AU
B185014

This fault code indicates a short to ground or open circuit in the rear HVAC blower motor speed control signal circuit — Seal U

Thermal Management System

This fault code indicates a short to ground or open circuit in the rear HVAC blower motor speed control signal circuit.

Modern BYD vehicles typically use a PWM (pulse-width modulation) signal or an analog voltage signal (0-5V/0-12V) for stepless rear blower speed control.

The HVAC ECU triggers this fault code when it detects an abnormal control signal voltage (a constant 0V short to ground or a high-impedance open circuit) to the rear blower speed control module (power transistor) or blower motor.

This fault results in no airflow from the rear HVAC vents, prevents fan speed adjustment, or restricts operation to a fixed fan speed.

In extreme cases, it triggers the HVAC thermal management protection and limits battery or motor cooling capacity, classifying this as a severe fault.

5
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Internal breakdown of the rear blower speed control module (Power Transistor), causing the control signal wire to short to ground.
  • 2Internal short circuit in the rear blower assembly motor pulls down the control signal voltage.
  • 3Harness wear or crushing: Damaged wiring harness insulation at the front seat rails, under the carpet, or in the centre tunnel shorts the signal wire to body ground.
  • 4Loose or corroded connector: The blower motor connector (usually marked BK45/BK46, etc.) located in the B-pillar, under the rear seat, or inside the air conditioning duct has poor contact, backed-out terminals, or water ingress causing oxidation, resulting in an open circuit.
  • 5Air conditioning controller (HVAC ECU) internal drive circuit fault prevents output of a normal PWM speed control signal.
What To Do
  • 1
    Read freeze frame data: Use the BYD VDS diagnostic tool to record vehicle speed, ambient temperature, and blower duty cycle data at the time of the fault. Confirm whether the fault is continuous or intermittent.
  • 2
    Visual inspection: Remove the rear center console or roof air conditioning control panel (depending on vehicle configuration). Inspect the rear blower assembly for abnormal noise, binding, or burn marks. Check for detached wiring harness retaining clips.
  • 3
    Circuit measurement: Disconnect the blower speed control module connector and measure the resistance to ground of the control signal wire (usually a thin wire, possibly blue/green/yellow). A resistance of less than 5Ω indicates a short to ground. Infinite resistance and no continuity to the ECU terminal indicate an open circuit. Check the blower power supply (constant power) and ground circuits.
  • 4
    Component isolation test: Bypass the blower control module and supply power directly to the blower motor to verify smooth operation. Use an oscilloscope to measure the PWM waveform output from the A/C controller (normal: square wave with fixed frequency and variable duty cycle).
  • 5
    Wiring harness repair and replacement: If the wiring harness shows wear, repair it with heat-shrink tubing and re-secure the routing. If the speed control module or blower motor is damaged, replace the rear blower assembly (spare part numbers vary by vehicle model, e.g., 8102010-X00 for Song MAX). After replacement, perform A/C system self-learning and matching (required on some models).
  • 6
    Verification: Clear the fault code. Using the diagnostic tool active test, adjust the rear blower speed from 0% to 100% and verify the data stream changes normally. Perform a 30-minute road test to confirm the fault does not recur.
Real-World Cases
BYD DTC AI Analysis

Song MAX rear AC suddenly lost airflow; wiring harness chafed and shorted to ground.

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Vehicle: 2018 Song MAX DM, 42,000 km. Symptom: Instrument cluster showed thermal management system warning after turning on the rear AC. Retrieved DTC B185014. Diagnosis: Removed rear seats and centre console trim. The rear blower motor sits beneath the third-row seats. The seat rail mounting bracket had crushed the speed control signal wire (yellow/green), breaking the insulation and causing a short to ground. Measured 0.8 Ω between signal wire and ground. Repair: Cut out the damaged section, soldered in an extension and sealed it with double-layer heat-shrink tubing. Rerouted the harness clear of the seat rail travel path and secured it high on the body with cable ties. Replaced the rear blower speed control module (damaged by the short circuit). Cleared the DTC and verified the rear fan operates correctly on all speed settings.
BYD DTC AI Analysis

Qin EV rear blower motor runs only at high speed; speed control signal open circuit.

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Vehicle: 2019 Qin EV High Range Edition. Fault: Rear AC blower runs at maximum speed only; speed cannot be adjusted. DTC B185014 (intermittent) stored. Diagnosis: Per the wiring diagram, the rear blower speed control module is located at the rear of the center console. Inspection of connector BK45 revealed pin 2 (PWM control signal) had backed out; the terminal detached with light tension, causing an intermittent open circuit. Road vibration caused the pin to withdraw. Repair: Repaired the connector pin retainer, confirming the pin seated with a crisp click. Applied conductive grease to treat terminal oxidation. Cleared the DTC and performed an active test with the scan tool to verify PWM duty cycle varies linearly between 10–90%. Fault resolved.
BYD DTC AI Analysis

Tang DM rear blower noisy then faulted; motor short-circuited and damaged the speed control module.

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Vehicle: 2019 Tang DM, 68,000 km. Symptoms: The rear air conditioner first developed a buzzing noise, then stopped working completely. The instrument cluster displayed a cooling system fault. Diagnosis: Retrieved DTC B185014 (current fault). Removed the rear overhead AC assembly (the Tang DM uses a ceiling-mounted rear unit). Found the blower impeller jammed with children's toy fragments. Attempting to rotate the motor revealed significant resistance and excessive current draw. Measured the blower motor resistance at only 1.2Ω (normal: 3–5Ω), indicating an internal short. Further testing at the speed control module output showed the control signal shorted to ground; the motor short-circuit current surge had damaged the speed control module's power transistor. Resolution: Replaced the rear blower assembly (motor and impeller) and the blower speed control module (located inside the air duct). Cleared foreign objects from the air duct. Post-repair testing confirmed smooth operation at all speed settings and the fault code cleared.
BYD DTC AI Analysis

Internal fault in Song MAX HVAC controller caused rear blower motor control failure.

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Vehicle: 2017 BYD Song MAX petrol variant. Fault symptoms: Front AC operates normally, rear blower inoperative, DTC B185014 stored. Diagnostic procedure: Measured signal line voltage at the rear blower speed control module: constant 0 V (should vary 0–12 V). Wiring harness continuity tested normal; ground resistance infinite (no short). Inspected AC controller output terminals and found the PWM output pin for the rear blower showed no waveform (oscilloscope displayed a flat 0 V line). Front blower control operates normally, confirming partial controller function. Isolated the fault to the rear blower drive circuit inside the controller (likely MOSFET breakdown). Solution: Replaced the AC controller assembly (required programming to match vehicle VIN and configuration codes). After replacement, performed AC system initialization learning (via scan tool or specific button combination). Fault cleared; rear AC operation restored.
BYD DTC AI Analysis

Qin EV rear AC failed after driving through water; connector corroded

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Vehicle: 2019 Qin EV, fault after wading. Symptoms: Day after wading, coolant overheat warning light came on with AC running. Retrieved DTCs B185014 and B2A2F09 (thermal management). Diagnosis: Found rear AC intake near rear wheel arch. Water level exceeded door sill during wading, letting water into intake duct and soaking blower motor and connector under rear floor. Connector BK46 showed internal green copper corrosion; trace water between pins shorted control signal to ground (~200 Ω). Resolution: Dried AC ducts thoroughly with compressed air and heat gun. Replaced connector (or cleaned and treated with electrical contact cleaner). Replaced rear blower assembly (motor had water ingress, abnormal noise). Checked AC system sealing. Repaired water entry path through damaged rear wheel arch liner.
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.