Dual Battery System Vehicles

WARNING: This page is about a different car, the 2015 Jaguar XF, 2014 Jaguar XF, and 2013 Jaguar XF. However, it is still accessible from the selected car via links, so may be relevant.

Two batteries are fitted to accommodate the dual battery system used for the Intelligent Stop/Start system. For additional information, refer to

Starting System - V8 5.0L Petrol/V8 S/C 5.0L Petrol - DESCRIPTION AND OPERATION .

Starting System - V6 S/C 3.0L Petrol - DESCRIPTION AND OPERATION .

If applicable, Starting System - GTDI 2.0L Petrol - DESCRIPTION AND OPERATION .

A primary battery is located in the luggage compartment floor in a plastic molded tray and secured with a metal rod. The secondary battery is located in the DBJB (Dual Battery Junction Box).

The primary battery is a 90Ahr, 850A CCA AGM Battery
The secondary battery is a 14Ahr, 200A CCA Absorbed Glass Mat (AGM) Battery.

A BMS (Battery Monitoring System) control module is mounted on the primary battery negative terminal. The BMS control module is integral with the battery negative cable and is controlled by the GWM (Gateway Module).

CAUTION: To avoid damaging the BMS control module, always use the ground (negative (-)) terminal stud point on the right side top mount. Never connect directly to the primary battery negative terminal when connecting a slave power supply to the vehicle, the BMS control module can be damaged.

If a new primary battery is fitted to the vehicle, the BMS control module will require re-calibrating using a Jaguar approved diagnostic system.

When the vehicle leaves the factory, a transit relay is fitted to the battery positive terminal. The transit relay is connected to the CJB which limits the electrical functions to essential items only, to reduce loads on the primary battery. The transit relay must be removed from the vehicle during the PDI (Pre-Delivery Inspection). For additional information, refer to the PDI information.

The primary battery provides power to the BJB. The BJB contains three megafuses, delivering power to the RJB, the EJB and the starter motor and generator. In addition to containing fuses and relays, the RJB and CJB contain software to control a number of vehicle systems. These functions are covered in the appropriate service information.

A jump start terminal is located adjacent to the EJB. A cover protects the terminal when not in use. If jump starting is required, the cover must be removed and the positive (+) jump lead attached securely.

The negative (-) jump lead is attached to a stud located on the right side top mount in the engine compartment. The cover must be fitted to the positive terminal when not in use.

Dual Battery System

The dual battery system is used on vehicles with the stop/start system. The dual battery system prevents the vehicle electrical systems being subjected to undesirably low voltages during repeated engine restarts. If the electrical systems are subject to low voltages the customer may notice degraded performance of components and systems and incorrect fault DTC's (Diagnostic Trouble Codes) may be stored.

The dual battery system isolates all electrical components and systems sensitive to low supply voltage from the primary battery while an engine start is in progress, and supplies them from the secondary battery. Without the dual battery system, the electrical power required by the TSS (Tandem Solenoid Starter) motor to crank the engine for each start would cause a voltage drop across the entire vehicle electrical network, and cause control modules to function incorrectly and in some cases reset and/or record DTC's.

If the dual battery system is unable to prevent electrical supplies to the vehicle systems being subjected to low voltage levels during engine stop/start operations, due to the condition of the primary and/or secondary batteries or a system fault, the stop/start feature is disabled.

The dual battery system comprises the following components:

Dual Battery Module (DBM)
Dual Battery Junction Box (DBJB)
Gateway Module (GWM)
Primary battery
Secondary battery.

The GWM hosts most of the software required to control the dual battery system and components. The GWM monitors the components and can store fault related DTC's.

The GWM also controls the charging system software in conjunction with the ECM, RJB, CJB and ABS (Anti-lock Brake System) control module via the high speed and medium speed CAN (controller area network) bus. The GWM software will monitor the status of the stop/start system and determine when a stop/start event can occur. It can also intervene to maintain vehicle systems by keeping the engine running or initiating a restart due to, for example, climate control system requirements or request for restart from the ECM. A brake pressure signal is received from the ABS control module which will indicate to the GWM that an engine restart is required from driver operation of the foot brake.

The GWM contains the intelligent power management system and the BMS software. Monitoring of the primary battery condition for stop/start is controlled by the GWM and the BMS control module.