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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.

4
Cases Logged
5
Causes
Likely Causes — Atto 3
  • 1Damaged sensor wiring harness insulation causing a short to body ground (commonly due to underbody impacts, stone strikes, or prolonged chafing against sharp metal edges after a harness retaining clip detaches).
  • 2Internal NTC thermistor breakdown or circuit board short circuit in the plate heat exchanger refrigerant temperature sensor (aging, overheating, or manufacturing defects)
  • 3Water ingress and corrosion in the connector causing a short circuit between the signal pin and ground pin (driving through water, improper high-pressure washing, aging sealing ring)
  • 4Short circuit to ground in the internal signal sampling circuit of the thermal management controller (TMS) or air conditioning controller (electrostatic breakdown or water ingress; relatively rare)
  • 5Incorrect wiring harness routing during repair results in a short circuit when metal bracket burrs cut the insulation or the high-temperature exhaust pipe melts the insulation.
What To Do
  • 1
    Use a BYD VDS2000 or Launch X431 to read all fault codes. Check for an accompanying B2A0F (open circuit) or other thermal management fault codes, and record any abnormal temperature values in the freeze frame data.
  • 2
    Visually inspect the wiring harness at the plate heat exchanger (located in the front compartment or at the front of the chassis battery pack, connecting the electric compressor outlet pipe to the battery cooling pipe) for damage, crushing, or signs of water ingress. Closely inspect the contact points between the wiring harness and the body metal brackets.
  • 3
    Disconnect the sensor connector (usually a 2-pin black waterproof plug located on the side of the plate heat exchanger housing). Use a multimeter to measure the resistance between the two terminals of the sensor body. At 25°C, the normal value is approximately 10kΩ±5%. A resistance near 0Ω or infinity indicates an internal short or open circuit in the sensor.
  • 4
    Keep the connector disconnected. Turn the key to the ON position. Measure the voltage between the harness-side signal pin (usually the 5V reference voltage) and ground. Normal voltage is approximately 5V. If the reading is 0V, check the wiring harness for a short to ground or an internal ECU fault.
  • 5
    Use a megohmmeter to measure the insulation resistance between the signal wire and body ground. The value must be greater than 10MΩ. If the resistance is too low, inspect the wiring harness in sections. Focus on harness wear points at the firewall pass-through and inside the underbody shield.
  • 6
    If diagnostics confirm an internal short circuit in the sensor, recover the refrigerant (R134a or R1234yf), remove the plate heat exchanger end cover or lines, and replace the refrigerant temperature sensor (some models require replacing the complete plate heat exchanger assembly).
  • 7
    Repair the damaged section of the wiring harness (use heat-shrink tubing or waterproof tape for double-layer insulation). Maintain a minimum 20 mm clearance between the wiring harness and metal components. Apply conductive grease and reconnect the connector.
  • 8
    Evacuate the system to -95 kPa and hold for 15 minutes to confirm no leaks, then refill with the specified amount of refrigerant oil and refrigerant. Clear the fault code using the diagnostic tool. Perform a thermal management system self-test and a road test to verify the battery cooling function.
Real-World Cases
BYD DTC AI Analysis

Underbody scrape wore through wiring harness causing intermittent short circuit

✓
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

✓
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

✓
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

✓
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: Official This information is for reference only. Always consult a qualified technician for diagnosis and repair. Do not attempt high-voltage system repairs yourself.