AU
B2A2712

This DTC indicates the signal circuit of the automatic air conditioning system’s sun sensor (solar intensity sensor) has shorted to the vehicle power supply (B+, usually a constant 12V supply) — Atto 8

Thermal Management System

This DTC indicates the signal circuit of the automatic air conditioning system’s sun sensor (solar intensity sensor) has shorted to the vehicle power supply (B+, usually a constant 12V supply).

The sun sensor generally uses a photodiode or photoresistor.

During normal operation, the sensor outputs an analog voltage signal of 0.1-4.9V to the air conditioning controller (integrated into the thermal management module).

The signal voltage increases as sunlight intensity increases.

When the signal wire shorts to power, the controller detects the voltage remains continuously above 4.9V (close to battery voltage, 12-14V) and logs a short-to-power fault.

This fault disables the automatic air conditioning system's solar compensation function.

The air conditioning controller cannot automatically adjust outlet air temperature and blower speed based on sunlight intensity.

In extreme cases, the short-circuit current may burn out the air conditioning controller's internal sampling circuit.

Consequently, the system reports a severe fault and may enter protection mode.

The B2A2712 fault code on the Atto 8 indicates a high-severity short to power in the automatic air conditioning sun sensor signal circuit. The controller sees voltage above the normal 0.1–4.9V range, disabling solar compensation and possibly triggering protection mode. Common causes include dashboard wiring chafing or harness damage during windshield or dash cam work. Visit an authorised dealer for diagnosis and repair. Typical repair cost data is available from recorded cases.
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Cases Logged
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Causes
Likely Causes — Atto 8
  • 1The sunlight sensor wiring harness chafes against a sharp metal edge inside the dashboard, wearing through the insulation and shorting the signal wire to the constant power wire. This commonly occurs after driving on rough roads or after dashboard removal and installation.
  • 2During front windshield replacement or dash cam installation, the technician accidentally damaged the sun sensor wiring harness, crushing the signal wire and power wire together and causing a short circuit.
  • 3Internal photoelectric element breakdown or seal failure in the sun sensor causes an internal short circuit between the signal and power terminals. This typically occurs in high-temperature, high-humidity environments or after driving through water.
  • 4Internal sampling circuit fault in the air conditioning controller (thermal management ECU) abnormally pulling the signal line up to supply voltage, or water ingress into the controller connector causing a short circuit between terminals.
  • 5A minor collision in the front or passenger compartment deforms and displaces the wiring harness bracket, causing the sun sensor wiring harness to chafe against constant power circuits such as the cigarette lighter and reading lamp.
What To Do
  • 1
    Use the VDS2100 diagnostic tool to read the DTC freeze frame, confirm the sun sensor voltage when the fault occurred (usually reading above 5.0V or 12V), and observe if the current data stream remains abnormal.
  • 2
    Remove the upper dashboard trim panel and locate the sunlight sensor below the windscreen (usually integrated into the same module as the automatic headlight sensor). Disconnect the sensor connector.
  • 3
    Measure the voltage between the sensor connector signal pin (usually pin 2) and ground: if the voltage remains 12V, the wiring harness has a short circuit; if the voltage is 0V, the sensor has an internal short circuit.
  • 4
    If the wiring harness has a short circuit, trace the sensor wiring harness to the air conditioning controller (located inside the dashboard or front compartment). Inspect the harness for wear or damaged insulation, focusing on the dashboard frame routing hole and firewall grommet. Repair and re-wrap the damaged wiring harness.
  • 5
    If the sensor has an internal short circuit, replace the sunload sensor assembly (part number prefix is usually BC series). After replacement, use a diagnostic tool to perform A/C system self-learning or sensor calibration (required on some models).
  • 6
    Clear the fault code. Read the data stream while illuminating the sensor with a high-intensity flashlight, then while covering it. Confirm the voltage changes normally within the 0.5V-4.5V range. Road test the vehicle to verify the automatic air conditioning solar compensation function is restored.
Real-World Cases
BYD DTC AI Analysis

Song MAX aftermarket dashboard modification caused wiring harness chafing and short circuit

✓
A 2018 Song MAX DM lost air conditioning cooling and set code B2A2712 after a head-up display (HUD) installation. Technicians found the aftermarket shop had failed to reposition the sunlight sensor harness when removing the dashboard, trapping it against the frame. While driving, the harness chafed against the metal edge, wearing through the insulation and shorting the signal wire to constant power. Repair: Re-routed the harness, wrapped it in abrasion-resistant corrugated tubing, and replaced the damaged sunlight sensor connector. Fault resolved.
BYD DTC AI Analysis

Sensor inoperative after front windscreen replacement on Qin Pro EV

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2019 BYD Qin Pro EV: One week after the dealership replaced the front windscreen, the instrument cluster displayed 'Thermal Management System Fault' and stored DTC B2A2712. Technicians found the sunlight sensor harness pinched between the windscreen and dashboard from the glass installation, breaking internal copper conductors and shorting them to the power wire. The diagnostic scanner showed sensor voltage locked at 13.2V (battery voltage). Repaired the damaged harness, adjusted the routing to prevent further pinching, cleared the fault codes, and the system returned to normal.
BYD DTC AI Analysis

Water entered the sensor connector and caused a short circuit after driving through deep water.

✓
A 2017 Qin EV300 developed automatic air conditioning fan speed control failure after driving through water during heavy rain. Diagnosis found abnormally high signal voltage from the sunlight sensor. Removing the sensor revealed water staining and corrosion inside the connector. The sensor mounts below the windscreen; a blocked drain channel allowed water to backflow into the connector. Technicians cleaned and dried the sensor connector, cleared the front windscreen drain channel, and applied insulating silicone grease to the connector to prevent future water ingress. Fault resolved.
BYD DTC AI Analysis

Song MAX Thermal Management Controller Internal Fault Misdiagnosis

✓
2019 Song MAX repeatedly throwing DTC B2A2712. Replaced the sunload sensor and wiring harness; fault persisted. Deep inspection found a burnt pull-up resistor in the air conditioning controller (integrated thermal management module) internal signal sampling circuit, forcing the sensor signal line to 12V. Controller internal short-circuit current back-fed into the sensor circuit, causing the fault. Replaced the AC controller assembly (PN 6A-8112010), continuity-tested the wiring harness to confirm no short-circuit risks, and delivered the vehicle.
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.