function requirements in general
- "Engine running" or "Drive train operational" signal not set (vehicle switched off).
The CDI control unit (N3/9) (diesel engine) or the ME-SFI control unit (N3/10) (gasoline engine) sends the "engine running" or "drive train operational" signal via the drive train CAN (CAN C1), drivetrain control unit (N127), suspension FlexRay (Flex E), electronic ignition lock control unit (N73) and interior CAN (Can B) to the front SAM control unit (N10/6).
Engine OFF energy management, general
Engine OFF energy management ensures the stability of the on-board electrical system and the starting capability of the engine when the vehicle is parked.
This functionality is integrated in the front SAM control unit and serves to extend the service life of the on-board electrical system battery (G1) To this end, active comfort functions or consumers are switched off. Engine OFF energy management encompasses the following subfunctions:
- Consumer reduction (deactivation of comfort functions)
- Deep discharge protection
- Remote charging/jump start
Additional function requirement for consumer reduction (deactivation of comfort functions)
- Circuit 15 ON or circuit 15R ON
The electronic ignition lock control unit sends the status of terminal 15 to the front SAM control unit over the interior CAN.
Consumer reduction (deactivation of comfort functions)
If the on-board electrical system voltage sinks to below 11.8 V, the front SAM control unit activates the consumer reduction function (switching off of comfort functions). It sends the request for power output limitation or shutoff of consumers over the interior CAN to the relevant control units connected to the interior CAN. It sends the same request over the interior CAN, electronic ignition lock control unit, chassis FlexRay, drivetrain control unit and drive train CAN to the CDI control unit or ME-SFI control unit. Furthermore, it sends the request via the interior CAN, electronic ignition lock control unit and user interface CAN (CAN HMI) to the head unit (A26/17).
Model 257, 290 up to model year 2021 with code B01 (48V technology)
As long as the charge level of the 48 V battery does not drop below a defined limit, the energy requirement of the active consumers is initially assured by an energy transfer from the 48 V on-board electrical system to the 12 V on-board electrical system.
Given constant shutoff conditions, one consumer will be shut off every 5 s in addition to the consumer reduction from the engine ON energy management function.
The shutoff sequence is shown in the table below. The list includes those consumers whose power supply is reduced or shut off as part of the engine ON energy management function (up to shutoff stage 20).
| Sequence | Shutoff stage | Consumers with reduced or no power | Responsible control unit |
|---|---|---|---|
| 1 | 1 | PTC heater booster (R22/3), 1st branch, heat boosting (diesel engine) | Climate control control unit (N22/1) |
| 2 | 2 | PTC heater booster (R22/3), 2nd branch, heat boosting (diesel engine) | Climate control control unit (N22/1) |
| 3 | 3 | PTC heater booster (R22/3), 3rd branch, heat boosting (diesel engine) | Climate control control unit (N22/1) |
| 4 | 4 | PTC heater booster (R22/3), 4th branch, heat boosting (diesel engine) | Climate control control unit (N22/1) |
| 5 | 5 | PTC heater booster (R22/3), 5th branch, heat boosting (diesel engine) | Climate control control unit (N22/1) |
| 6 | 6 | PTC heater booster (R22/3), 6th branch, heat boosting (diesel engine) | Climate control control unit (N22/1) |
| 7 | 9 | Spray nozzle hose heater (with CODE 875 (Heated windshield washer system)) | Front SAM control unit (N10/6) |
| 8 | 10 | Mirror heater | Left front door control unit (N69/1) and right front door control unit (N69/2) |
| 9 | 11 | Seat heater stage 3 (with CODE 401 (Seat climate control for driver and front passenger) or CODE 873 (Seat heater for driver and front passenger)) | Rear SAM control unit (N10/8) |
| 10 | 12 | Rear window heater | Rear SAM control unit (N10/8) |
| 11 | 14 | Seat heater stage 2 (with CODE 401 (Seat climate control for driver and front passenger) or CODE 873 (Seat heater for driver and front passenger)) | Rear SAM control unit (N10/8) |
| 12 | 15 | Rear blower P = 50% (with code 581 (Automatic air conditioning)) | Climate control control unit (N22/1) |
| 13 | 16 | Front blower P = 50 % | Climate control control unit (N22/1) |
| 14 | 17 | Fan P = 50 % | CDI control unit (N3/9) (diesel engine) or ME-SFI [ME] control unit (N3/10) (gasoline engine) |
