AU
B2A5A11

This DTC indicates a short to ground in the signal circuit of the front passenger side FACE mode outlet air temperature sensor — Atto 8

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 — Atto 8
  • 1A breakdown and short circuit of the thermistor inside the temperature sensor body directly grounds the signal terminal.
  • 2Damaged wiring harness insulation inside the right dashboard A/C duct causes the signal wire to contact the metal duct or sharp body edges and short to ground.
  • 3Poor sensor connector sealing allows A/C condensate ingress, causing a short circuit between pins or a short to ground.
  • 4Detached wiring harness retaining clip causes prolonged harness chafing against the instrument panel frame during driving, resulting in damage.
  • 5Improper wiring harness routing after previous repairs caused the instrument panel trim to pinch the harness and pierce 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 outlet temperature sensor (usually located inside the right HVAC assembly 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 is internally shorted. Replace the sensor.
  • 3
    Keep the connector disconnected. Use a multimeter to measure the resistance between the harness-side signal pin (usually the yellow wire) and body ground. The normal value is greater than 10MΩ. If continuity exists, inspect the wiring harness along its routing for damage. Focus on sharp edges where the harness passes through the firewall and instrument panel bracket.
  • 4
    Inspect connector seal ring integrity. Check pins for oxidation, verdigris, or water marks. If necessary, clean with electronic contact cleaner and spray with WD-40 for waterproofing. Replace the connector if severely corroded.
  • 5
    If the wiring harness appears normal but is shorted 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 specific faulty wire section.
  • 6
    Check the A/C controller side: Disconnect the controller connector and measure the resistance from the corresponding pin to ground to confirm the controller has no internal short circuit (very rare).
  • 7
    After repairing or replacing the faulty wiring harness/sensor, restore connections and clear the fault code. Start the vehicle and turn on the A/C (set to 22°C, face mode). Run the system for 15 minutes, check the 'front passenger face vent temperature' in the data stream to verify normal operation (temperature should gradually decrease with airflow), and 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 Atto 8 Fault Codes
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.B110A02DTC B110A02 indicates the thermal management master control unit (HVAC ECU) or body control module (BCM) failed to receive valid CAN data frames from the PM2.5 air quality sensor over consecutive communication cycles (typically 500ms per cycle). The sensor typically mounts at the HVAC unit air inlet or behind the glove box and transmits real-time particulate concentration data (unit: μg/m³) to the HVAC controller via the CAN bus. The fault is essentially a communication link layer timeout. Potential causes include physical layer wiring faults, sensor power supply failures, sensor internal MCU lockup, or CAN network topology damage. Although this non-critical fault does not directly affect driving safety, it disables the intelligent air purification strategy and the automatic fresh air/recirculation switching function. In extreme cases, it triggers a thermal management system degraded mode, limiting compressor power or fixing the air flap position.B110B07This fault code indicates abnormal operation of the internal air pump (sampling pump) in the PM2.5 air quality detection module. The PM2.5 detector uses the laser scattering principle to measure particulate concentration and requires a built-in air pump to draw ambient air into the detection chamber at a constant flow rate. The ECU sets this code when it detects an open or short in the air pump drive circuit, abnormal current (stall or free-running), or abnormal speed feedback. This fault causes the automatic air conditioning system to lose air quality sensing capability, preventing automatic switching between fresh air and recirculation modes. The instrument cluster air quality display may show '--' or a fixed value, but the fault does not affect the vehicle powertrain or basic air conditioning cooling and heating functions.B173CDTC B173C indicates the Supplemental Restraint System (SRS) detects the Right Second Row Side Airbag squib circuit resistance exceeds the calibrated threshold (typically >4.5Ω). This fault is an active diagnostic result of the SRS system, indicating a high-resistance condition in the circuit between the Airbag Control Unit (ACU) and the airbag module. Causes for excessive resistance include increased contact resistance, a partially broken wiring harness, terminal oxidation, or an aging squib wire inside the airbag module. This fault causes the system to mark the airbag circuit as 'unreliable', meaning the airbag may fail to deploy during a collision. The fault typically illuminates the instrument cluster airbag warning light (SRS light) continuously, and some models also sound a warning buzzer.
Common problems reported for Atto 8 →Atto 8 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.