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B2AB8-1C

DTC B2AB8-1C (abbreviated from B2AB81C) indicates the Electric A/C Compressor controller detected an abnormally high three-phase drive voltage — Qin Plus

Thermal Management System

DTC B2AB8-1C (abbreviated from B2AB81C) indicates the Electric A/C Compressor controller detected an abnormally high three-phase drive voltage.

This fault involves the Intelligent Power Module (IPM) or IGBT drive circuit inside the compressor controller (Inverter).

The controller triggers this fault upon detecting any of the following conditions: 1) Inter-turn short circuit, open circuit, or unbalanced resistance in the compressor internal permanent magnet synchronous motor (PMSM) three-phase windings, causing abnormal back electromotive force (BEMF); 2) Overcurrent, overheating, or power transistor breakdown in the controller internal IPM; 3) Transient spike in the high-voltage DC bus voltage (e.g., precharge failure or stuck HV battery relay); 4) Compressor mechanical seizure (e.g., scroll plate wear or lack of refrigerant oil) causing a sudden load increase and abnormal current and voltage rise.

This fault triggers a protective compressor shutdown, causes complete air conditioning system failure, and may affect battery thermal management (e.g., liquid cooling plate circulation).

This is a level 2 severe fault.

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Cases Logged
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Causes
Likely Causes — Qin Plus
  • 1Compressor internal motor winding fault: Unbalanced three-phase winding resistance (normal resistance approximately 0.5-1.0Ω, difference between any two phases less than 0.1Ω), or decreased winding-to-housing insulation resistance (below 20MΩ), causing abnormal phase voltage detection.
  • 2Compressor controller IPM module damaged: IGBT or MOSFET breakdown in the intelligent power module, or gate drive circuit failure. This fault typically presents with controller overheating, burn marks, or concurrent DTC B2AB249 (IPM IGBT fault).
  • 3High-voltage wiring harness and connector fault: Backed-out terminals, looseness, or water ingress and burn damage at the compressor high-voltage connector (B28/B29) increase contact resistance and generate voltage spikes; or damaged shielding causes electromagnetic interference.
  • 4Compressor mechanical system fault: Poor sealing, wear, or seizure of the scroll (common issue in early BYD batches), or degraded or insufficient refrigerant oil causing excessive mechanical load and triggering overvoltage protection.
  • 5Controller software or calibration issue: Outdated Compressor ECU software version, a bug in the phase voltage sampling algorithm, or overly sensitive high-voltage threshold calibration triggering a false DTC.
What To Do
  • 1
    Step 1 - Fault code reading and freeze frame analysis: Use a VDS or X431 diagnostic tool to read all DTCs. Confirm B2AB81C (or B2AB8-1C) and accompanying fault codes (such as B2AB249 IPM fault, B2AB997 overload, B2AB349 temperature sensor fault). Record freeze frame data (high voltage, compressor speed, inverter temperature, phase current values).
  • 2
    Step 2 - High-voltage safety and visual inspection: Disconnect the high-voltage service disconnect (MSD) and wait 5 minutes to allow the capacitors to discharge. Inspect the front compartment electric compressor high-voltage harness connectors (B28, B29) for looseness, backed-out pins, water ingress, burn marks, or corrosion. Inspect the controller heat sink for blockages and the controller mounting bracket for looseness.
  • 3
    Step 3 - Electrical parameter measurement: Reinstall the MSD and measure the insulation resistance between the compressor three-phase high-voltage wires and the housing (should be greater than 20MΩ). Disconnect power, then measure the three-phase winding resistance (U-V, V-W, and U-W should be balanced, with a difference less than 0.1Ω). Measure the controller low-voltage power supply (12V, range 11-14V) and the CAN-H/CAN-L line voltage (approximately 2.5V).
  • 4
    Step 4 - Software version check: Check the BYD Technical Service Bulletin (TSB) to verify the current compressor controller software is the latest version (e.g., V1.4 or higher). Prioritize a software update for intermittent faults with no hardware abnormalities.
  • 5
    Step 5 - Component-level replacement or repair: If measurements show winding imbalance or insulation failure, replace the electric compressor assembly. If only the wiring harness connector is burnt, replace the high-voltage wiring harness. If the controller hardware is damaged but the compressor itself is normal, replace the controller separately (4S dealerships usually require replacing the complete assembly to ensure warranty coverage).
  • 6
    Step 6 - System reset and refrigerant charging: After replacement, execute the Compressor Break-in procedure. Use a vacuum pump to evacuate the system for at least 30 minutes (vacuum level below -95 kPa). Charge the system with the standard amount of POE compressor oil (typically 120-150 ml, depending on vehicle model) and R134a refrigerant (450-600 g). Clear the fault codes and perform a road test to verify. Monitor the data stream to ensure the phase voltage remains stable within the 200-400 V range.
Real-World Cases
BYD DTC AI Analysis

BYD Han EV: Compressor motor winding short circuit causing excessive phase voltage

