AU
B2AB5-73

DTC B2AB5-73 indicates the electric air conditioning compressor (E-Compressor) failed its start-up self-check — Seal 6 EV

Thermal Management System

DTC B2AB5-73 indicates the electric air conditioning compressor (E-Compressor) failed its start-up self-check.

The compressor controller (Inverter) generates this fault if it receives a start command from the VCU (Vehicle Control Unit) but fails to establish normal speed feedback or a normal high-voltage DC bus within the specified time (usually 3-5 seconds).

Technical causes include abnormalities in the high-voltage interlock (HVIL) circuit integrity, DC bus pre-charge logic, compressor motor phase current detection, or the LIN bus communication handshake protocol.

In the BYD thermal management system, this compressor handles both cabin air conditioning and battery pack liquid cooling/heating functions.

When this fault triggers, the system inhibits compressor operation.

This inhibition can cause battery thermal management failure, subsequently triggering power limitation (reduced-power driving) or preventing high-voltage power-up.

The B2AB5-73 fault code on the Seal 6 EV indicates the electric A/C compressor failed its start-up self-check. This is a medium-severity issue because it can affect cabin cooling and battery thermal management, possibly limiting power. Common causes include a poor high-voltage interlock connector contact or an internal compressor controller fault. 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
  • 1High-voltage interlock loop (HVIL) pin backed out or corroded: Poor contact at the compressor high-voltage connector interlock pin causes the vehicle control unit to detect an incomplete high-voltage circuit, preventing the compressor from starting.
  • 2Internal IGBT or drive circuit fault in the compressor controller: A damaged power module on the controller PCB fails to output three-phase AC to drive the scroll, resulting in high-voltage input but no current output.
  • 3LIN bus communication fault: Short circuit, open circuit, or signal interference in the LIN wiring harness between the compressor controller and the air conditioning controller (AC ECU) prevents speed command transmission or causes feedback signal loss.
  • 4Compressor mechanical seizure or insulation failure: Mechanical seizure of the scroll causes excessive start-up current and triggers protection, or motor winding insulation resistance below 2MΩ triggers leakage protection.
  • 5Abnormal refrigerant pressure protection: When high-side pressure exceeds 3.2 MPa or low-side pressure drops below 0.18 MPa, the pressure switch cuts off the start signal to prevent starting under pressure from damaging the compressor.
What To Do
  • 1
    Read the complete DTC and freeze frame data using the diagnostic tool: Use VDS or ED400 to read data streams from when the fault occurred, including ambient temperature, battery SOC, compressor target speed, actual speed, high-voltage bus voltage, and compressor current. Determine if the fault is intermittent.
  • 2
    High-voltage interlock circuit inspection: Disconnect the compressor high-voltage connector. Measure continuity between the HVIL circuit pins (should be less than 1Ω). Check the connector for backed-out pins, burn marks, or signs of water ingress. Clean or replace the wiring harness if necessary.
  • 3
    High-voltage power supply and pre-charge check: Power on the vehicle and measure the voltage between the positive and negative terminals of the compressor high-voltage connector. The voltage must equal the traction battery voltage (normal range 320V-700V). Verify the pre-charge is complete (no voltage fluctuation).
  • 4
    LIN bus waveform measurement: Use an oscilloscope to measure the compressor LIN line waveform. The normal level is 12V (dominant 0V, recessive 12V). Check for a short to ground or short to power.
  • 5
    Insulation resistance test: Use a megohmmeter (1000V range) to measure the insulation resistance between the compressor high-voltage positive/negative terminals and body ground. The standard value must be greater than 20MΩ. A reading below 2MΩ indicates internal compressor insulation failure.
  • 6
    Refrigerant pressure and mechanical check: Connect a refrigerant pressure gauge to verify the high and low-side pressures are within the normal range (static pressure approximately 0.6-0.8 MPa). Manually rotate the compressor clutch (if equipped) or check the scroll plate for binding.
  • 7
    Component Replacement Verification: If the above checks are normal, replace the compressor controller (if replaceable separately) or the complete electric compressor assembly. Evacuate and recharge the refrigerant (standard amount: 450-550g R410a).
Real-World Cases
BYD DTC AI Analysis

Worn compressor LIN harness causes intermittent startup failure on Qin PRO DM

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A 2018 Qin PRO DM with 62,000 km. The instrument cluster intermittently displayed "Thermal Management System Fault" and the air conditioning intermittently stopped cooling. VDS read code B2AB5-73; freeze frame showed compressor speed at 0 rpm when the fault occurred. High voltage supply tested normal. The LIN line showed resistance to ground occasionally dropping to 0.5 Ω. Lifted the vehicle and found the compressor LIN wiring harness rubbing against the front subframe; damaged insulation caused an intermittent short to ground. Repaired the harness and re-secured the routing. Fault resolved.
BYD DTC AI Analysis

Qin EV300: Backed-out HVIL pin prevented compressor from starting

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2017 BYD Qin EV300 with no AC cooling. Retrieved DTC B2AB5-73. Inspected the compressor high-voltage connector and found one HVIL (High Voltage Interlock Loop) shorting pin completely backed out, causing the vehicle controller to detect an incomplete high-voltage circuit. Re-crimped the pin, applied conductive paste, and fully seated the connector. Fault code cleared, compressor started normally, and HVIL resistance returned to normal (less than 1 Ω).
BYD DTC AI Analysis

Compressor controller IGBT breakdown caused Qin PRO EV startup failure

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2019 Qin Pro EV. Air conditioning suddenly stopped working while driving, accompanied by a 'motor overheating' warning. The diagnostic tool reported B2AB5-73 and B2AB41D (internal overcurrent). Disassembled the compressor controller and found the upper and lower bridge arms of one phase in the IGBT module had shorted, triggering immediate overcurrent protection once pre-charge completed. Replaced the compressor assembly (integrated controller and motor design), recharged the refrigerant, and fixed the fault. Poor controller cooling caused the power devices to overheat and fail.
BYD DTC AI Analysis

Insufficient refrigerant triggered low-pressure protection (B2AB5-73).

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2019 Qin PRO DM — AC shuts down shortly after startup. Scanned DTC B2AB5-73. Live data showed low-side pressure at 0.12MPa when the fault occurred, below the 0.18MPa protection threshold. Found micro-leak at condenser fitting; refrigerant charge at 30% of spec. Repaired leak, evacuated system and recharged with 500g R410a and refrigerant oil. Fault cleared. Analysis: Severe refrigerant loss triggered low-pressure protection immediately on compressor startup; consecutive failed start attempts set this DTC.
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.