AU
U016487

ISO 15031 defines fault code U0164 as 'Lost Communication With HVAC (Air Conditioning Control Module)' — Seal U

Thermal Management System

ISO 15031 defines fault code U0164 as 'Lost Communication With HVAC (Air Conditioning Control Module)'.

Sub-code 87 is a BYD-specific identifier indicating the BCC (Battery Cooling Controller/Body Control Computer) failed to receive key CAN messages from the air conditioning controller within a 500ms monitoring cycle: ID 0x1DB (ambient temperature, soft shutdown request) or 0x3CF (cabin compressor speed request, A/C request status).

This fault indicates a communication interruption between the HVAC sub-network (HVAC-CAN) and the Powertrain CAN or BMS network.

This interruption prevents the thermal management system from coordinating the electric compressor, PTC heater, and battery cooling circuit.

The system may trigger thermal management derating protection (power limitation or A/C disabled), but typically does not cause immediate vehicle immobilization.

5
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Abnormal HVAC controller power supply: Includes a blown F1/15 fuse or burnt terminals in the instrument panel fuse box, a backed-out pin or poor connection on the IGN ignition signal wire, or a loose ground wire, causing intermittent power loss to the module.
  • 2CAN bus physical layer fault: short or open circuit in A/C sub-network CAN-H and CAN-L lines, terminating resistance deviation (normally approx. 60Ω), or wiring harness chafing and insulation damage at the instrument panel frame bend.
  • 3HVAC module hardware fault: internal PCB water ingress and corrosion (often due to blocked A/C drain pipes causing condensate backflow), CPU or CAN transceiver chip damage, software version mismatch (protocol conflict after an OTA update).
  • 4Gateway communication interference: Gateway module fault between the powertrain network and comfort network causes cross-network message forwarding failure.
  • 5Wiring harness connector issue: Backed-out pins, oxidation, corrosion, or excessive contact resistance (>5Ω) at connector B09 (white 20-pin) or B10.
What To Do
  • 1
    Use the VDS2000/3000 diagnostic tool to read complete DTCs. Check for accompanying U0140 (lost communication with BCM) or B12C2 (compressor controller fault). Read the data stream to confirm HVAC module online status and communication voltage.
  • 2
    Check the HVAC controller power supply: measure the voltage across fuse F1/15 in the fuse box (should be 12V±0.5V), check the IGN signal wire voltage stability under vibration (should be >11V), and measure the ground resistance (should be <1Ω).
  • 3
    Check the CAN bus: Disconnect the HVAC connector. Measure the voltage to ground at OBD pin 6 (CAN-H, 2.5-2.7V) and pin 14 (CAN-L, 2.3-2.5V). Measure the terminal resistance (with power off, resistance at the HVAC connector should be 120Ω; total vehicle parallel resistance should be approximately 60Ω).
  • 4
    Physical connection check: Remove and inspect the HVAC module connector behind the glovebox. Check if B09 pin 5 (IGN) has backed out. Inspect the wiring harness for interference or wear against the metal dashboard frame. Check the connector for water stains or green oxidation.
  • 5
    Software diagnosis: Compare the HVAC module software version with the latest technical bulletin. Check if the head unit OTA upgrade caused a protocol mismatch. If necessary, use VDS to perform 'Air Conditioning Controller Programming' and 'Air Flap Self-Learning'.
  • 6
    Drainage system inspection: Check the air conditioning drain hose for blockages (common during poplar fluff season), inspect the evaporator housing sealing, and check the HVAC module mounting location for signs of water accumulation.
  • 7
    Component replacement and calibration: If confirming module hardware damage, replace the HVAC controller (part number HA-8121100). Perform 'Air Conditioning System Configuration' to write the vehicle VIN code, then perform 'Compressor Run-in' and 'Temperature Air Flap Calibration'.
Real-World Cases
BYD DTC AI Analysis

Song Pro DM climate control panel black screen; IGN signal pin backed out

✓
Symptoms: Air conditioning suddenly stopped working while driving. Multimedia display showed black screen or 'communication fault' on climate interface. VDS retrieved DTC U016487. Other functions normal. Diagnosis: CAN voltage at OBD port measured normal. Removed and inspected HVAC module inside centre console. Found pin 5 (IGN signal) of B09 connector (white, 20-pin) had backed out. Voltage dropped below 3 V over bumps, causing module to drop offline. Resolution: Re-crimped terminal and applied conductive adhesive. Secured wiring harness with cable ties to prevent chafing against dashboard frame. Cleared fault codes. Communication restored.
Original source ↗
BYD DTC AI Analysis

e5 450 ride-share: Burnt fuse holder with poor contact

✓
Symptoms: AC fails randomly, restores after restarting the vehicle, more frequent in hot weather. B12C2 fault code present. When the fault occurs, blower speed stays fixed but cannot be adjusted. Diagnosis: Live data showed the HVAC module dropping offline intermittently. Inspected the dashboard fuse box and found the F1/15 fuse pin burnt; measured contact resistance at 8.5Ω (abnormal). Discovered an aftermarket dash cam power tap had deformed the fuse box base. Repair: Replaced the dashboard fuse box assembly. Removed the aftermarket power feed wiring. Disconnected the battery negative terminal for 5 minutes to reset the HVAC module. Recalibrated the air door positions.
Original source ↗
BYD DTC AI Analysis

Qin Plus EV module damaged by water ingress after OTA update

✓
Symptoms: After the head unit OTA update, the AC system logged DTC U016487 and the code wouldn't clear. The system kept blowing hot air, the AC switch flashed, and the display showed "System Initialization Failed". Diagnosis: The HVAC software V1.02 didn't match the head unit V2.15 protocol. The module didn't respond to programming attempts. Removed the module and found visible water damage on the PCB from backflow due to a blocked AC drain pipe. Resolution: Replaced the AC control module (HA-8121100), cleared the drain pipe, and ran VDS to execute "AC System Configuration", "Air Door Self-Learning", and "Compressor Break-in" procedures.
Original source ↗
BYD DTC AI Analysis

Qin Pro EV air conditioning subnet CAN bus lines chafed and shorted

✓
Symptoms: A/C won't turn on after rain or car washes. Cluster shows "Thermal Management System Fault". Codes: U016487 and multiple U01** series communication faults. Diagnosis: Checked HVAC connector: CAN-H shorted to ground (0V). Traced harness and found the HVAC subnet backbone inside the dash chafed through at the steering column mounting bracket. Rainwater caused the short. Resolution: Repaired harness (rewrapped with waterproof tape), rerouted and added securing clips, replaced corroded HVAC connector.
BYD DTC AI Analysis

Qin EV300 ambient temperature data abnormality causes communication timeout

✓
Symptoms: No HVAC heat after winter morning starts. DTC U016487 set (1DB message loss). Fault cleared when ambient temperature rose at midday. Diagnosis: Factory scan tool showed HVAC module online but 1DB message counter not incrementing. External temperature sensor wiring checked OK. Found dry solder joint on HVAC internal temperature sampling circuit; poor contact at low temperatures caused message transmission timeout. Repair: Replace HVAC control module, or return to factory for PCB repair (resolder temperature sampling circuit).
Other Seal U 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.