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Symptoms: While driving normally, the AC suddenly stopped cooling and the vents blew ambient air. The instrument cluster showed no warning lights, but the AC control panel worked normally. Diagnosis: VDS read DTC B2AB81C (phase voltage too high) along with B2AB249 (IPM IGBT fault). Checked high-voltage harness connectors B28/B29; no abnormalities found. Measured compressor low-voltage supply at 13.9V (normal). Disconnected power and measured three-phase winding resistance: U-V phase was 2.3Ω (normal ~0.8Ω) with unstable readings, confirming an internal inter-turn short in the motor. Solution: Replaced the electric compressor assembly (PN HCE-8103020C). Recovered the old oil and flushed the AC lines. Added 120ml POE refrigeration oil and 550g R134a refrigerant. Evacuated the system and performed a vacuum hold test. Fault resolved.
Original source ↗
BYD DTC AI Analysis

BYD Song Pro DM: Poor controller cooling causes intermittent fault

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Symptoms: Air conditioning intermittently stops working while driving, especially in heavy traffic or at highway speeds. Temporary recovery after shutdown and restart. Diagnosis: Retrieved stored DTCs B2AB8-1C (phase voltage high) and U0296 (communication lost with BMS, intermittent). Found the electric compressor controller mounting bracket loose, heat sink severely clogged with dust, and minor burn marks on the IPM module surface. Further inspection found loose contact at pin 3 of high-voltage connector B28. Repair: Re-tightened the controller mounting bracket, replaced the compressor high-voltage harness assembly (including the connector), and thoroughly cleaned the controller heat sink. Cleared DTCs, road-tested 50 km with no fault recurrence; live data showed phase voltage stable within normal range.
Original source ↗
BYD DTC AI Analysis

BYD Qin Plus DM-i: Worn scroll plates causing excessive load

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Symptoms: With the AC on, the compressor made a distinct buzzing noise. Cooling performance dropped sharply, the low-pressure lines frosted up, and the AC failed completely after about 5 minutes. Diagnosis: Read codes B2AB81C (phase voltage too high) and B2AB997 (compressor overload). Recovered 450g of refrigerant and found black compressor oil containing metal debris. Disassembled the compressor and found severe wear on the scroll plate surfaces. The seals between the orbiting and fixed plates were worn—a known batch defect in early BYD electric compressors caused by an internal seal design flaw that allows gas leakage and bypass. Resolution: Replaced the scroll plate assembly with an improved design (the manufacturer updated the parts with enhanced sealing). Thoroughly cleaned the condenser, evaporator, and lines, replaced the desiccant, and filled with fresh POE oil. The compressor now runs smoothly and pressures returned to normal (low 0.2–0.3MPa, high 1.4–1.6MPa).
Original source ↗
BYD DTC AI Analysis

BYD Yuan Plus: False Software Fault Warning on New Vehicle

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Symptoms: New vehicle, approximately 5000 km on the odometer. Air conditioning intermittently failed to cool. DTC B2AB8-1C appeared intermittently with no other associated faults. Fault cleared after switching off the ignition. Diagnosis: Comprehensive hardware inspection (wiring harness, connectors, compressor body, controller housing) found no abnormalities. Three-phase winding resistance measured balanced with good insulation. Consulted BYD Technical Service Bulletin (TSB); confirmed the compressor controller software version V1.2 on this batch contains a phase voltage sampling algorithm bug. Under specific conditions (high-voltage power-up instant or after fast charging), the system falsely reports excessive phase voltage. Resolution: Upgraded the compressor controller software to version V1.4 using the VDS diagnostic tool. Monitored continuously for one month after the upgrade. The DTC did not reappear and the air conditioning system operates normally.
Original source ↗
Other Qin Plus 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.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.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.B173A1ADTC B173A1A indicates the right middle-row side airbag (typically located on the side of the right second-row seat or inside the C-pillar trim panel) igniter circuit resistance measures 0 Ω. In the Supplemental Restraint System (SRS), normal airbag igniter resistance ranges between 2.0 and 5.0 Ω. A resistance of 0 Ω indicates a short to ground or a short between circuit wires, preventing the Airbag Control Unit (ACU) from establishing a normal monitoring circuit. This safety-critical fault prevents the airbag from deploying during a collision, continuously illuminates the instrument panel SRS warning lamp, and may force the entire airbag system into fail-safe mode.B173BDTC B173B indicates an abnormal electric A/C compressor speed feedback signal or a communication fault between the compressor controller and the motor. In BYD new energy models (e.g., Tang, Song, Qin, and Yuan series), this DTC belongs to the HVAC subsystem within the Body Control system and specifically involves the electric compressor closed-loop control circuit. The ECU sets this DTC when the compressor controller (IPM) fails to receive a valid pulse signal from the Hall speed sensor for more than 3 continuous seconds, or when the deviation between the detected actual speed and the target commanded speed exceeds the calibrated threshold (typically >500 rpm). This fault forces the A/C system into fail-safe mode and stops compressor operation. Symptoms include a complete lack of cooling, intermittent cooling, or a sharp decrease in cooling performance. The instrument cluster A/C warning lamp may also illuminate. Prolonged operation with this fault can degrade high-voltage system insulation or cause controller overcurrent damage.
Common problems reported for Qin Plus →Qin Plus 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.