AU
B2A5B11

This DTC indicates the Passenger Side Floor Vent Temperature Sensor signal circuit shorts to body ground (GND) — Seal U

Thermal Management System

This DTC indicates the Passenger Side Floor Vent Temperature Sensor signal circuit shorts to body ground (GND).

In the BYD thermal management system, this sensor uses a negative temperature coefficient (NTC) thermistor.

During normal operation, it changes resistance between 2-10kΩ as the vent temperature changes, outputting a 0.5-4.5V analog voltage signal to the HVAC ECU.

A short to ground pulls the signal voltage near 0V.

The controller detects this abnormal signal, typically interpreting it as an excessively high temperature or a circuit fault.

This condition causes the following: 1) The passenger side floor vent closed-loop temperature control fails, potentially resulting in continuous maximum cooling or heating and affecting occupant comfort. 2) The air conditioning system enters fault protection mode and limits compressor speed.

In extreme cases, this affects the heat exchange efficiency of the battery pack thermal management circuit. 3) In extreme ambient temperatures, the incorrect temperature signal causes the thermal management system to miscalculate and trigger vehicle power limitation.

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Cases Logged
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Causes
Likely Causes — Seal U
  • 1Thermistor breakdown or packaging failure inside the temperature sensor body causes an internal short circuit between the signal and ground terminals.
  • 2Worn wiring harness insulation near the front passenger footwell air outlet (commonly below the A-pillar, at the evaporator housing edge, or at the floor harness retaining clip) causes the signal wire (usually yellow/black or white/black) to directly contact the vehicle body metal frame.
  • 3Bent pins, backed-out pins, or metallic foreign objects between pins in the air conditioning controller connector (such as G64, G65, or G22, depending on vehicle model), causing a short circuit between the signal pin and the ground pin.
  • 4A blocked or poorly sealed evaporator drain hose causes condensate to overflow into the sensor connector, creating a short circuit between pins or a short to ground (common in high-humidity areas or vehicles with uncleaned air conditioning systems).
  • 5During vehicle modifications (such as installing a passenger-side dashcam, routing wiring for a 360-degree surround-view camera, or fitting full-coverage floor mats), screws or clips pinch and damage the wiring harness, or the connector is not fully seated.
What To Do
  • 1
    Use the VDS2000 or VDS2100 diagnostic tool to read the air conditioning system data stream. Check the "Passenger Foot Outlet Temp" value to verify if it remains fixed at -40°C (below lower limit) or 150°C (above upper limit) and does not change when adjusting the air conditioning temperature.
  • 2
    Disconnect the temperature sensor connector (usually a 2-pin black waterproof connector) located on the lower passenger-side evaporator housing or footwell air duct. Use a multimeter to measure the resistance between the two pins on the sensor body. At 25°C, normal resistance is 2-10 kΩ (refer to the specific vehicle repair manual; e.g., Qin Pro is approx. 4.5 kΩ). Replace the sensor if the resistance is near 0 Ω or infinite.
  • 3
    Keep the sensor connector disconnected. Set the multimeter to the resistance setting and measure the resistance from the harness-side signal pin (usually the BN/Y or WH/BK wire) to body ground and to the ground pin. The normal reading is infinity (OL). If the multimeter shows continuity (<1Ω), this confirms a short to ground in the circuit.
  • 4
    Visually inspect the wiring harness routing below the front passenger A-pillar, the right-side center console frame, and the floor harness. Focus on contact points between the wiring harness and body metal edges, retaining clips, and sharp bracket edges. Inspect for insulation wear, burn marks, or exposed copper strands.
  • 5
    Remove the glove box or front passenger lower trim panel. Inspect the air conditioning controller (HVAC ECU) connector pins for bends, corrosion, push-out, water stains, or verdigris. Clean the pins with electrical contact cleaner and repair them as necessary.
  • 6
    If the wiring harness is damaged, cut out the damaged section, solder or crimp a new harness section, and apply dual-layer heat-shrink tubing (adhesive-lined inner layer) for insulation and waterproofing. If the sensor is damaged, replace it with a genuine temperature sensor (example part number: 81204-XXXXX; confirm based on the specific vehicle model).
  • 7
    Restore all electrical connections and clear the fault codes. Set the air conditioning to Foot Mode and adjust the temperature from LO to HI. Verify the temperature value in the data stream changes normally with the actual outlet air temperature (range approximately 0-80℃). Confirm no fault codes are present, then return the vehicle.
Real-World Cases
BYD DTC AI Analysis

