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) — Seal 6 EV

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.

The U011187 fault code on the Seal 6 EV indicates a medium-severity communication fault where the Body Control Computer is not receiving battery status data from the BMS through the air conditioning controller. Common causes include a gateway/software fault in the A/C controller or damaged, loose, open, or shorted CAN wiring. Visit an authorised dealer for diagnosis and repair. Typical repair cost data is available from recorded cases.
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Cases Logged
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Causes
Likely Causes — Seal 6 EV
  • 1Air conditioning controller internal gateway forwarding failure or software fault prevents the controller from correctly relaying the BMS 0x44A message.
  • 2Poor connection, 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)
  • 3Internal 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 poor ground at related control modules (BMS, air conditioning controller, BCC), causing communication signal level drift.
  • 5Backed-out terminals, oxidation, looseness, or broken pins in 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 freeze frame data and environmental conditions at the time of the fault.
  • 2
    Check the power supply voltage of the BMS, A/C 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-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; resistance 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 harness GJK04 and instrument panel 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 analyser or oscilloscope to capture bus data. Verify the BMS sends message 0x44A (typical cycle: 10-100 ms) 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 (integrated gateway function 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 Seal 6 EV 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.B1737DTC B1737 indicates the Supplemental Restraint System (SRS) detected abnormal continuity between the right middle-row side airbag squib circuit (typically the second-row right seat side airbag or right curtain airbag) and the vehicle power supply (B+, battery positive). The SRS ECU monitors the airbag inflator resistance via an internal current source (normal resistance: 2.0–3.0 Ω). If the ECU detects the voltage across the inflator circuit remaining close to battery voltage (>5 V and approaching 12 V) instead of the expected low potential or floating state, it identifies a short to power. This fault prevents the airbag from deploying normally during a collision because the short circuit bypasses the firing current. In extreme cases, abnormal current can cause unintended deployment, posing a severe safety hazard.B173BDTC B173B indicates an abnormal electric A/C compressor speed feedback signal or a communication fault between the compressor controller and the motor. In BYD new energy models (e.g., Tang, Song, Qin, and Yuan series), this DTC belongs to the HVAC subsystem within the Body Control system and specifically involves the electric compressor closed-loop control circuit. The ECU sets this DTC when the compressor controller (IPM) fails to receive a valid pulse signal from the Hall speed sensor for more than 3 continuous seconds, or when the deviation between the detected actual speed and the target commanded speed exceeds the calibrated threshold (typically >500 rpm). This fault forces the A/C system into fail-safe mode and stops compressor operation. Symptoms include a complete lack of cooling, intermittent cooling, or a sharp decrease in cooling performance. The instrument cluster A/C warning lamp may also illuminate. Prolonged operation with this fault can degrade high-voltage system insulation or cause controller overcurrent damage.
Common problems reported for Seal 6 EV →Seal 6 EV 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.