AU
B2AB64B

DTC B2AB64B indicates the electric A/C compressor internal temperature monitoring point detects an abnormally high temperature or an abnormal temperature signal — Seal U

Thermal Management System

DTC B2AB64B indicates the electric A/C compressor internal temperature monitoring point detects an abnormally high temperature or an abnormal temperature signal.

On 2019 BYD Qin EV models, this fault typically indicates the electric scroll compressor (BYD in-house or third-party supplied) internal motor winding temperature, power module (IPM) temperature, or compressor housing temperature exceeds the normal operating range (typical threshold: 110–130°C).

When this fault occurs, the compressor controller enters protection mode.

It limits compressor speed or stops operation to prevent insulation damage or mechanical seizure.

Because the Qin EV uses the A/C system for battery thermal management (the battery chiller integrates into the A/C circuit), this fault causes loss of cabin cooling and can reduce traction battery cooling capacity, subsequently triggering battery thermal management power derating protection.

The B2AB64B fault code on the Seal U indicates the electric A/C compressor is detecting an abnormally high internal temperature or an invalid temperature signal. Severity is medium because compressor protection can reduce or stop cooling, affecting cabin comfort and battery thermal management. Common causes include low or contaminated refrigerant flow, or a faulty compressor temperature sensor or wiring. The recommended fix is to visit an authorised dealer for diagnosis and repair. Typical repair cost data is available.
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Cases Logged
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Causes
Likely Causes — Seal U
  • 1Abnormal refrigerant circulation: A system refrigerant leak causes insufficient flow, or air/moisture in the refrigerant degrades compressor cooling and lubrication, causing frictional heating of the compressor pump body.
  • 2Compressor temperature sensor fault: NTC thermistor open circuit, short circuit, or resistance drift; water ingress or poor connection at the sensor wiring harness connector, causing a false high-temperature reading.
  • 3Compressor assembly mechanical fault: scroll plate wear, bearing seizure due to lack of lubrication, or degraded motor insulation increases running resistance and copper loss, generating abnormal heat.
  • 4Poor cooling system efficiency: A dirty or blocked condenser, insufficient cooling fan speed, or a blocked cooling air duct causes excessive high-side pressure and increases compressor load.
  • 5Electronic control system fault: Abnormal compressor controller (inverter) internal IPM module drive, current sampling resistor failure, or improper software over-temperature protection threshold setting.
What To Do
  • 1
    Use VDS2000 or the BYD dedicated diagnostic tool to read the freeze frame data. Record the compressor speed, high-side pressure, internal temperature, and ambient temperature at the time of the fault to determine whether it is actual overheating or a false sensor reading.
  • 2
    Check the air conditioning system refrigerant quantity and purity. Use a refrigerant recovery machine to extract and weigh the refrigerant to check for low charge (standard quantity approximately 600-700g, depending on configuration). If necessary, perform a pressure-holding leak test (hold pressure at 1.5MPa, 30-minute pressure drop <0.1MPa).
  • 3
    Measure the compressor temperature sensor resistance (approximately 10 kΩ at 25°C; resistance decreases as temperature increases). Check the sensor wiring harness for continuity and shorts to ground or power. Inspect connector pins B12/B13 and others for push-out or corrosion.
  • 4
    Check compressor operation: Disconnect the high-voltage service disconnect. Measure the compressor three-phase winding resistance (normal value 0.5–2 Ω, three-phase balance <5%). Measure the insulation resistance to the housing (>20 MΩ). Power on and check for abnormally high compressor operating current (normal: 6–8 A; faulty: >15 A).
  • 5
    Check the thermal management system heat dissipation capacity: clean debris from the condenser surface, check the electric fan high- and low-speed operation and duty cycle control, and verify the cooling fan controller (RFC) operates normally. If necessary, replace the receiver drier, then evacuate and recharge with the standard amount of refrigerant.
  • 6
    If the above checks are normal but the fault occurs intermittently, replace the compressor assembly (with controller) and confirm the software version (some early vehicles require updating the compressor controller software to the latest version to optimise the overtemperature protection strategy).
Real-World Cases
BYD DTC AI Analysis

Minor refrigerant leak triggered compressor thermal protection.

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2019 Qin EV, 80,000 km. After 30 minutes of summer highway driving, the air conditioning suddenly stopped cooling. No warning lights on the dash, but DTC B2AB64B logged. Freeze frame showed compressor internal temperature at 128°C (threshold 125°C) and high-side pressure at 2.8 MPa (elevated). Inspection found oil residue at the lower left corner of the condenser; a pressure test revealed a minor leak. Recovered only 450g of refrigerant (standard 650g). Replaced the condenser and seals, recharged the refrigerant, and ran continuous high-speed testing for 2 hours. Compressor internal temperature stabilized at 85-95°C. Fault resolved.
BYD DTC AI Analysis

Loose connection in compressor temperature sensor wiring harness causing false alarms

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Vehicle intermittently logged DTC B2AB64B approximately once per week, clearing after restart. Diagnostic tool showed internal temperature of -40°C when fault occurred (sensor open-circuit value). Checked compressor controller connector B12: pin 3 (temperature signal) had loose retention and detached when lightly pulled. Repaired pin, applied conductive grease, and re-secured harness routing to prevent vibration interference. No recurrence after 3 months.
BYD DTC AI Analysis

Seized compressor bearing caused high temperature

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At 60,000 km, the vehicle emitted a sharp screech after turning on the air conditioning, then set DTC B2AB64B and shut down the AC. Tore down the compressor: the scroll bearing was grinding dry from oil starvation; increased rotor axial clearance caused rotor-to-stator rubbing, overheating and discoloring the windings locally. Three-phase winding resistance measured 1.2Ω/1.3Ω/0.8Ω (imbalanced) with insulation resistance down to only 2MΩ. Replaced the electric compressor assembly, flushed the AC lines—found substantial metal debris—and replaced the receiver drier and expansion valve. Fault cleared completely.
BYD DTC AI Analysis

High ambient temperature and high battery cooling load caused overheating

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40°C summer ambient. During fast charging with battery cooling active, the compressor ran continuously at 6000rpm and set DTC B2AB64B. Insufficient condenser cooling combined with high ambient temperature caused the fault. The cooling fan ran at high speed, but condenser fins were severely clogged with catkins. After deep-cleaning the condenser, compressor internal temperature dropped from 122°C to 105°C under identical conditions; protection did not trigger again. Advised owner to clean the condenser regularly, particularly during pollen and catkin season.
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.