Song MAX: Blocked evaporator drain caused sensor water ingress and short circuit

✓
Model: 2018 Song MAX DM, 32,000 km. Symptoms: After 10 minutes of A/C operation, the instrument cluster displayed "Thermal Management System Fault". The passenger footwell vent blew cold air continuously and would not adjust. Diagnosis: Scanned with VDS and retrieved DTC B2A5B11. Reviewed live data and found the passenger footwell temperature fixed at -40°C (abnormally low). Removed the passenger-side evaporator lower cover and found water inside the temperature sensor connector; the pins were oxidised and green. Further inspection showed dust had blocked the evaporator drain hose, letting condensate overflow onto the sensor mount. Fix: Cleared the drain hose, dried the connector with compressed air and sprayed electronic contact cleaner. Replaced the temperature sensor (pins too corroded to repair). After reassembly, live data returned to normal and temperature adjustment worked correctly.
BYD DTC AI Analysis

Qin Pro EV Wiring Harness Chafing Causes Short to Ground After Accident Repair

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Model: 2019 Qin Pro EV. Fault appeared after right front accident repairs. Symptoms: AC cannot auto-regulate temperature after repairs. VDS reports DTC B2A5B11. Diagnosis: Disconnected sensor; resistance measured normal (3.8kΩ@25℃). Harness-side signal line-to-ground resistance measured 0.3Ω, confirming short to ground. Traced passenger floor harness routing; found mounting bracket shifted during accident repairs. Harness rubbed against sharp body bracket edge, damaging insulation and allowing signal wire to contact body ground. Repair: Cut out damaged harness section (~15cm). Reconnected using waterproof crimp terminals. Wrapped with PVC tape and corrugated tubing. Rerouted harness to clear sharp edges. Fault cleared.
BYD DTC AI Analysis

Qin EV300 AC controller connector pins bent, poor contact

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Vehicle: 2017 Qin EV300, 85,000 km. Symptoms: With the AC in foot mode, the passenger footwell outlet was abnormally cold, and the 'motor overheating' warning light triggered falsely. Diagnosis: DTC B2A5B11. Sensor and harness resistance measured normal, but the fault appeared intermittently when wiggling the HVAC controller harness. Removed the lower centre console and inspected the HVAC controller connector (22-pin grey). Found pin 14 (temperature sensor signal, yellow wire) bent and contacting pin 13 (ground, black wire), causing a short. Repair: Used a specialised pin removal tool (M202) to straighten the bent pin. Checked the pin housing for cracks, applied conductive grease to ensure good contact, and reconnected and secured the harness. Fault resolved.
BYD DTC AI Analysis

Song MAX: Aftermarket floor mats pinched wiring harness, causing short circuit

✓
Model: 2019 Song MAX. Owner self-installed full-surround floor mats; fault appeared the next day. Symptoms: AC panel displayed "Check Air Conditioning System" and VDS reported DTC B2A5B11. Diagnosis: Sensor resistance read normal, but the signal wire at the sensor connector shorted to ground. The owner had secured the mats with metal clips that pierced the carpet and crushed the hidden AC temperature sensor harness underneath, damaging the signal wire insulation and causing a short to body. Solution: Removed the metal clips. Repaired the wiring by stripping the damaged insulation and applying heat-shrink tubing. Replaced them with plastic fixing clips. Rerouted the harness clear of the mat mounting area. Cleared the DTCs. System returned to normal.
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.