U0111: How to Diagnose & Fix — Lost Communication With Battery Energy Control Module "A"

The facelifted GLB (2024 onward) gained a 48-volt mild-hybrid system with a second-generation belt-driven starter-generator (RSG), so the car now depends on a small 48V lithium-ion battery for engine restarts, coasting, and recuperation in addition to the conventional 12V battery. Owners on the MBWorld GLB forum report repeated 12V battery discharge - dead or weak battery after short periods parked, requiring frequent jump starts or a tender. Mercedes-Benz opened service campaign 2025100004 (late October 2025) to update the 48-volt on-board electrical system battery software, because a communication error can occur when the 48V lithium-ion battery is reactivated during reinitialization; the same campaign covers CLA and GLA. Per the campaign bulletin, the system can store this error and illuminate the check engine (malfunction indicator) lamp unnecessarily; the bulletin does not link it to 12V battery drain. Separately, GLB owners across model years report the small 1.2 Ah auxiliary battery plus short-trip driving leaves the 12V battery chronically undercharged.

Other control units on the EVA2 platform continuously send diagnostic requests to the high-voltage battery management system (BMS). The BMS memory capacity overflows, the module shuts down and commands the HV contactors open, disconnecting the 90.6 kWh pack from the drive unit. The car loses propulsion without warning while driving; steering and brakes remain but power assist behavior changes. NHTSA campaign 24V-372 covers 14,912 EQE/EQS vehicles built roughly Feb 1 2023 - May 11 2024.

A fault in the BECM microprocessor operating system causes the processor to reset while the car is in operation. The reset drops the high-voltage contactors, disconnecting the traction pack from the drive units and producing an immediate loss of propulsion with no warning. NHTSA campaign 21V110000 (Polestar R10079) covered 3,457 US 2021-2022 Polestar 2 vehicles, reported February 24, 2021, with owner letters mailed April 23, 2021. This is the battery-management-side power-loss campaign and is separate from the 2020 front inverter capacitor tin-plating recall, which did not cover US cars.

The automatic engine Start/Stop system on the T-Cross is very sensitive to battery state of charge and to the battery management sensor. Owners report the Start/Stop function stopping working (error shown in the instrument cluster), and in some cases unexpected engine stalling, often relatively early in the car's life. Common root causes are a degraded 12V battery that no longer holds the capacity the system needs, or a faulty battery/intelligent-charging sensor feeding bad data to the engine control unit. The same sensitivity contributes to perceived parasitic battery drain on short-trip use.

Other control units on the EVA2 bus continuously send diagnostic requests to the high-voltage battery management system. The BMS memory overflows, the module shuts down, and the HV contactors open - disconnecting the 108 kWh pack from the drive unit. The result is an instant loss of propulsion at speed with the red turtle icon on the display, even with a nearly full state of charge. NHTSA recall 24V-372 covered 14,912 EQE/EQS sedans and SUVs, and owners reported the failure occurring on freeways before the fix.