AU
U011187

DTC U011187 indicates the Body Control Computer (BCC) failed to receive CAN message ID 0x44A (hexadecimal) from the Battery Management System (BMS) via the air conditioning controller (acting as a gateway/relay node) — Atto 3

Thermal Management System

DTC U011187 indicates the Body Control Computer (BCC) failed to receive CAN message ID 0x44A (hexadecimal) from the Battery Management System (BMS) via the air conditioning controller (acting as a gateway/relay node).

This battery status information frame typically contains key thermal management parameters, including total battery voltage, total current, SOC, highest/lowest cell voltage, and temperature.

This fault represents a gateway communication interruption between the thermal management sub-network and the body control network.

The interruption prevents the BCC from obtaining real-time battery status to coordinate thermal management actuators, such as air conditioning compressor speed, PTC heating, and cooling fans.

Consequently, this can cause battery temperature control failure, range estimation deviation, or abnormal coordination between the air conditioning system and battery cooling.

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Cases Logged
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Causes
Likely Causes — Atto 3
  • 1Air conditioning controller internal gateway forwarding function failure or software fault prevents the correct relay of the BMS 0x44A message.
  • 2Poor contact, open circuit, short circuit, or abnormal terminal resistance in the CAN_H/CAN_L wiring harness between the BMS and air conditioning controller (powertrain CAN), or between the air conditioning controller and BCC (body CAN).
  • 3Internal BMS control module fault causes an abnormal 0x44A message transmission cycle or stops transmission.
  • 4Poor power supply (12V constant power / ignition feed) or ground connection to relevant control modules (BMS, A/C controller, BCC), causing communication signal level drift.
  • 5CAN network connectors (such as BJG02, GJK04, and MPC connectors) have backed-out terminals, oxidation, loose connections, or broken pins.
What To Do
  • 1
    Use VDS2000 or the latest diagnostic tool to read all vehicle DTCs, check for accompanying U-class communication fault clusters (e.g., U0141, U0291), and record freeze frame data and environmental conditions at the time of the fault.
  • 2
    Check the power supply voltage to the BMS, air conditioning controller, and BCC (12V/B+ must be greater than 11V). Verify ground point tightness. Measure the ground resistance; it must be less than 1Ω. Inspect body control-related ground wires for burning or looseness.
  • 3
    Measure the powertrain CAN and body CAN bus voltages (CAN-H: 2.6–2.8 V, CAN-L: 2.2–2.4 V, static differential voltage approximately 0 V) and terminal resistance (measure with power off; the reading should be approximately 60 Ω. A 120 Ω reading indicates an open circuit).
  • 4
    Check the CAN line connectors between the air conditioning controller and the BMS, and between the air conditioning controller and the BCC (focus on key nodes such as floor wiring harness GJK04 and instrument panel wiring harness BJG02). Confirm no pins are backed out, oxidized, loose, or broken (such as broken pin 15 in Case 3).
  • 5
    Use a CAN analyzer or oscilloscope to capture bus data. Verify the BMS transmits message 0x44A (typical cycle: 10-100ms) and the air conditioning controller correctly forwards it to the BCC network.
  • 6
    If wiring and signals are normal, reflash the A/C controller or BMS software. If the fault persists, replace the A/C controller (integrated gateway unit) first, then consider replacing the BMS.
Real-World Cases
BYD DTC AI Analysis

BYD Tang ACC Fault with U011187 — Burnt Ground Wire with Loose Connection

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The ACC system failed and the instrument cluster displayed a communication error. Diagnosis revealed multiple communication faults including U011587 and U101387 in addition to U011187 (Lost Communication with BMS). Inspection of the MPC connector found the 5# ground wire bolt loose, causing the contact to burn. Grinding and retightening the ground point cleared the fault codes and restored ACC function. Poor grounding causes communication errors across multiple control modules, triggering U011187.
Original source ↗
BYD DTC AI Analysis

BYD e5 taxi intermittent loss of power while driving — VCU communication fault cluster

