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B2A5B11

This DTC indicates the Passenger Side Floor Vent Temperature Sensor signal circuit shorts to body ground (GND) — Atto 3

Thermal Management System

This DTC indicates the Passenger Side Floor Vent Temperature Sensor signal circuit shorts to body ground (GND).

In the BYD thermal management system, this sensor uses a negative temperature coefficient (NTC) thermistor.

During normal operation, it changes resistance between 2-10kΩ as the vent temperature changes, outputting a 0.5-4.5V analog voltage signal to the HVAC ECU.

A short to ground pulls the signal voltage near 0V.

The controller detects this abnormal signal, typically interpreting it as an excessively high temperature or a circuit fault.

This condition causes the following: 1) The passenger side floor vent closed-loop temperature control fails, potentially resulting in continuous maximum cooling or heating and affecting occupant comfort. 2) The air conditioning system enters fault protection mode and limits compressor speed.

In extreme cases, this affects the heat exchange efficiency of the battery pack thermal management circuit. 3) In extreme ambient temperatures, the incorrect temperature signal causes the thermal management system to miscalculate and trigger vehicle power limitation.

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Cases Logged
Real-World Cases
BYD DTC AI Analysis

Song MAX: Blocked evaporator drain caused sensor water ingress and short circuit

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Model: 2018 Song MAX DM, 32,000 km. Symptoms: After 10 minutes of A/C operation, the instrument cluster displayed "Thermal Management System Fault". The passenger footwell vent blew cold air continuously and would not adjust. Diagnosis: Scanned with VDS and retrieved DTC B2A5B11. Reviewed live data and found the passenger footwell temperature fixed at -40°C (abnormally low). Removed the passenger-side evaporator lower cover and found water inside the temperature sensor connector; the pins were oxidised and green. Further inspection showed dust had blocked the evaporator drain hose, letting condensate overflow onto the sensor mount. Fix: Cleared the drain hose, dried the connector with compressed air and sprayed electronic contact cleaner. Replaced the temperature sensor (pins too corroded to repair). After reassembly, live data returned to normal and temperature adjustment worked correctly.
BYD DTC AI Analysis

Qin Pro EV Wiring Harness Chafing Causes Short to Ground After Accident Repair

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Model: 2019 Qin Pro EV. Fault appeared after right front accident repairs. Symptoms: AC cannot auto-regulate temperature after repairs. VDS reports DTC B2A5B11. Diagnosis: Disconnected sensor; resistance measured normal (3.8kΩ@25℃). Harness-side signal line-to-ground resistance measured 0.3Ω, confirming short to ground. Traced passenger floor harness routing; found mounting bracket shifted during accident repairs. Harness rubbed against sharp body bracket edge, damaging insulation and allowing signal wire to contact body ground. Repair: Cut out damaged harness section (~15cm). Reconnected using waterproof crimp terminals. Wrapped with PVC tape and corrugated tubing. Rerouted harness to clear sharp edges. Fault cleared.
BYD DTC AI Analysis

Qin EV300 AC controller connector pins bent, poor contact

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Vehicle: 2017 Qin EV300, 85,000 km. Symptoms: With the AC in foot mode, the passenger footwell outlet was abnormally cold, and the 'motor overheating' warning light triggered falsely. Diagnosis: DTC B2A5B11. Sensor and harness resistance measured normal, but the fault appeared intermittently when wiggling the HVAC controller harness. Removed the lower centre console and inspected the HVAC controller connector (22-pin grey). Found pin 14 (temperature sensor signal, yellow wire) bent and contacting pin 13 (ground, black wire), causing a short. Repair: Used a specialised pin removal tool (M202) to straighten the bent pin. Checked the pin housing for cracks, applied conductive grease to ensure good contact, and reconnected and secured the harness. Fault resolved.
BYD DTC AI Analysis

Song MAX: Aftermarket floor mats pinched wiring harness, causing short circuit

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Model: 2019 Song MAX. Owner self-installed full-surround floor mats; fault appeared the next day. Symptoms: AC panel displayed "Check Air Conditioning System" and VDS reported DTC B2A5B11. Diagnosis: Sensor resistance read normal, but the signal wire at the sensor connector shorted to ground. The owner had secured the mats with metal clips that pierced the carpet and crushed the hidden AC temperature sensor harness underneath, damaging the signal wire insulation and causing a short to body. Solution: Removed the metal clips. Repaired the wiring by stripping the damaged insulation and applying heat-shrink tubing. Replaced them with plastic fixing clips. Rerouted the harness clear of the mat mounting area. Cleared the DTCs. System returned to normal.
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: Community This information is for reference only. Always consult a qualified technician for diagnosis and repair. Do not attempt high-voltage system repairs yourself.