AU
B2AB8-1C

DTC B2AB8-1C (abbreviated from B2AB81C) indicates the Electric A/C Compressor controller detected an abnormally high three-phase drive voltage — Seal 6 EV

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.

The B2AB8-1C fault code on the Seal 6 EV indicates the electric A/C compressor controller has detected abnormally high three-phase drive voltage. This is a medium-severity fault that shuts down the compressor and can affect cabin cooling and battery thermal management. Common causes include a faulty compressor motor winding or a damaged IPM/IGBT drive circuit. 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 6 EV
  • 1Compressor internal motor winding fault: Three-phase winding resistance imbalance (normal resistance approx. 0.5-1.0Ω, difference between any two phases must be 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 typically presents with controller overheating, burn marks, or a concurrent B2AB249 (IPM IGBT fault).
  • 3High-voltage wiring harness and connector fault: Backed-out terminals, looseness, or water ingress and burn damage at compressor high-voltage connector (B28/B29) increases contact resistance and generates 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/missing compressor oil causing excessive mechanical load and triggering overpressure protection.
  • 5Controller software or calibration issue: Outdated Compressor ECU software version, phase voltage sampling algorithm bug, 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 complete 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 (HV 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. Check the front compartment electric compressor high-voltage wiring harness connectors (B28, B29) for looseness, backed-out pins, water ingress, burn marks, or corrosion. Check the controller heat sink for blockages and the controller mounting bracket for looseness.
  • 3
    Step 3 - Electrical parameter measurement: Refit the MSD and measure the insulation resistance between the compressor three-phase high-voltage wires and the housing (must be greater than 20MΩ); disconnect the power, then measure the three-phase winding resistance (U-V, V-W, and U-W must be balanced, with a difference of less than 0.1Ω); measure the controller low-voltage power supply (12V, range 11-14V) and the CAN-H/CAN-L line voltages (approximately 2.5V).
  • 4
    Step 4 - Software version check: Consult the BYD Technical Service Bulletin (TSB) to confirm the compressor controller has the latest software 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 body is normal, replace the controller separately (4S dealerships typically require replacing the complete assembly to maintain 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 below -95 kPa). Charge POE compressor oil (usually 120-150 ml, depending on vehicle model) and R134a refrigerant (450-600 g) to specification. Clear the fault codes and perform a road test. Monitor the data stream to verify the phase voltage stabilizes 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.
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Other Seal 6 EV 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.B1737DTC B1737 indicates the Supplemental Restraint System (SRS) detected abnormal continuity between the right middle-row side airbag squib circuit (typically the second-row right seat side airbag or right curtain airbag) and the vehicle power supply (B+, battery positive). The SRS ECU monitors the airbag inflator resistance via an internal current source (normal resistance: 2.0–3.0 Ω). If the ECU detects the voltage across the inflator circuit remaining close to battery voltage (>5 V and approaching 12 V) instead of the expected low potential or floating state, it identifies a short to power. This fault prevents the airbag from deploying normally during a collision because the short circuit bypasses the firing current. In extreme cases, abnormal current can cause unintended deployment, posing a severe safety hazard.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 Seal 6 EV →Seal 6 EV 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.