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) — Qin Plus

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 — Qin Plus
  • 1Air conditioning controller internal gateway forwarding function failure or software abnormality 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 A/C controller (Powertrain CAN), or between the A/C controller and BCC (Body CAN)
  • 3An internal fault in the BMS control module causes an abnormal 0x44A message transmission cycle or stops transmission.
  • 4Poor power supply (12V constant power/ignition power) or ground connection of the relevant control modules (BMS, A/C controller, BCC), causing communication signal level drift.
  • 5Backed-out terminals, oxidation, looseness, or broken pins at CAN network connectors (such as BJG02, GJK04, and MPC connectors).
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 the 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 tight. Measure the ground resistance (must be less than 1Ω). Specifically inspect the body control 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; expected value is 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 there are 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. Confirm the BMS sends 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 air conditioning controller or BMS software. If the fault persists, replace the air conditioning controller (integrated gateway module) 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 Qin Plus Fault Codes
B1108For 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.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.B110913DTC B110913 indicates an open signal circuit for the PM2.5 rapid detector (in-cabin air quality sensor). This sensor typically mounts inside the air conditioning system intake duct. It monitors in-cabin PM2.5 concentration in real time and provides data to the automatic air conditioning system for intelligent control of the air purification function. The BYD diagnostic protocol uses sub-code '13' to specifically indicate an open signal circuit. Although this fault theoretically affects a comfort feature, BYD Qin series vehicles classify it as a Level 3 (severe) fault. This classification occurs because the air conditioning system interacts with the battery thermal management system (e.g., monitoring battery cooling intake air quality). The fault can disable the automatic air conditioning mode and prevent the air purification function from operating. In extreme cases, it affects the battery compartment intake air quality assessment, triggering the 'repair immediately' strategy.B110AThis DTC indicates interrupted CAN bus communication or abnormal data between the air conditioning control unit (ACU) and the PM2.5 air quality sensor. The PM2.5 sensor monitors particulate concentration inside and outside the vehicle and provides the basis for purification control in the automatic air conditioning system. The ACU triggers this fault if it fails to receive a valid CAN message from the sensor within the specified period (usually 100-500 ms), if message verification fails, or if the signal frame times out. Although this fault does not affect vehicle driving safety, it disables the automatic air purification function. The air conditioning system cannot automatically switch between recirculation and fresh air modes or activate the air purification mode based on air quality. A persistent fault may restrict the thermal management strategy.
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.