AU
B2A5A11

This DTC indicates a short to ground in the signal circuit of the front passenger side FACE mode outlet air temperature sensor — Seal U

Thermal Management System

This DTC indicates a short to ground in the signal circuit of the front passenger side FACE mode outlet air temperature sensor.

In the BYD dual-zone automatic air conditioning system, this sensor uses an NTC (negative temperature coefficient) thermistor.

Under normal conditions, sensor resistance decreases as temperature increases (approximately 2 kΩ at 20°C).

The air conditioning controller calculates the actual outlet air temperature by detecting the voltage signal (typically in the 0-5 V range) through a voltage divider circuit.

When the signal wire shorts to the vehicle body ground, the controller detects a continuous voltage below 0.1 V (or close to 0 V) and sets DTC B2A5A11.

This disables the front passenger side temperature control.

The air conditioning system may enter limp mode and default to a fixed output temperature, reducing passenger comfort.

In extreme cases, false readings may trigger thermal management system protection.

3
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1The thermistor inside the temperature sensor breaks down and short-circuits, grounding the signal terminal directly.
  • 2Damaged wiring harness insulation inside the right dashboard A/C duct allows the signal wire to contact the metal duct or a sharp body edge, causing a short to ground.
  • 3Poor sensor connector sealing allows A/C condensate intrusion, causing a short circuit between pins or a short to ground.
  • 4A detached wiring harness retaining clip causes the harness to chafe against the instrument panel frame during driving, resulting in long-term wear damage.
  • 5Improper wiring harness routing after previous repairs caused the instrument panel trim to pinch the harness and puncture the insulation.
What To Do
  • 1
    Connect the VDS2000 or BYD dedicated diagnostic tool, read the fault codes to confirm B2A5A11 is a current fault, and record the ambient temperature value from the freeze frame data.
  • 2
    Remove the passenger-side lower dashboard trim panel and locate the face vent temperature sensor (usually inside the right HVAC assembly air outlet duct). Disconnect the connector and measure the sensor resistance: at 20°C, it should be 1.8-2.2 kΩ. If it reads 0-10 Ω, the sensor has an internal short circuit. Replace the sensor.
  • 3
    Leave the connector disconnected. Use a multimeter to measure the resistance between the harness-side signal pin (usually the yellow wire) and body ground. Normal resistance is greater than 10MΩ. If continuity exists, inspect the harness routing for damage. Focus on sharp edges, such as where the harness passes through the firewall and instrument panel bracket.
  • 4
    Check connector seal ring integrity. Inspect pins for oxidation, verdigris, or water marks. If necessary, clean with electronic contact cleaner and spray WD-40 for waterproofing. Replace the connector if severely corroded.
  • 5
    If the wiring harness appears normal but has a short to ground, use the sectional isolation method: disconnect the intermediate connector and measure the insulation of the front and rear harness sections separately to isolate the faulty wire segment.
  • 6
    Check the A/C controller side: Disconnect the controller connector and measure the corresponding pin-to-ground resistance to rule out an internal short circuit in the controller (very rare).
  • 7
    After repairing or replacing the faulty wiring harness/sensor, restore the connections and clear the fault code. Start the vehicle and turn on the air conditioning (set to 22°C, face mode). Run the system for 15 minutes and observe the 'front passenger face vent temperature' in the data stream to verify normal operation (the temperature should gradually decrease with airflow). Confirm the fault code does not return.
Real-World Cases
BYD DTC AI Analysis

2018 BYD Song MAX: Sensor Short Circuit from Water Ingress

✓
After heavy rain while parked outdoors, the passenger side A/C vents blew icy cold air and wouldn't adjust. The scanner showed active DTC B2A5A11. Sensor resistance measured 0.5Ω (shorted). Disassembly revealed the sensor mounted at the lowest point of the air duct. A blocked drain hole caused condensate to accumulate, completely submerging the connector and shorting the pins. Fix: Cleared the A/C drain tube, replaced the passenger face-level temperature sensor, dried the connector and applied anti-corrosion treatment. Fault cleared.
BYD DTC AI Analysis

2019 BYD Qin Pro DM Dashboard Wiring Harness Wear Case

✓
When driving on rough roads, the AC panel occasionally displayed an 'E3' error, eventually triggering DTC B2A5A11. Static sensor tests showed normal readings, but resistance to ground fluctuated when wiggling the harness. Removed the dashboard and found the harness retaining clip had fallen off where it passes through the metal bracket. Long-term rubbing against the sharp edge wore through 3 mm of insulation, exposing the copper core to the body. Repaired the wiring by soldering and adding heat-shrink tubing, re-secured the harness with a rubber grommet, and adjusted the routing to avoid interference.
BYD DTC AI Analysis

2019 Qin EV Sensor Aging Failure Case

✓
After 4 years, the passenger-side temperature display stuck at -40°C (ultra-low) with intermittent DTC B2A5A11. Sensor resistance measured only 50Ω at ambient temperature (normal: 2kΩ), indicating internal thermistor breakdown from aging. Harness insulation tested normal and connectors showed no water ingress. Replaced the OEM passenger-side face-level air temperature sensor (Part No.: EG-8107010B). Temperature display returned to normal; fault code cleared and has not returned.
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.