AU
B2A5A13

This DTC indicates an open circuit fault in the front passenger side face vent (face mode) temperature sensor circuit — Atto 8

Thermal Management System

This DTC indicates an open circuit fault in the front passenger side face vent (face mode) temperature sensor circuit.

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

Its resistance decreases as temperature rises.

If an open circuit occurs in the sensor body, wiring harness, or connector, the air conditioning controller (AC ECU) detects a continuous high signal voltage (typically near the 5V reference voltage).

This exceeds the normal operating voltage range (0.5V-4.5V), prompting the AC ECU to log an open circuit fault.

This fault forces the front passenger side temperature control into fail-safe mode.

The air conditioning system cannot accurately regulate the front passenger side outlet air temperature.

Symptoms may include one side blowing cold while the other blows hot, the compressor running continuously at high frequency or failing to start, and dual-zone synchronization failure.

A prolonged fault may reduce air conditioning system efficiency and increase high-voltage battery power consumption.

4
Cases Logged
5
Causes
Likely Causes — Atto 8
  • 1Internal open circuit in the sensor body: Aged and fractured NTC thermistor or pin dry solder joint, resulting in infinite resistance.
  • 2Wiring harness break or wear: The copper core of the passenger-side dashboard internal wiring harness fractures under frequent temperature changes or vibration stress, leaving the insulation visually intact (hidden break).
  • 3Poor connector contact: G86 connector (usually located near the front passenger-side air duct) has backed-out pins, oxidation, corrosion, or a loose locking tab, causing an intermittent connection.
  • 4ECU terminal fault: Corresponding pin of the air conditioning controller connector is loose or oxidized, or internal circuit board solder joints are cracked.
  • 5Modification or repair damage: Wiring harness crushed, cut, or severed during previous dashboard removal and installation, cabin air filter replacement, or dash cam installation.
What To Do
  • 1
    Diagnostic tool verification: Use the VDS2000/BYD dedicated diagnostic tool to read the live data stream. Confirm the front passenger face vent temperature sensor displays -40°C or 255°C (depending on calibration logic) and differs significantly from other air outlet temperature sensors.
  • 2
    Physical location check: Remove the passenger-side lower dashboard trim panel and locate the temperature sensor mounting position (usually at the face-level air duct outlet). Visually inspect sensor connector G86 for looseness, backed-out pins, or signs of water ingress.
  • 3
    Circuit continuity test: Disconnect the air conditioning controller and sensor connectors. Use a multimeter to measure the resistance between the signal wire (typically pin G86-1 to AC ECU B05-XX) and the ground wire (G86-2). Normal resistance is less than 1Ω. An open circuit displays OL or infinity.
  • 4
    Sensor unit test: Remove the sensor and measure its resistance at 25°C. The resistance must be 1.5-2.5 kΩ (refer to the workshop manual for the specific calibration value). If the circuit is open, replace the sensor (part numbers usually begin with HAC or HVAC).
  • 5
    Repair the wiring harness: If the harness is broken, repair it using waterproof connectors or solder and heat-shrink tubing. Check stress concentration points such as the instrument panel frame edge and harness retaining clips.
  • 6
    Verify repair: Restore all connections, clear fault codes, and start the air conditioning system. Monitor the data stream to confirm the sensor temperature value responds normally to outlet air temperature changes (the variation range should synchronize with other sensors).
Real-World Cases
BYD DTC AI Analysis

Internal break in Song MAX dashboard air duct temperature sensor wiring harness

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Vehicle: 2018 Song MAX DM, 62,000 km. Fault: Passenger side AC blowing cold air continuously, temperature would not adjust, instrument panel reported AC system fault. Diagnosis: VDS retrieved DTC B2A5A13, live data showed passenger face-level vent temperature sensor at -40°C (abnormal). Removed passenger glovebox and inspected sensor connector G86 on the air duct; appearance normal. Sensor resistance measured open circuit, though sensor body showed no damage. Traced wiring harness and found at the dashboard metal bracket edge: insulation intact, but internal copper cores completely fractured from long-term vibration and chafing. Solution: Replaced temperature sensor assembly (including wiring section), rerouted harness to avoid contact with sharp metal edges, fault cleared.
BYD DTC AI Analysis

Qin Pro EV passenger air vent sensor pin oxidation

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Vehicle: 2019 Qin Pro EV, 3 years in a coastal region. Symptoms: Intermittent AC operation; fault frequency increases in rain or high humidity. Diagnosis: Stored DTC B2A5A13 (intermittent). Sensor connector G86, pin 2 (ground) showed green corrosion and loose contact. Resistance fluctuated between 0.5Ω and open circuit when wiggling the harness. Repair: Cleaned pins with electrical contact cleaner, adjusted socket spring clips to increase contact pressure, applied conductive protective grease, and reassembled. No recurrence after one month.
BYD DTC AI Analysis

Qin EV open circuit alarm from reversed wiring harness connector after air conditioning repair

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Vehicle: 2017 BYD Qin EV300, accident repair. Symptom: After the dealership replaced the front bumper and condenser, the passenger side had no heat. Diagnosis: Retrieved DTC B2A5A13. Inspection found the technician had cross-connected the passenger face-level temperature sensor plug G86 with the recirculation door actuator plug during the collision repair. Although the connectors differed in shape, the technician forced the wrong plug onto the sensor, leaving the terminals unconnected and causing an open circuit. Resolution: Verified connector positions against the wiring diagram, confirmed the G86 plug matched the sensor, cleared the fault codes. System returned to normal.
BYD DTC AI Analysis

Song Max sensor body thermistor aged and fractured

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Vehicle: 2017 Song MAX, 85,000 km, long-term use in high-temperature regions. Symptom: Passenger-side AC suddenly failed during summer heat, reporting a thermal management fault. Diagnosis: Retrieved DTC B2A5A13. Sensor wiring continuity tested normal with 5V reference at the plug. Removed the sensor and found the NTC thermistor's internal ceramic body had micro-cracks from long-term thermal cycling stress. It tested intermittent at room temperature but fully open when hot. Sensor resistance measured infinite. Fix: Replaced the passenger side face-level outlet temperature sensor (part number: HAC-8112420), calibrated the air conditioning system temperature learning values. Fault cleared.
Other Atto 8 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.