Overview
This document contains the following information:
General
Quiescent current reference value, residual charging current evaluation
Hardware reset
Quiescent current shutoff (except vehicles with interior protection)
Idle state
General
Deep discharge protection prevents excessive discharging of the on-board electrical system battery when the vehicle is parked (rest phase). This ensures that vehicle mobility is retained over a long period of time or at increased no-load currents. Hardware resets mean that increases in quiescent currents caused by faulty components are minimized. . Ton ensure that an increased quiescent current is detected by the energy management, a quiescent current reference value must be stored.
Quiescent 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.
Function requirement
Circuit 15R ON
Operating principle
Measurement of the no-load current reference value is started using the diagnostic tester. The "Measure quiescent current!" message is shown. The diagnostic tester must then be removed and the vehicle locked so that the no-load current will quickly drop. The minimum quiescent current occurring since locking is detected and stored. After the vehicle is "woken up", the measured quiescent current is stored as the quiescent current reference value. The no-load current reference value can be read out using the diagnostic tester.
If the measured quiescent current is within a defined tolerance range, the message disappears. If the quiescent current is too high, a fault message is displayed and measurement is started again.
The on-board electrical system battery is loaded during production with 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) serves as the measure for a sufficiently charged on-board electrical system battery. This value must be above 80 %. If the charge level drops below 80 %, a fault message is shown. 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.
Hardware reset
If the energy management detects an increased quiescent current, it attempts to reset the reason causing it by disconnecting the on-board electrical system battery from the on-board electrical system. All consumers on circuit 30t are disconnected from the power supply. After a defined period of time, the on-board electrical system battery is connected again to the on-board electrical system. All consumers on circuit 30t are then supplied with voltage again. If the required affect is not achieved a hardware reset is repeated a maximum of two times. If the quiescent current is still too high, the on-board electrical system battery remains connected to the on-board electrical system. The effect of the increased quiescent current is to discharge the on-board electrical system battery.
Quiescent current shutoff (except vehicles with interior protection)
The quiescent current shutoff prevents deep discharge of the on-board electrical system battery. If the charge level of the on-board electrical system battery drops below 40 %, the energy management disconnects the on-board electrical system battery from the on-board electrical system. Before this, the energy management sends a signal over the CAN as advance notice of the shutoff. This signal is relevant for all control units that are supplied with voltage via circuit 30t. All consumers on circuit 30t are disconnected from the power supply. The on-board electrical system battery then remains permanently disconnected from the on-board electrical system.
The following events prevent the on-board electrical system battery being disconnected from the on-board electrical system:
Change in circuit status (circuit 15R ON or circuit 15 ON)
Hazard warning flasher function active
An active anti-theft alarm system (ATA) alarm (vehicles with ATA)
Panic alarm active (vehicles with panic alarm function)
External charging
Increased quiescent currents owing to active applications or functions (e.g. radio, standing light, evaporator drying, run-on times) are permitted, and they do not disconnect the on-board electrical system battery from the on-board electrical system.
The on-board electrical system battery is switched on again when one of the following events occurs:
Unlocking of vehicle through central locking system
Change in circuit status (circuit 15R ON or circuit 15 ON)
Diagnosis requests
Idle state
The quiescent state is activated via the multimedia system. All electrical consumers that are supplied with voltage through circuit 30t are switched off 5 minutes after the ignition is switched off. The multimedia display then shows the remaining service life in weeks and the current charge level of the on-board electrical system battery. If the quiescent state cannot be started, the message "Function not available!" appears (the charge level of the on-board electrical system battery does not permit the function). When in quiescent state, the vehicle can be parked for am extended period without any energy loss. The on-board electrical system battery is preserved. The interior protection (vehicles with interior protection) is then not active. Connections to online services are also not possible. If the displayed remaining service life is exceeded, the on-board electrical system battery may need to be charged. The quiescent state is deactivated by switching on circuit 15.
Function schematics | |||
Quiescent current management, function schematic | Model 118, 177, 247Model 167, 293Model 213, 238, 257, 290 as of model year 2021 | ||
Control units | |||
Basic function of signal acquisition and actuation module | Model 118, 177, 247 | ||
Basic function of signal acquisition and actuation module at front | Model 167, 293 | ||
Components | |||
Battery sensor, basic function | Model all (CAR) | ||
On-board electrical system battery, basic function |