AU
B2A2013

BYD technical documentation defines DTC B2A2013 as "Evaporator Temperature Sensor Circuit Open," rather than a generic "cabin temperature sensor" fault — Seal U

Thermal Management System

BYD technical documentation defines DTC B2A2013 as "Evaporator Temperature Sensor Circuit Open," rather than a generic "cabin temperature sensor" fault.

Located inside the HVAC evaporator case, this sensor monitors the evaporator core surface temperature in real time.

It sends critical feedback to the air conditioning controller (AC ECU) to prevent evaporator icing, regulate compressor displacement, and control the electronic expansion valve opening.

The AC ECU logs an open circuit fault when it detects the sensor signal voltage remaining above 4.95V or below 0.05V (outside the valid range).

This fault triggers the A/C system protection logic, which forcibly disengages the compressor electromagnetic clutch or stops the electric compressor, completely disabling A/C cooling.

Because BYD New Energy Vehicles (NEVs) deeply integrate the A/C and battery thermal management systems (typically incorporating the battery chiller into the A/C refrigerant circuit), this fault can cascade into a battery cooling system failure.

This causes abnormal vehicle thermal management and may restrict power output.

The B2A2013 fault code on the Seal U indicates a high-severity open circuit fault in the evaporator temperature sensor inside the HVAC unit. This can disable A/C cooling and may affect battery thermal management. Common causes include a failed evaporator temperature sensor or damaged wiring near the firewall or instrument panel. The recommended fix is to visit an authorised BYD dealer for diagnosis and repair. Real case data is available, including typical repair cost information.
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Cases Logged
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Causes
Likely Causes — Seal U
  • 1Internal open circuit in the evaporator temperature sensor or thermistor characteristic drift, preventing the sensor from generating a valid temperature-resistance signal.
  • 2Sensor wiring harness worn, broken, or crushed at stress concentration points such as the firewall wiring grommet and instrument panel frame mounting points.
  • 3Oxidation, corrosion, or poor contact of the sensor connector plug pins due to evaporator condensate leakage, floor water ingress, or water intrusion during car washing.
  • 4Loose wiring harness retaining clip causes movement during driving. Prolonged strain breaks the wire at the connector base (intermittent open circuit).
  • 5Air conditioning controller internal signal sampling circuit fault (e.g., open voltage divider resistor or shorted filter capacitor), preventing correct identification of sensor signals.
What To Do
  • 1
    Use a dedicated diagnostic tool (such as VDS2000 or Launch X-431) to read the air conditioning system fault codes, confirm B2A2013 is present, and record the freeze frame data (abnormal ambient and evaporator temperature values are usually -40°C or a fixed high value).
  • 2
    Enter data stream mode and monitor the 'evaporator temperature sensor' value in real time. Turn on the air conditioning. If the value does not change or remains at an extreme value (-40°C/120°C), confirm the signal is abnormal.
  • 3
    Remove the front passenger glove box or lower dashboard trim panel. Locate the evaporator temperature sensor (usually a two-wire NTC thermistor on the evaporator housing). Visually inspect the connector for looseness, water ingress, or corrosion.
  • 4
    Disconnect the connector and measure the sensor resistance. At 25°C ambient temperature, the standard value is 1.8-2.5kΩ. Warm the sensor by hand; the resistance must decrease as the temperature rises (negative temperature coefficient characteristic). If the resistance is infinite or remains unchanged, replace the sensor.
  • 5
    Measure harness side voltage: With the ignition switch ON and the connector disconnected, measure the harness terminals for a 5V reference voltage (supplied by the AC ECU) and a ground circuit. If the voltage is 0V or 12V, check the power supply/ground wiring.
  • 6
    Measure harness continuity between the sensor and the AC ECU using a multimeter set to resistance. The standard resistance must be less than 1Ω. Specifically inspect the firewall wiring grommet and bends in the floor harness protective sleeve. Repair any open circuits and install a wear-resistant protective sleeve.
  • 7
    If the wiring harness and sensor are normal, measure continuity between the corresponding AC ECU pin and the sensor. If the ECU side does not output a 5V reference voltage, this indicates an internal A/C controller fault. Replace or repair the controller.
  • 8
    After repair, reconnect all connectors, clear the fault code, and run the 'Air Conditioning System Self-Diagnosis' or 'Component Test' function to confirm the evaporator temperature data stream returns to normal (typically 2-10°C, varying with operating conditions).
  • 9
    Perform a 30-minute road test to verify if the fault code returns. Check the A/C cooling performance and verify normal operation of the battery cooling system linkage.
Real-World Cases
BYD DTC AI Analysis

BYD Qin EV300 AC not cooling — oxidized connector causing intermittent open circuit

