OBD-II trouble code
U0111: Lost Communication with Battery Energy Control Module A
A module on the network can no longer hear from battery energy control module A. Usually a power, ground, or wiring fault — and because this module manages the high-voltage battery, a hybrid or EV may cut power, refuse to charge, or not enter Ready mode.
Quick facts
- System
- Network
- Category
- Network Communication
- Severity
- High severity
- Drivable
- No — stop driving until repaired
- Repair cost range
- $150 – $2,000
- DIY difficulty
- Shop recommended
What does U0111 mean?
U0111 is set when another module on the vehicle's communication network — usually a hybrid or vehicle control module — stops receiving messages from battery energy control module A, commonly called the battery management system (BMS). On hybrid and electric vehicles this module monitors the high-voltage battery pack: it tracks cell voltages, temperature, and state of charge, manages cooling, controls the main contactors, and reports the battery's condition back over the network. When the network loses contact with it, U0111 records the dropout.
The causes follow the familiar communication-code pattern. The module may have lost low-voltage power or ground through a blown fuse, corroded ground, or failed relay. The communication wiring or connector at the module can be damaged or corroded. The module's internal communication circuitry can fail, or another module on the bus can disrupt communication for everyone. Low 12-volt system voltage can also cause intermittent dropouts. Because this module manages the high-voltage battery, diagnosis must follow the manufacturer's high-voltage safety procedures.
Because safe use of the high-voltage battery depends on this module, the symptoms are usually severe. The vehicle may refuse to enter Ready mode, decline to charge, enter reduced-power or fail-safe mode, or disable hybrid/electric drive entirely; warning lights and 'service high-voltage system' messages are common. The check engine light or hybrid/EV warning comes on, often with companion battery-system codes. Because the battery management module is a safety guardian for a high-energy system, U0111 should not be ignored — and the high-voltage components make this a job for a qualified hybrid/EV technician.
Common causes
- Blown low-voltage power or ground fuse for the battery energy control module
- Corroded or loose ground at the module
- Damaged communication wiring to the battery energy control module
- Corroded or backed-out terminals at the module connector
- Failed internal communication circuitry in the module
- Another module on the bus disrupting network communication
- Low 12-volt system voltage from a weak auxiliary battery
- High-voltage battery or pack-harness fault detected by the module
Symptoms
- Vehicle won't enter Ready mode or won't start the drive system
- High-voltage battery won't charge or charging stops early
- Reduced-power or fail-safe mode; loss of hybrid/electric drive
- Hybrid/EV warning light and 'service high-voltage system' message
- Check engine light on, often with battery-system codes
- Scan tool can't communicate with the battery energy control module specifically
- Symptoms may be intermittent with a marginal connection
Diagnostic steps
- 1.Scan all modules; confirm the battery energy control module is the one that's unreachable while others respond.
- 2.Follow the manufacturer's high-voltage safety procedures before working near the battery pack.
- 3.Check the module's low-voltage power and ground fuses and the relevant relays.
- 4.Inspect the module ground and communication connector for corrosion, looseness, and damage.
- 5.Measure the communication bus lines at the module connector and verify continuity back to the bus.
- 6.Test the 12-volt auxiliary battery and charging, since low voltage can cause intermittent communication loss.
- 7.If power, ground, and wiring are good but the module still won't communicate, the module is the likely failure and will need replacement and programming by a qualified hybrid/EV technician.
Repair cost
$150 – $2,000
A blown fuse, corroded ground, or connector repair is the cheapest fix at $150-$400 once located. Wiring repair runs $250-$700. Diagnostic time commonly adds $200-$400 given the high-voltage safety steps. Replacing a battery energy control module / BMS is the most expensive outcome at $800-$2,000 or more including programming, and is a last resort after cheaper causes are ruled out. This work should be done by a qualified hybrid/EV shop.
Estimate your repair
Run the numbers for your vehicle
Open the Repair Cost Estimator with module communication / can bus diagnosis preselected. Adjust labor rate and vehicle category to fit your situation.
DIY vs shop
Leave this one to a qualified shop. It typically involves emissions-critical components, refrigerant handling, or other work that requires manufacturer-grade tooling, training, or certification. DIY attempts often produce a more expensive problem than the original code.