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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 — Seal U

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 — Seal U
  • 1Compressor internal motor winding fault: Unbalanced three-phase winding resistance (normal resistance approx. 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: Shorted IGBT or MOSFET in the intelligent power module, or gate drive circuit fault; usually presents with controller overheating, burn marks, or DTC B2AB249 (IPM IGBT fault).
  • 3High-voltage wiring harness and connector fault: Backed-out terminals, looseness, water ingress, or 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/missing compressor oil causing excessive mechanical load and triggering overvoltage protection.
  • 5Controller software or calibration issue: Outdated Compressor ECU software version, phase voltage sampling algorithm bug, or overly sensitive high-voltage threshold calibration causing a false fault.
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 any 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 manual 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 cables 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 voltage (approximately 2.5V).
  • 4
    Step 4 - Software version check: Check the BYD Technical Service Bulletin (TSB) to confirm 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 body is normal, try replacing the controller separately (authorized dealers typically require replacing the complete assembly to maintain the warranty).
  • 6
    Step 6 - System Reset and Refrigerant Charging: After replacement, perform the Compressor Break-in procedure. Evacuate the system using a vacuum pump for at least 30 minutes (vacuum below -95 kPa). Charge the system with the standard amount of POE refrigerant oil (usually 120-150 ml, depending on vehicle model) and R134a refrigerant (450-600 g). Clear the fault codes and perform a road test for verification. Monitor the data stream to confirm 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 Seal U 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.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.
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.