U0111: How to Diagnose & Fix — Lost Communication With Battery Energy Control Module "A"
7 vehicles · 4 makes · $180-$600 repair
How to diagnose and fix U0111: most-reported vehicles
Ranked by owner reports. Each card gives the symptoms, how to confirm the cause, the fix, parts and sources for that vehicle.
Polestar Polestar 2 · 2021–2022
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 23, 2021, with owner letters mailed April 23, 2021. This is the battery-management-side power-loss campaign and is separate from both the front inverter capacitor tin-plating recall and the later BMS charge-limit software campaign — a single car can be open on more than one.
Common Symptoms
- Sudden total loss of drive power while driving
- 'Reduced propulsion performance' or stop-safely-now warning on the driver display
- Car will not move from a stop and shows a high-voltage system fault
- High-voltage system shuts down while 12V accessories still work
- Fault clears after a full power cycle, then recurs
How to Fix
Free recall remedy: BECM software update, delivered either over the air or by a Polestar service point. Verify by VIN at nhtsa.gov/recalls rather than assuming an OTA landed — early cars that sat on lots or had connectivity problems did not always take the update. If a car still drops the HV system after the update, the contactor assembly and the BECM itself need to be scanned; a genuine contactor or BECM hardware failure is a warranty repair under the 8-year/100,000-mile HV battery coverage.
Sources for this issue (3)
Volvo XC40 · 2021–2022
In the XC40 Recharge BEV the Battery Energy Control Module (BECM) supervises the traction pack contactors. A microprocessor fault causes the BECM to reset while driving; on reset it opens the high-voltage contactors as a fail-safe, instantly disconnecting the traction battery from the drive units. The result is an abrupt, total loss of propulsion at speed with no warning — the car coasts, power steering and brake assist remain but regen and drive are gone. This is distinct from the well-known 12V accessory-battery no-start: here the 12V system is fine and the vehicle is already moving. NHTSA campaign 21V109000 covers 2021-2022 XC40 Recharge.
Common Symptoms
- Sudden complete loss of drive power while driving
- Vehicle coasts to a stop with no propulsion
- Red 'stop safely' / propulsion system service warning
- Vehicle restores power after a full shutdown and restart
How to Fix
Free BECM software update at a Volvo dealer under recall 21V109000 (remedy available March 30, 2021). If the fault recurs after the update, the dealer should pull traction-battery fault memory — repeat contactor-open events on updated cars have been traced to a failing BECM or a high-resistance HV connector at the pack rather than software.
Call to confirm they can assess your vehicle and perform the stated work. Search results do not confirm qualification, eligibility or coverage.
Sources for this issue (1)
Mercedes-Benz EQE · 2023–2025
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.
Common Symptoms
- Sudden loss of drive power while driving
- "Drive system: Stop safely" or "Drive system fault" message
- Vehicle will not restart after shutdown
- Red HV battery warning on cluster
- Vehicle coasts to a stop in traffic
How to Fix
Dealer reflash of the battery management system control unit under recall 24V-372 (MBUSA number 2024050004 family). This remedy is NOT deliverable over the air — the car must go to a Mercedes dealer for a XENTRY flash. If the car has already stranded, a XENTRY soft reset restores drive, but the software update is the permanent fix. Check VIN at nhtsa.gov/recalls.
Sources for this issue (3)
Mercedes-Benz EQS · 2022–2025
Mercedes-Benz GLB · 2024–2026
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U0111 code reference
General diagnostic-code context. The code alone does not confirm a cause for your vehicle; use the applicable issue card and its sources.
Frequently asked questions
What does U0111 mean?
U0111 stands for "Lost Communication With Battery Energy Control Module "A"." Sets when a module loses data-bus communication with Battery Energy Control Module 'A' (the high-voltage battery management controller) and no longer receives its expected messages.
What are the most common causes of U0111?
The most common causes of U0111 are: Open or shorted bus wiring to the battery energy control module, Corroded or loose connector / poor ground, Blown fuse / lost low-voltage power feed, Low 12V battery voltage, Failed battery energy control module. The specific cause varies by vehicle.
How much does it cost to fix U0111?
Repair costs for U0111 range from $180 to $600, depending on the vehicle and root cause.
Which vehicles are affected by U0111?
Au7o has documented U0111 across 7 vehicle models from 4 manufacturers: Mercedes-Benz, Polestar, Volkswagen, Volvo.
Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.