Function Sequence For No-Load Current Management

• No-load current management ensures the vehicle's starting capability even after extended idle times by actuating the latching terminal relay 30g to switch off consumers that are supplied with voltage via latching terminal relay 30g.
• When ignition switch is OFF, BCM cyclically measures the voltage and power consumption every 6 minutes.
• When no-load electrical system voltage drops below 11.8 V, BCM actuates the latching terminal relay 30g to switch off consumers.
• BCM accommodates to increase power consumption within a maximum of 75 minutes after ignition switch is turned OFF.
• After 75 minutes, if an excessively high no-load current is determined, BCM actuates the latching terminal relay 30g to switch off consumers.
• After 6 hours, BCM actuates the latching terminal relay 30g to switch off consumers.
• BCM transmits the activation of no-load current management via CAN communication before actuating the latching terminal relay 30g.

The no-load current management system comprises the following sub functions:

• Function sequence for no-load current shutoff
• Function sequence for no-load current diagnosis

Function Sequence for No-load Current Shutoff 

Function sequence for requesting consumer shutoff (no-load current switch)

• When ignition switch OFF, BCM starts the 6-hour timer and continuously monitors no-load current by battery sensor via LIN communication. BCM allow to increase power consumption within 75 minutes. After 75 minutes, BCM actuates the latching terminal relay 30g to open If the no-load current is too high. If no-load electrical system voltage drops below 11.8 V, BCM actuates the latching terminal relay 30g prematurely. After 6 hours, BCM actuates the latching terminal relay 30g to open and switch off consumers.

  5 minutes before BCM actuates the latching terminal relay 30g, BCM transmits the shut off signal via CAN communication to all control units receiving power via the latching terminal relay 30g.

Function sequence for shut off consumers

• 5 minutes after shut off signal is transmitted, if there is no reason to stop the operation, BCM actuates the latching terminal relay 30g to open and transmits the status of the latching terminal relay 30g via CAN communication to electronic ignition switch control unit. Then electronic ignition switch control unit transmits the status of the latching terminal relay 30g via CAN communication to the corresponding control units.

Function sequence for energize consumers

• If BCM receives a wake-up signal, BCM closes the latching terminal relay 30g and transmits a signal via CAN communication that the wake-up conditions for the control units are active again. Electronic ignition switch control unit receives this status and transmits it via CAN communication to the corresponding control units. Closing the latching terminal relay 30g causes power to again be supplied via latching terminal relay 30g.

  The following conditions authorize a closing of the circuit 30g relay:

  • Unlocking or opening of door or inserting the key in the key switch
  • Ignition switch ACC
  • Switching on the hazard warning system, position lamps, or parking lamps
  • Activating anti-theft alarm system
  • Triggering panic alarm

Function Sequence for No-load Current Diagnosis 

No-load current diagnosis records data to help troubleshoot possible fault profiles.

Function sequence for activating no-load current diagnosis

• When ignition switch is OFF, battery sensor starts the no-load current diagnosis if one of the following events occurs:
  • On-board electrical system voltage values fall below limits and there is a change in the kilometer reading since the last current fault roll entry caused by under voltage.
  • No-load current increases after ignition switch is OFF and 75 minutes are passed.
• When the first no-load current diagnosis start is an entry in the no-load current fault roll occurs. Following this, the no-load current is cyclically checked. These values are updated if there are significant changes or if the no-load current diagnosis is canceled.
• The following data are stored in nonvolatile memory in the no-load current fault roll:
  • Maximum no-load current during no-load current fault phase
  • Minimum no-load current during no-load current fault phase
  • Voltage of the battery upon occurrence of no-load current fault phase
  • Voltage of on-board electrical system battery at end of no-load current fault phase
  • Duration of no-load current fault phase
  • Kilometer reading
  • Consumer status

Function sequence for terminating/ending no-load current

• The no-load current diagnosis ends when ignition switch is ACC.
• The no-load current diagnosis is canceled when the limit value (11.8 V) for the on-board electrical system voltage is undershot. Battery sensor stops no-load current monitoring for minimizing electricity consumption and then the update of current fault roll is stopped.