AU
B2ABB-17

This fault code indicates the voltage on the high-voltage side of the electric air conditioning compressor exceeds the controller's safety threshold (typically 750V-800V DC, depending on the vehicle's high-voltage platform) — Seal U

Thermal Management System

This fault code indicates the voltage on the high-voltage side of the electric air conditioning compressor exceeds the controller's safety threshold (typically 750V-800V DC, depending on the vehicle's high-voltage platform).

The system triggers the high-voltage interlock protection mechanism to prevent overvoltage breakdown of the compressor's internal power semiconductors (IGBT or SiC modules).

When the BMS or compressor controller detects the bus voltage momentarily or continuously exceeds the calibrated upper limit, it logs this fault and limits or disables compressor operation.

This causes a loss of air conditioning cooling and heating functions and, in extreme cases, triggers reduced-power operation of the vehicle's high-voltage system.

The B2ABB-17 fault code on the Seal U indicates the electric air conditioning compressor is seeing high-voltage input above its safe limit. This is a medium-severity fault that can disable cooling or heating and may limit high-voltage system operation. Common causes include voltage spikes during DC fast charging or heavy regenerative braking, or a faulty compressor voltage sensing circuit. Visit an authorised dealer for diagnosis and repair. Typical repair cost data is available.
5
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Traction battery pack voltage spikes momentarily during the final stage of DC fast charging or heavy regenerative braking, exceeding the compressor controller's upper tolerance limit.
  • 2Fault in the internal voltage sampling circuit of the air conditioning compressor high-voltage controller (ACCM), such as voltage divider resistor drift or Hall sensor miscalibration causing a false code.
  • 3Main positive/main negative contactor in the high-voltage power distribution unit (PDU) welded or stuck, causing uneven voltage distribution and generating voltage spikes.
  • 4Loose or burnt compressor high-voltage wiring harness connector (usually located near the right longitudinal rail in the front compartment) causes excessive contact resistance and triggers a transient overvoltage.
  • 5Outdated vehicle software version, overly sensitive voltage threshold calibration, or unsynchronized detection caused by BMS communication delay.
What To Do
  • 1
    Use the BYD dedicated diagnostic tool (ED-400/ED-500) to read the detailed fault data stream. Record the bus voltage, SOC status, and ambient temperature at the time of the fault to distinguish between a true overvoltage condition and a false sampling report.
  • 2
    Check the consistency of the traction battery pack total voltage and cell voltages. Use the diagnostic tool to perform a BMS active balancing test to rule out falsely high total voltage caused by cell overcharging.
  • 3
    Disconnect the Manual Service Disconnect (MSD). Wait 5 minutes, then inspect the air conditioning compressor high-voltage wiring harness connector (typically orange, located on the right side of the front compartment) for burn marks, water ingress, or looseness. Measure the insulation resistance between the terminals (should be >500MΩ).
  • 4
    Power on again. Turn on the air conditioning. Use a multimeter to measure the actual voltage at the compressor high-voltage input terminal and compare it to the diagnostic tool reading. If the deviation exceeds ±5%, replace the compressor controller.
  • 5
    Check the contactor status inside the high-voltage power distribution unit (PDU). Measure the voltage drop across the contactor. If the voltage drop is >50mV in the closed state, replace the contactor assembly.
  • 6
    If hardware inspection reveals no faults, update the air conditioning controller (ACCM) and BMS to the latest software versions, then recalibrate the high-voltage side voltage threshold.
  • 7
    Clear the fault code. Perform a DC fast charging and full-load air conditioning test (minimum 30 minutes recommended) to verify the fault does not recur.
Real-World Cases
BYD DTC AI Analysis

AC Compressor Not Working After Fast Charging: Case Report

✓
A 2018 Qin PRO DM fast-charged to 95% at a DC charging station. Turning on the air conditioning triggered DTC B2ABB-17 and the AC stopped cooling. Diagnosis found the fault occurred the instant fast charging ended: battery pack voltage hit 712V (nominal 653V), exceeding the compressor controller's 750V protection threshold. Inspection found the BMS charging cut-off voltage calibration was off. Updated BMS software to V2.3, correcting the charging cut-off voltage to 705V. Fault resolved.
BYD DTC AI Analysis

Poor contact in the high-voltage harness caused transient overvoltage

✓
While driving, the air conditioning on a 2019 Qin Pro EV suddenly cut out and the dashboard displayed a thermal management fault. Data logs showed the bus voltage spiked to 820V when the fault occurred (actual battery voltage was only 620V). Inspection found the internal spring clip in the compressor high-voltage connector had loosened, increasing contact resistance and generating an induced voltage spike under the compressor's start-up current surge. Replaced the high-voltage harness and applied conductive paste. Monitored for two weeks with no recurrence.
BYD DTC AI Analysis

Compressor controller sampling circuit fault

✓
2017 BYD Qin EV300 repeatedly threw DTC B2ABB-17. Bus voltage measured only 640V—well below the 750V threshold. Disassembled the compressor controller: the internal voltage sampling divider resistors (100kΩ/1% tolerance) had drifted to 107kΩ from prolonged heat exposure, causing the controller to falsely flag overvoltage. Replaced the electric compressor assembly (integrated controller and compressor). Fault resolved. Advised owner to avoid prolonged fast charging in extreme heat.
BYD DTC AI Analysis

Software mismatch after high voltage distribution box replacement

✓
After collision repairs, a Qin PRO DM had its high-voltage distribution box (PDU) replaced. The vehicle then set intermittent fault code B2ABB-17. Diagnosis revealed an approximately 200ms delay between the new PDU's contactor closure timing and the ACCM voltage sampling sequence, causing the sampling to capture voltage spikes from contactor bounce. Reflashing the ACCM software and adjusting the voltage sampling filter time constant from 10ms to 50ms completely resolved the fault.
BYD DTC AI Analysis

False positive fault in low temperature conditions

✓
Northern winter case: Qin EV300 set DTC B2ABB-17 on cold start at -15°C; cleared after 10 min driving. Data stream analysis showed increased battery internal resistance in the cold. ACCM sampling circuit captured overshoot voltage during voltage-drop recovery as the AC engaged. Software calibration boundary case. Fix: ACCM software update adding low-temperature compensation (voltage threshold raised 20V when ambient temp <-10°C).
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.