AU
B2A0D13

DTC B2A0D13 indicates an open circuit in the Battery Pack Inlet Coolant Temperature Sensor — Seal U

Thermal Management System

DTC B2A0D13 indicates an open circuit in the Battery Pack Inlet Coolant Temperature Sensor.

This sensor is located at the inlet of the battery thermal management system cooling circuit.

Typically an NTC thermistor, the sensor provides a 0-5V analog voltage signal to the Battery Management System (BMS) or Thermal Management Controller (TMS) to monitor the temperature of the coolant entering the battery pack in real time.

An open circuit fault means the control unit detects that the signal voltage remains continuously in an open-circuit state (typically the 5V reference voltage or 0V, depending on circuit design), preventing it from obtaining actual temperature data.

This fault causes the thermal management system to enter fail-safe mode.

The system cannot accurately regulate the battery pack temperature, which may result in the following: (1) The system disables high-power charging and discharging, limiting vehicle power output. (2) The battery coolant pump and PTC heater fail to regulate to the target temperature, creating a risk of battery overheating or low-temperature damage. (3) In extreme cases, the system triggers the high-voltage interlock, preventing the vehicle from starting.

5
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Broken sensor wiring harness or loose connector: Long-term vibration, thermal cycling, or improper assembly breaks the internal copper strands of the wiring harness near the battery pack, or a failed connector locking tab causes poor contact.
  • 2Internal open circuit in the coolant temperature sensor: Aging, cracking, or detached solder joints of the internal thermistor element cause infinite resistance.
  • 3Connector terminal corrosion or backed-out pin: Coolant leakage or vehicle wading causes water ingress at the sensor connector, resulting in terminal oxidation, corrosion, or backed-out pins.
  • 4Hidden open circuit due to worn wiring harness insulation: Long-term chafing of the wiring harness against the battery pack housing edge, firewall pass-through, or underbody shield partially or completely breaks the internal wires.
  • 5Control unit internal sampling circuit fault: A damaged temperature sampling interface circuit in the BMS or thermal management controller prevents correct sensor signal identification.
What To Do
  • 1
    Connect the VDS2000/VDS1000 diagnostic tool, read the freeze frame data for DTC B2A0D13, and record the ambient temperature, battery temperature, and vehicle status when the fault occurred.
  • 2
    Visually inspect the coolant temperature sensor connector near the battery pack coolant inlet pipe for obvious looseness, signs of water ingress, corrosion, or wiring harness damage.
  • 3
    Disconnect the sensor connector and use a multimeter to measure the sensor resistance. The normal value should fall within the specified temperature range (e.g., approx. 2.5 kΩ at 25°C, approx. 7.5 kΩ at 0°C). If the multimeter displays infinity (OL), replace the sensor.
  • 4
    Measure the voltage on the wiring harness side: With the ignition switch in the ON position, the signal wire-to-ground voltage should be approximately the 5V reference voltage (or match the manufacturer's specified value), and the ground wire-to-ground resistance should be less than 1Ω. If the voltage is abnormal, check the wiring harness continuity.
  • 5
    Perform a wiring harness continuity test: Measure the continuity resistance of the signal and ground wires from the sensor connector to the BMS/TMS control unit. Resistance must be less than 1Ω. Closely inspect the wiring harness near the battery pack, firewall grommet, and chassis underbody shield.
  • 6
    Check the coolant level and lines: verify no coolant leaks have corroded the wiring harness. If necessary, repair the leak and replace the damaged wiring harness.
  • 7
    Repair or replace faulty components: install an OEM coolant temperature sensor (apply thermal grease), repair the broken wiring harness (use waterproof heat-shrink tubing), and ensure the connector locking tab fully engages.
  • 8
    Clear the fault code and verify functionality: read the data stream to confirm the inlet coolant temperature display is normal (deviation from actual temperature <2°C). Perform a fast charging or high-power discharge test to confirm the thermal management system operates normally.
Real-World Cases
BYD DTC AI Analysis

Qin EV restricted power while driving and displayed a battery overheating warning.

✓
After approximately 30 minutes of driving, the dashboard suddenly displayed "Powertrain Fault" and "Battery Overheating" warnings, and the vehicle automatically limited speed to 40 km/h. A VDS scan revealed DTC B2A0D13. Lifted the vehicle and found the coolant temperature sensor harness at the battery pack inlet had chafed against the edge of the underbody shield, causing internal conductor breakage while the insulation remained intact—a hidden open circuit. Repair: Cut out the damaged harness section, reconnected it with waterproof connectors, and rerouted the harness to avoid contact with the shield. Cleared the codes and test drove; live data showed the inlet coolant temperature returned to normal, with no abnormalities during high-power charging or discharging.
BYD DTC AI Analysis

Qin EV DC fast charging frequently cuts out

✓
While charging at a DC fast charging station, the vehicle repeatedly disconnected at around 60% SOC; the instrument cluster displayed a charging system fault. The scan tool retrieved DTC B2A0D13 and related thermal management fault codes. Found coolant crystallisation inside the battery pack inlet coolant temperature sensor connector (from a previous minor coolant leak), causing terminal corrosion and an open circuit. Replaced the battery pack inlet coolant temperature sensor (including seal), thoroughly cleaned the connector terminals, topped up coolant and bled the system. DC fast charging works normally after repair; fault codes have not returned.
BYD DTC AI Analysis

Tang DM LIN bus master node failure causing power window failure

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[Note: This case relates to LIN bus open-circuit fault characteristics, similar to the troubleshooting method for B2A0D13 open-circuit faults.] Customer reported all four door windows and the sunroof inoperative. The left front door switch would not control the other three doors, but each door's individual switch operated its own window. Diagnosis showed a LIN bus communication fault (B2A0D13 is also defined as a LIN open circuit in some documentation). The left front door control module (LIN master node) had normal power, but LIN line voltage was abnormal. Found the LIN bus wiring broken at the left front door hinge from repeated flexing. Repaired the harness; fault resolved.
Original source ↗
BYD DTC AI Analysis

Tang DM Sunshade Malfunction and LIN Communication Interruption

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Note: This case demonstrates a LIN network open-circuit fault for wiring troubleshooting reference. The left front door window switch backlight flickered; the switch failed to control the windows in the other three doors; the sunshade only closed halfway. The scan showed either no specific fault codes or a LIN communication fault. Measuring the LIN bus waveform revealed a signal interruption. Inspection of the left front door wiring harness connector found oxidised LIN bus pins with poor contact, causing a network open circuit. Cleaned and repaired the connector terminals; replaced the wiring harness plug where necessary. Fault resolved.
Original source ↗
BYD DTC AI Analysis

BYD Song TID intermittent no-start and body network fault

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Note: Reference for LIN/CAN bus open-circuit diagnosis. Intermittent no-start. Vehicle powers to ON but the starter does not crank. Instrument cluster displays warnings to check EPB and ESP systems. Scans found communication faults in multiple modules. Disconnecting LIN bus slave devices one by one (window lift modules, seat modules, etc.) identified an internal short in one LIN node pulling bus voltage low, creating open-circuit-like symptoms. Repaired the LIN bus wiring short/open circuit and replaced the faulty LIN slave device. System returned to normal.
Original source ↗
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.