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B2A1012

This DTC indicates a short to ground in the refrigerant temperature sensor signal circuit at the inlet or outlet of the battery cooling system plate heat exchanger (Chiller/battery cooler), or an internal short circuit within the sensor — Atto 3

Thermal Management System

This DTC indicates a short to ground in the refrigerant temperature sensor signal circuit at the inlet or outlet of the battery cooling system plate heat exchanger (Chiller/battery cooler), or an internal short circuit within the sensor.

This NTC thermistor outputs a 0.5-4.5 V analog voltage signal to the Thermal Management System (TMS) controller or A/C controller to monitor the temperature of the refrigerant flowing through the plate heat exchanger in real time.

This parameter is critical for precisely controlling battery cooling intensity and preventing battery overcooling or overheating.

The controller logs a short circuit fault when the signal voltage remains below 0.1 V (near 0 V) for a specified duration (typically 2-5 seconds).

The thermal management system then enters fail-safe mode, immediately cutting off refrigerant flow to the battery cooling circuit and limiting battery charge and discharge power.

In severe cases, the system triggers a vehicle-level 'Thermal Management System Fault' warning and prohibits high-voltage power-on.

This prevents continued operation with unknown refrigerant temperatures, which could cause battery thermal runaway or compressor liquid slugging damage.

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Cases Logged
Real-World Cases
BYD DTC AI Analysis

Underbody scrape wore through wiring harness causing intermittent short circuit

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2019 BYD Qin EV, 80,000 km. Owner reported intermittent "Thermal Management System Fault" warnings on the instrument cluster, particularly after driving on rough roads. Scanned DTCs B2A1012 (current) and B2A1012 (history). Raised the vehicle and inspected the plate heat exchanger wiring harness at the front of the battery pack. The retaining clip had detached and the harness rubbed the subframe edge, wearing through the insulation. Exposed copper contacted the frame, shorting to earth. Repair: Repaired the damaged harness (cut/reconnected or taped), re-secured the routing, added corrugated tubing protection, cleared DTCs. Monitored one week with no recurrence.
BYD DTC AI Analysis

Internal short in aging sensor caused battery cooling failure

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During routine maintenance, the shop detected active DTC B2A1012. No warning light illuminated on the dash, but live data showed refrigerant temperature at -40°C (abnormal). Disconnected the sensor and measured 0.2Ω resistance (near short circuit), diagnosing internal thermistor breakdown. The sensor sits inside the plate heat exchanger; replacing it separately risks refrigerant leakage. Solution: Recovered refrigerant, removed the old plate heat exchanger, installed a new plate heat exchanger assembly with integrated sensor, evacuated and recharged the refrigerant. Fault eliminated.
BYD DTC AI Analysis

Connector water ingress after wading caused corrosion and short circuit

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Owner reported the instrument cluster showed "Battery Cooling System Fault" after driving through 40 cm standing water. Found water stains and green corrosion inside the plate heat exchanger refrigerant temperature sensor connector. Measured 5 Ω between pin 2 (signal) and pin 1 (ground)—a short circuit. Cause: Deteriorated connector seal allowed water ingress under pressure during the crossing. Fix: Cleaned pins with electronic cleaner and compressed air, replaced the waterproof seal, applied insulating silicone grease to the harness connector, and cleared fault codes. Tested normal.
BYD DTC AI Analysis

False alarm from wiring harness installed incorrectly after accident repair

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Following front-end collision repairs, DTC B2A1012 triggered immediately at handover. Inspection found that during front compartment harness installation, technicians had incorrectly secured the plate heat exchanger temperature sensor harness beneath the AC pipe bracket. The metal bracket edge cut through the outer sheath, shorting the signal wire to ground. Repaired the damaged harness, rerouted it to clear the sharp bracket, and secured it with dedicated cable ties to the factory harness clips. Fault cleared. Post-collision repairs must verify harness routing complies with factory specifications.
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.