✓
2017 Qin EV300, 60,000 km. Owner reported the A/C suddenly stopped cooling, blowing ambient air. Scan tool showed DTC B2A2013 (evaporator temperature sensor circuit open) and B2A2111. Live data indicated evaporator temperature at -40°C (abnormal). Removed the glove box and found the evaporator temperature sensor connector loose with green oxidation on the pins. Measured sensor resistance at 2.1kΩ—normal—but the loose connection interrupted the signal. Cleaned the connector with electronic cleaner, polished the pins with fine sandpaper, applied conductive grease, and resecured the plug. Cleared the fault codes. Evaporator temperature now read 8°C, the compressor clutch engaged normally, and cooling was restored.
Original source ↗
BYD DTC AI Analysis

BYD Tang DM intermittent AC shutdown – sensor corroded by condensate

✓
A 2018 BYD Tang DM had intermittent AC cooling that suddenly cut out while driving, occasionally recovering after restart. DTC B2A2013 set intermittently. Live data showed evaporator temperature jumping between -40°C and actual values. Removing the evaporator housing revealed condensate pooling at the temperature sensor mounting hole; the sensor pins had corroded and blackened. Further inspection found the evaporator drain hole blocked with dust, causing condensate to accumulate and continuously soak the sensor. Cleared the drain hole, replaced the evaporator temperature sensor assembly, and applied waterproof sealant to the connector. Monitored for one month with no recurrence.
Original source ↗
BYD DTC AI Analysis

BYD Song Pro EV compressor not working — firewall wiring harness chafed through, open circuit

✓
A 2019 Song Pro EV had no cold air with the AC on; the compressor clutch did not engage. DTCs B2A2013 and B2A2A14 present. Evaporator temperature sensor supply measured 5V (normal), but the signal line measured 4.98V (close to reference voltage, indicating an open circuit). Traced the wiring and found the harness rubbing against a sharp metal edge at the firewall grommet; insulation was damaged and the wire broken. Cut out the damaged section, soldered the connection, insulated with heat-shrink tubing, rerouted the wiring, and added a rubber sleeve to prevent further chafing. Fault resolved.
Original source ↗
BYD DTC AI Analysis

Water in BYD Han EV floor corroded sensor connector

✓
A 2020 Han EV came in with the AC not cooling and the battery cooling system warning light on. The scan tool read DTC B2A2013 from the air conditioning system and a cooling system fault from the BMS. Inspection found water ingress at the wiring harness connector under the passenger floor; the evaporator temperature sensor connector pins had corroded and broken. Traced the source to a perished front windscreen seal letting rainwater into the floor. Replaced the corroded harness connector, dried the harness, repaired the seal, and raised the connector mounting position to keep it clear of standing water. Bled the battery cooling system and calibrated the AC.
Original source ↗
Other Seal U Fault Codes
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.B110A02DTC B110A02 indicates the thermal management master control unit (HVAC ECU) or body control module (BCM) failed to receive valid CAN data frames from the PM2.5 air quality sensor over consecutive communication cycles (typically 500ms per cycle). The sensor typically mounts at the HVAC unit air inlet or behind the glove box and transmits real-time particulate concentration data (unit: μg/m³) to the HVAC controller via the CAN bus. The fault is essentially a communication link layer timeout. Potential causes include physical layer wiring faults, sensor power supply failures, sensor internal MCU lockup, or CAN network topology damage. Although this non-critical fault does not directly affect driving safety, it disables the intelligent air purification strategy and the automatic fresh air/recirculation switching function. In extreme cases, it triggers a thermal management system degraded mode, limiting compressor power or fixing the air flap position.B110BDTC B110B indicates a fault in the internal air pump (sampling pump) of the PM2.5 air quality detector. This pump draws cabin or outside air into the PM2.5 sensor detection chamber, enabling the laser scattering sensor to measure real-time particulate matter concentration. The air conditioning controller (or BCM) sets this DTC upon detecting an open or short circuit in the pump drive circuit, or abnormal current caused by a seized pump motor. This fault disables the "Green Clean" system, causes the instrument cluster air quality display to read abnormally or disappear, and disables the automatic fresh air/recirculation switching function. It does not affect the vehicle powertrain or core thermal management functions.B173712DTC B173712 indicates a short to power in the firing circuit of the right second-row side airbag module in the Supplemental Restraint System (SRS). Specifically, the "right second-row side airbag" typically refers to the side impact airbag located in the right B-pillar or the side of the right seat. The "12" suffix indicates a circuit short to battery positive (B+). This fault causes the following conditions: 1) The airbag may fail to ignite and deploy during a collision, resulting in a loss of side impact protection. 2) In extreme cases, unintended triggering may cause accidental airbag deployment. 3) The SRS control unit detects abnormally high circuit voltage (typically above 4.5V) and enters fault protection mode. This may disable the entire airbag system and continuously illuminate the instrument cluster airbag warning light.
Common problems reported for Seal U →Seal U overview →
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.