Engine Off Energy Management, Function - GF54.10-P-1050RFM
Model 205
as of model year 2019
Model 253 (except 253.99)
as of model year 2020
Model 253.99
The "Engine off" operating status on vehicles with a combustion engine is equivalent to the "No energy transfer from high-voltage on-board electrical system to 12 V on-board electrical system" status on model 253.99.
Function requirements, general
- "Engine running" or "Drivetrain operational" signal not set (vehicle switched off) (except model 253.99)
- No energy transfer from high-voltage on-board electrical system to 12 V on-board electrical system (model 253.99)
Model 205
as of model year 2019
Model 253 (except 253.99)
as of model year 2020
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).
Model 253.99
The drivetrain control unit sends information on the operating mode of the DC/DC converter control unit (N83/1) over the suspension FlexRay, electronic ignition lock control unit and the interior CAN to the front SAM control unit.
Engine OFF energy management, general
The engine OFF energy management ensures the stability of the on-board electrical system and the starting capability of the engine when the vehicle has been switched off (except model 253.99) or it ensures the stability of the on-board electrical system when there is no energy transfer from the high-voltage on-board electrical system to the 12 V on-board electrical system over the DC/DC converter control unit (model 253.99).
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 (except model 253.99)
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.
The automatic circuit switch back function causes circuit 15 to be switched back after 15 minutes without any customer action to circuit 15R and circuit 15R to be switched back after another 30 minutes to circuit 15C. The consumer reduction is terminated with the transition to circuit 15C.
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 205
as of model year 2019
with code B01 (48V technology)
Model 253 (except 253.99)
as of model year 2020
with code B01 (48V technology)
If the "Drivetrain operational" signal is set, the energy requirement of the active consumers is initially provided by the transfer of energy from the 48 V on-board electrical system to the 12 V on-board electrical system, until the charge level of the 48 V battery (G1/3) drops below a defined limit value.
Model 205.012/013/047/053/147/212/213/247/253
as of model year 2019
Model 253.311/353/354/911/953/954
as of model year 2020
Model 253.99
If the "Drivetrain operational" signal is set, the energy requirement of the active consumers is initially provided by the transfer of energy from the high-voltage on-board electrical system to the 12 V on-board electrical system, until the charge level of the high-voltage battery (A100g1) drops below a defined limit value.
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 | Blower in front 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) or CODE 965 (Taxi/rental car preinstallation)) | 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 any impermissibly high discharging of the on-board electrical system battery when the vehicle is at a standstill (stationary phase) by opening the battery disconnect switch relay (K57/4). The battery disconnect switch relay switches circuit 30t. On vehicles with a combustion engine, the deep discharge protection ensures the starting capability of the engine over an extended period of time or with an increased quiescent current. 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:
- Quiescent current reference value/residual charging current evaluation (production mode)
- Quiescent current shutoff by reset
- Quiescent mode
Additional function requirements for quiescent current reference value/residual charging current evaluation (production mode)
- 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.
Quiescent current reference value/residual charging current evaluation (production mode)
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 occurring since locking, is recorded and stored by the battery sensor (B95). After the vehicle is "woken up", the battery sensor sends the measured no-load current value over the battery sensor LIN (LIN B15) to the front SAM control unit, which then saves it as the no-load current reference value in the nonvolatile 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 quiescent current shutoff by reset
- 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.
Quiescent current shutoff by reset
Quiescent current shutoff prevents any deep discharge of the on-board electrical system battery and it is started when an impermissibly high quiescent current is detected.
The quiescent current is recorded by the battery sensor.
The battery sensor communicates over the battery sensor LIN with the front SAM control unit.
The front SAM control unit evaluates the signal and, if the quiescent current is impermissibly high, it opens the battery disconnect switch relay in the engine compartment prefuse box (F32/3) after a defined period of time. 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 electronic ignition lock control unit closes the battery disconnect switch relay after a defined period of time is expired. All consumers on circuit 30t are then supplied with voltage again.
This brief opening of the battery disconnect switch relay also resets the no-load current consumers if necessary (hardware reset). If the no-load current is still too high after the first reset, 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, even after the third reset, 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 electronic ignition lock control unit monitors the activity on all the CAN buses. If a CAN bus is active for an impermissibly long period of time, the electronic ignition lock control unit sends a "Bus keep awake control unit" request over the interior CAN to the front SAM control unit, which then starts the quiescent current shutoff through a reset.
Additional function requirements for quiescent mode
- 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.
Quiescent mode
The quiescent mode prevents any deep discharge of the on-board electrical system battery and it is started when the charge level of the on-board electrical system battery drops below 40 % (not on 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 on-board electrical system load are detected by the battery sensor.
The battery sensor communicates over the battery sensor LIN with the front SAM control unit.
The front SAM control unit evaluates the signal and at a critical charge level of the on-board electrical system battery, it opens the battery disconnect switch relay in engine compartment prefuse box after a defined period of time. 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 551 (Anti-theft alarm system (ATA)) and code 460 (Canada version) or code 494 (USA version))
- External charging
- Remote start active
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
- Driver door opened
The quiescent mode can also be manually activated through a corresponding menu in the head unit. In this case, all electrical consumers supplied with voltage through circuit 30t, are switched off after a defined period of time after the ignition has been 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 quiescent mode" request over the user interface CAN, electronic ignition lock control unit and the interior CAN to the front SAM control unit, which then actuates the shutoff procedure. 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 (except model 253.99)
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 205
as of model year 2019
with code B01 (48V technology)
Model 253 (except 253.99)
as of model year 2020
with code B01 (48V technology)
If the battery output of the 48 V battery is very low (P < 5.2 kW) when the engine is started, the starting capability can be assured by the transfer of 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 over the DC/DC converter control unit into the 48 V on-board electrical system and the 48 V battery is charged.
Model 205.012/013/047/053/147/212/213/247/253
as of model year 2019
Model 253.311/353/354/911/953/954
as of model year 2020
If the battery output of the high-voltage battery is very low (P < 8 kW) when starting the hybrid drive system, the starting capability can be established through an energy transfer from the 12 V on-board electrical system to the high-voltage on-board electrical system.
If, when the engine hood is open, an external charger is connected and the power electronics control unit (N129/1) measures a voltage of more than 12.8 V in the 12 V on-board electrical system, energy with a maximum power of 500 W is transferred via the on-board electrical system battery and the power electronics control unit to the high-voltage on-board electrical system and the high-voltage battery is charged (only with circuit 15 ON).
| Electrical function schematic for no-load current management | PE54.10-P-2074-97FBB | ||
| Electrical function schematic for comfort function shutoff | PE54.10-P-2076-97FBA | ||
| Overview of energy management system components | GF54.10-P-9990RF |