| 15 | 18 | Trunk socket, cigarette lighter (with CODE 301 (Smoker package)) | Front SAM control unit (N10/6) |
| 16 | 20 | Seat heater stage 1 (with code 401 (Seat climate control for driver and front passenger) or code 873 (Seat heater for driver and front passenger)) | Rear SAM control unit (N10/8) |
| 17 | 20 | Seat ventilation (with CODE 401 (Seat climate control for driver and front passenger)) | Rear SAM control unit (N10/8) |
| 18 | 21 | Residual heat utilization (with code 581 (Automatic air conditioning)) | Climate control control unit (N22/1) |
| 19 | 22 | Rear blower P = 0 % (with code 581 (Automatic air conditioning)) | Climate control control unit (N22/1) |
| 20 | 23 | Stationary heater (with CODE 228 (Stationary heater)) | Climate control control unit (N22/1) |
| 21 | 24 | Telematics, audio, telephone, GPS | Head unit (A26/17) |
The power output limitation or the deactivation of consumers is not canceled even if the on-board electrical system voltage stabilizes at a value above 11.8 V. The output limitation or shutoff of consumers is only canceled again after an engine start.
Deep discharge protection
Deep discharge protection prevents excessive discharging of the onboard electrical system battery when the vehicle is at a standstill (rest phase). This ensures that startability of the engine is retained over a long period of time or at increased no-load currents. Furthermore, increased no-load currents resulting from hardware resets caused by defective components are also minimized. The function is integrated in the front SAM control unit (energy management) and in the electronic ignition lock control unit (closing and security).
The deep discharge protection function comprises the following subfunctions:
Additional function requirements for no-load current reference value/residual charging current assessment
- Circuit 15R ON
The electronic ignition lock control unit sends the status of terminal 15 to the front SAM control unit over the interior CAN.
No-load current reference value/residual charging current evaluation
After the vehicle has gone through production testing and possible runs on the test track, the no-load current has to be measured and an assessment made of the residual charge current of the on-board electrical system battery.
Measurement of the no-load current reference value is started via the diagnostic tester. The message "Measure no-load current!" appears in the instrument cluster (A1). The front SAM control unit sends the request to display the message to the instrument cluster via the interior CAN, electronic ignition lock control unit and the user interface CAN. The diagnostic tester must then be removed and the vehicle locked so that the vehicle's no-load current will quickly drop.
The minimum no-load current which has occurred since locking is continuously captured by the battery sensor (B95) (except code U98 (LITHIUM-ION STARTER BATTERY (LISB))) or by the control electronics in the on-board electrical system battery (with CODE U98 (LITHIUM-ION STARTER BATTERY (LISB))) and stored. After the vehicle has "woken up", the battery sensor or the control electronics in the on-board electrical system battery sends the measured no-load current value via the battery sensor LIN (LIN B15) to the front SAM control unit, which then saves this value as the no-load current reference value in the non-volatile memory. The no-load current reference value can be read out using the diagnostic tester.
If the measured no-load current is within a defined tolerance range, the message in the instrument cluster disappears.
If the no-load current reference value is too high, a no-load current fault message appears in the instrument cluster and measurement is started again.
During production, charge is removed from the battery in the course of various function tests. The charge level of the on-board electrical system battery must therefore be assessed at the end of assembly. The charge level (ratio of current charge to the maximum storable charge in the on-board electrical system battery) serves as the measure for a sufficiently charged on-board electrical system battery. This value must be above 80%. If the charge level is below 80 %, a fault message is shown in the instrument cluster. Measurement of the residual charge current is only done following successful measurement of the no-load current reference value. As a rule, the two values are released together.
Additional function requirements for no-load current shutoff
- Circuit 15R OFF
The electronic ignition lock control unit sends the status of terminal 15 to the front SAM control unit over the interior CAN.
