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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 — Seal U

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
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Causes
Likely Causes — Seal U
  • 1Damaged sensor wiring harness insulation causing a short to body ground (commonly caused by bottoming out, stone impacts, or prolonged chafing against sharp metal edges after a harness retaining clip loosens)
  • 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 causes a short circuit between the signal and ground pins (driving through water, improper high-pressure washing, seal aging)
  • 4Thermal management controller (TMS) or air conditioning controller internal signal sampling circuit short to ground (electrostatic breakdown or water ingress damage; relatively uncommon)
  • 5Incorrect wiring harness routing during repair causes metal bracket burrs to cut the insulation or the high-temperature exhaust pipe to melt the insulation, resulting in a short circuit.
What To Do
  • 1
    Use a BYD VDS2000 or Launch X431 to read all fault codes. Check for accompanying B2A0F (open circuit) or other thermal management fault codes. 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 end of the chassis battery pack, connecting the electric compressor outlet pipe and the battery cooling pipe) for damage, crushing, or signs of water ingress. Focus on the contact points between the wiring harness and the body metal brackets.
  • 3
    Disconnect the sensor connector (typically a 2-pin black waterproof connector on the side of the plate heat exchanger housing). Measure the resistance between the two terminals on the sensor body using a multimeter. At a 25°C ambient temperature, the normal value is approximately 10kΩ±5%. If the resistance approaches 0Ω or infinity, the sensor has an internal short or open circuit.
  • 4
    Keep the connector disconnected and turn the key to the ON position. Measure the voltage between the harness-side signal pin (usually the 5V reference voltage) and ground. The normal reading is approximately 5V. If the reading is 0V, check the 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 resistance must be greater than 10 MΩ. If the resistance is too low, inspect the wiring harness in sections, focusing on wear points at the firewall pass-through and the inside of the underbody shield.
  • 6
    If testing confirms an internal sensor short circuit, recover the refrigerant (R134a or R1234yf), remove the plate heat exchanger end cover or lines, and replace the refrigerant temperature sensor (on some models, replace the entire plate heat exchanger assembly).
  • 7
    Repair the damaged section of the wiring harness (apply double-layer insulation using heat-shrink tubing or waterproof tape). Maintain a clearance of at least 20 mm 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 the specified amount of refrigerant oil and refrigerant. Use the diagnostic tool to clear the fault code. 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 Seal U Fault Codes
B1108For 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.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.B110913DTC B110913 indicates an open signal circuit for the PM2.5 rapid detector (in-cabin air quality sensor). This sensor typically mounts inside the air conditioning system intake duct. It monitors in-cabin PM2.5 concentration in real time and provides data to the automatic air conditioning system for intelligent control of the air purification function. The BYD diagnostic protocol uses sub-code '13' to specifically indicate an open signal circuit. Although this fault theoretically affects a comfort feature, BYD Qin series vehicles classify it as a Level 3 (severe) fault. This classification occurs because the air conditioning system interacts with the battery thermal management system (e.g., monitoring battery cooling intake air quality). The fault can disable the automatic air conditioning mode and prevent the air purification function from operating. In extreme cases, it affects the battery compartment intake air quality assessment, triggering the 'repair immediately' strategy.B110AThis DTC indicates interrupted CAN bus communication or abnormal data between the air conditioning control unit (ACU) and the PM2.5 air quality sensor. The PM2.5 sensor monitors particulate concentration inside and outside the vehicle and provides the basis for purification control in the automatic air conditioning system. The ACU triggers this fault if it fails to receive a valid CAN message from the sensor within the specified period (usually 100-500 ms), if message verification fails, or if the signal frame times out. Although this fault does not affect vehicle driving safety, it disables the automatic air purification function. The air conditioning system cannot automatically switch between recirculation and fresh air modes or activate the air purification mode based on air quality. A persistent fault may restrict the thermal management strategy.
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.