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 3

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.

4
Cases Logged
5
Causes
Likely Causes — Atto 3
  • 1The sunlight sensor wiring harness rubs against a sharp metal edge inside the dashboard, damaging the insulation. The signal wire contacts the constant power wire, causing a short circuit. This commonly occurs after driving on rough roads or after dashboard removal and installation.
  • 2During windscreen replacement or dash cam installation, the technician damaged the sun sensor wiring harness, pinching the signal and power wires 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 supply terminals. This typically occurs in high-temperature, high-humidity environments or after the vehicle drives through water.
  • 4Internal fault in the air conditioning controller (thermal management ECU) sampling circuit abnormally pulling the signal line up to supply voltage, or water ingress into the controller connector causing a short circuit between terminals.
  • 5After a minor collision in the front or passenger compartment, the wiring harness bracket deforms and shifts, causing the sunlight sensor wiring harness to interfere with and 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 sunlight 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. Locate the sunlight sensor below the windscreen (usually integrated into the same module as the automatic headlight sensor) and 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 is shorted, trace the sensor wiring harness to the air conditioning controller (located inside the dashboard or front compartment). Inspect the wiring harness for wear or damaged insulation, focusing on the dashboard frame routing hole and the 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 numbers usually have a BC-series prefix). 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 under both bright flashlight illumination and shaded conditions. Confirm the voltage changes normally within the 0.5V-4.5V range. Road test the vehicle to verify the automatic air conditioning sunload compensation function operates normally.
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

✓
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 3 Fault Codes
P0A0DBattery Energy Control Module Requested MIL IlluminationP0AA6Hybrid Battery Voltage System Isolation FaultP1A00Drive Motor "A" Performance — BYD proprietaryB1108For 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.
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.