No-load current shutoff
The no-load current shutoff prevents deep discharge of the on-board electrical system battery and is started under the following conditions:
- High no-load current
- Charge level of on-board electrical system battery below 40 % (not for vehicles with code B01 (48V technology) and not for vehicles with code 882 (Interior protection and tow-away protection) in locked condition)
The charge level of the on-board electrical system battery and the onboard electrical system load are captured by the battery sensor or by the control electronics in the on-board electrical system battery.
The battery sensor or the control electronics in the on-board electrical system battery communicate with the front SAM control unit via the on board electrical system LIN.
If one of the conditions for activation of no-load current shutoff occurs, the front SAM control unit actuates the battery disconnect switch relay (K57/4) in the engine compartment prefuse box (F32/3) in the OPEN direction after a time of 10 min. Beforehand, the front SAM control unit sends a signal via the interior CAN as advance notice of shutoff. This signal is relevant for all control units that are supplied with voltage via circuit 30t. All consumers that are supplied with voltage via circuit 30t are then switched off.
The following events prevent opening of the battery disconnect switch relay:
- Change in circuit status (circuit 15R ON or circuit 15 ON)
- Hazard warning flasher function active
- Anti-theft alarm system (ATA) alarm (with code 551 (Anti-theft alarm system (ATA)))
- Panic alarm active (with code 763 (Radio remote control with panic switch))
- External charging
If the battery disconnect switch relay was opened due to the charge level of the on-board electrical system battery, it remains open permanently.
If the battery disconnect switch relay was opened due to excessive no-load current, the electronic ignition lock control unit control unit actuates the battery disconnect switch relay in the close direction after a defined period of time has expired. All consumers on circuit 30t are then supplied with voltage again.
The brief opening of the battery disconnect switch relay may cause resetting of the no-load current consumers (hardware reset). If the no-load current is still too high, the battery disconnect switch relay is opened and closed again a maximum of two more times. If the no-load current is still too high, the battery disconnect switch relay remains closed permanently.
Increased no-load currents owing to an active application or function (e.g. radio, standing lights, stationary heater (with code 228 (Stationary heater)), evaporator drying) are permitted and do not cause the battery disconnect switch relay to open.
The battery disconnect switch relay is closed again if one of the following events occurs:
- Unlocking of the central locking
- Change in circuit status (circuit 15R ON or circuit 15 ON)
- Diagnostic command from the electronic ignition lock control unit
The no-load current shutoff can also be triggered manually through a corresponding menu in the head unit (Rest mode) (except code B01 (48V technology)). In this case, all electrical consumers that are supplied with voltage via circuit 30t are switched off 15 min after the ignition is switched off. The remaining service life in weeks is then shown in the Audio/COMAND display (A40/8). If the rest mode cannot be started due to an active fault, the message "Function not available!" appears. If the rest mode cannot be started due to the charge level of the battery, the message "Charge level too low for rest mode" appears. The head unit sends the "Activate rest mode" request via the user interface CAN, electronic ignition lock control unit and interior CAN to the front SAM control unit, which then starts the no-load current shutoff. The front SAM control unit then sends information for displaying the remaining service life or for outputting the message via the interior CAN, electronic ignition lock control unit and user interface CAN to the head unit. The head unit then actuates the display in the Audio/COMAND display via the high-speed video link signal line.
Remote charging/jump start
If the on-board electrical system battery does not have enough capacity to start the engine, the on-board electrical system battery must be charged or a jump start carried out.
Model 257, 290 up to model year 2021 with code B01 (48V technology)
If the battery output of the 48 V battery is very low when the engine is started (P < 5.2 kW), the starting capability can be established by transferring energy from the 12 V on-board electrical system to the 48 V on-board electrical system.
If an external charger is connected and the DC/DC converter control unit measures a voltage higher than 12.8 V in the 12 V on-board electrical system, then energy is transferred at a maximum output of 500 W via the DC/DC converter control unit to the 48 V on-board electrical system and the 48 V battery is charged.
| Electrical function schematic for comfort function shutoff | PE54.10-P-2076-97XBA | ||
| Electrical function schematic for no-load current management | PE54.10-P-2074-97XBA | ||
| Overview of energy management system components | GF54.10-P-9990FR |