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The vehicle intermittently displayed "Check Powertrain System" while driving and the OK light went out; it recovered after powering off and waiting. VDS scan showed the Battery Manager reporting communication faults with the leakage sensor, active discharge module and A/C; the Drive Motor Controller reporting a communication fault with the Vehicle Control Unit; and the Vehicle Control Unit reporting U011187 (communication fault with Battery Manager), U012887, U029187 and over a dozen other communication faults. Checked the wiring harness connections at the Vehicle Control Unit; they were secure but CAN line integrity needs further troubleshooting.
Original source ↗
BYD DTC AI Analysis

BYD e2 intermittent failure to enter OK mode — broken CAN High pin in floor wiring harness

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Vehicle occasionally failed to enter Ready mode, with the cooling fan running continuously and difficulty shutting down. VDS detected multiple communication faults: U011187, U024E87, and U012187. Measurements of the Comfort and Powertrain CAN buses revealed abnormal termination resistance on the Powertrain network. Further inspection found that pin 15 (CAN High) of the floor harness GJK04 module had broken, causing an intermittent connection that left CAN High pin 5 of BJG02 without voltage. Repaired the CAN High circuit by bridging the break and restored the pin connection. Fault resolved.
Original source ↗
BYD DTC AI Analysis

BYD U011187 General Diagnosis — Comprehensive Analysis of Wiring and Module Faults

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DTC U011187 (Lost Communication With BMS) – General Diagnostic Procedure: Common causes include poor harness connections (loose or corroded vehicle wiring interrupting signal transmission), sensor failures (damaged vehicle status sensors affecting communication), and control module faults. Check all related harness connections for looseness or corrosion. Replace battery management sensors or the BMS control module as required. Clear the DTC with a diagnostic scan tool, then perform matching and relearn procedures.
Original source ↗
Other Atto 3 Fault Codes
P0A0DBattery Energy Control Module Requested MIL IlluminationP0AA6Hybrid Battery Voltage System Isolation FaultP1A00Drive Motor "A" Performance — BYD proprietaryB1108For the BYD Song MAX (2017–2019), DTC B1108 indicates a short circuit in the PM2.5 air quality detection module (dust sensor) or its wiring harness. The sensor uses laser scattering to detect in-cabin and outside PM2.5 concentrations and transmits data to the HVAC ECU via the LIN bus or an analog signal. Short circuit conditions include: 1) Sensor power supply wire (+5V/+12V) shorted to ground 2) Signal wire shorted to power or ground 3) Short circuit in the sensor's internal photoelectric detection circuit This fault prevents the automatic climate control from switching between fresh air and recirculation based on air quality. The system enters fail-safe mode (typically forced recirculation). Severe short-circuit current can destroy the HVAC ECU sampling circuit. The system classifies this as a Level 3 severe fault and restricts vehicle operation to prevent electrical fires or controller damage. For other BYD models (such as the Qin EV, E5, and Song DM), B1108 indicates a driver-side sunload sensor fault, reflecting differences in DTC definitions across models.B110811This DTC indicates a short circuit in the air conditioning system PM2.5 air quality sensor (rapid detector). Specifically, abnormal continuity exists between the sensor power supply circuit or signal output circuit and body ground or battery positive. This causes the control module (ACU/air conditioning controller) to detect abnormal current or a voltage signal outside the valid range (typically 0V or supply voltage). The PM2.5 sensor monitors internal and external particulate concentrations, providing the data the automatic air conditioning system uses to switch between fresh air and recirculation modes. A short circuit disables the air quality monitoring function. This fault may force the air conditioning system into recirculation protection mode and trigger related thermal management system faults, as the air conditioning system acts as a key actuator in vehicle thermal management. In severe cases, the short circuit current can damage the internal sampling circuit of the air conditioning controller or overheat the wiring harness.
Data confidence: Official This information is for reference only. Always consult a qualified technician for diagnosis and repair. Do not attempt high-voltage system repairs yourself.