Battery Monitoring System

WARNING: This page is about a different car, the 2020 Jaguar XE and 2019 Jaguar XE. However, it is still accessible from the selected car via links, so may be relevant.

When the ignition is switched off, the Battery Monitoring System (BMS) control module records the startup battery state of charge and begins to monitor the startup battery condition.

If the startup battery state of charge falls by 7% from the critical start point, the BMS control module will start to monitor the startup battery for 5 minutes. It also sends a 'Warning' message on the Local Interconnect Network (LIN) bus to the Body Control Module/Gateway Module (BCM/GWM). If the startup battery charge has continued to fall below 50% due to the high quiescent drain current after the 5 minute monitoring period, the BMS control module will determine that the control modules are still 'awake'. The BMS control module sends a 'Shutdown' message on the LIN bus to the BCM/GWM. The BCM/GWM then transmits a 'Shutdown' message on High Speed (HS) Controller Area Netowork (CAN) buses to all control modules, requesting them to shutdown.

The BMS control module will monitor the startup battery state of charge for a further 15 minutes. It determines if the startup battery state of charge is still dropping due to the quiescent drain current. The BMS control module sends a 'Power Disconnect' signal to the BCM/GWM on the LIN bus. Then the BCM/GWM sends a signal to the Quiescent Current Control Module (QCCM) via the LIN bus to open its internal relays. When the QCCM relays are open, the power supply from the startup battery to non-critical control modules is removed. The non-critical control modules are any modules associated with the infotainment system and also the climate control system.

The use of the LIN bus communication makes sure that no other control modules are 'woken' during this process. If CAN bus communication was used, all modules on the CAN bus would be woken by the message.