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 8

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 8
  • 1Air conditioning controller internal gateway forwarding function failure or software fault prevents correct relay of the BMS 0x44A message.
  • 2Poor contact, open circuit, short circuit, or abnormal terminating resistor in the CAN_H/CAN_L wiring harness between the BMS and A/C controller (Powertrain CAN) or between the A/C controller and BCC (Body CAN)
  • 3An internal BMS control module fault causes an abnormal 0x44A message transmission cycle or stops transmission.
  • 4Poor power supply (12V constant/ignition power) or ground connection to relevant control modules (BMS, A/C controller, BCC), causing communication signal level drift.
  • 5Backed-out, oxidized, loose, or broken pins in CAN network connectors (such as BJG02, GJK04, and MPC).
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). 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), and verify the ground points are secure. Measure the ground resistance; it must be less than 1Ω. Inspect the 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 approx. 0 V) and termination resistance (measure with power off: normal is approx. 60 Ω; a 120 Ω reading indicates an open circuit).
  • 4
    Inspect 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 backed-out pins, oxidation, looseness, or broken pins (such as broken pin 15 in Case 3).
  • 5
    Use a CAN analyzer or oscilloscope to capture bus data and 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, update the air conditioning controller or BMS software. If the fault persists, replace the air conditioning controller (gateway function integrated unit) first. Finally, 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 8 Fault Codes
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.B1109DTC B1109 indicates an open circuit in the communication line between the air conditioning system PM2.5 air quality sensor (dust concentration sensor) and the air conditioning control unit (AC ECU), or an open circuit within the sensor internal circuitry. Typically located in the air conditioning intake duct, this sensor monitors real-time PM2.5 particle concentration inside and outside the vehicle. It provides data to the automatic air conditioning system for intelligent switching between fresh air and recirculation modes and for controlling the air purification device. During an open circuit fault, the AC ECU cannot receive the air quality signal, triggering the system fail-safe mode. Symptoms typically include failure of the automatic recirculation function, abnormal air purification indicator light operation, or abnormal air quality data displayed on the air conditioning panel. Severe cases may compromise the cabin environment control strategy, but do not directly affect vehicle driving safety.B110A02DTC B110A02 indicates the thermal management master control unit (HVAC ECU) or body control module (BCM) failed to receive valid CAN data frames from the PM2.5 air quality sensor over consecutive communication cycles (typically 500ms per cycle). The sensor typically mounts at the HVAC unit air inlet or behind the glove box and transmits real-time particulate concentration data (unit: μg/m³) to the HVAC controller via the CAN bus. The fault is essentially a communication link layer timeout. Potential causes include physical layer wiring faults, sensor power supply failures, sensor internal MCU lockup, or CAN network topology damage. Although this non-critical fault does not directly affect driving safety, it disables the intelligent air purification strategy and the automatic fresh air/recirculation switching function. In extreme cases, it triggers a thermal management system degraded mode, limiting compressor power or fixing the air flap position.B110B07This fault code indicates abnormal operation of the internal air pump (sampling pump) in the PM2.5 air quality detection module. The PM2.5 detector uses the laser scattering principle to measure particulate concentration and requires a built-in air pump to draw ambient air into the detection chamber at a constant flow rate. The ECU sets this code when it detects an open or short in the air pump drive circuit, abnormal current (stall or free-running), or abnormal speed feedback. This fault causes the automatic air conditioning system to lose air quality sensing capability, preventing automatic switching between fresh air and recirculation modes. The instrument cluster air quality display may show '--' or a fixed value, but the fault does not affect the vehicle powertrain or basic air conditioning cooling and heating functions.B173CDTC B173C indicates the Supplemental Restraint System (SRS) detects the Right Second Row Side Airbag squib circuit resistance exceeds the calibrated threshold (typically >4.5Ω). This fault is an active diagnostic result of the SRS system, indicating a high-resistance condition in the circuit between the Airbag Control Unit (ACU) and the airbag module. Causes for excessive resistance include increased contact resistance, a partially broken wiring harness, terminal oxidation, or an aging squib wire inside the airbag module. This fault causes the system to mark the airbag circuit as 'unreliable', meaning the airbag may fail to deploy during a collision. The fault typically illuminates the instrument cluster airbag warning light (SRS light) continuously, and some models also sound a warning buzzer.
Common problems reported for Atto 8 →Atto 8 overview →
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.