AU
B2AB5-73

DTC B2AB5-73 indicates the electric air conditioning compressor (E-Compressor) failed its start-up self-check — Atto 3

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.

4
Cases Logged
5
Causes
Likely Causes — Atto 3
  • 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 compressor startup.
  • 2Compressor controller internal IGBT or drive circuit fault: A damaged power module on the controller PCB prevents three-phase AC output to drive the scroll plate, resulting in high-voltage input with 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: Scroll plate mechanical seizure causes excessive startup current, triggering protection, or motor winding insulation resistance drops below 2 MΩ, triggering 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 the data streams recorded when the fault occurred, including ambient temperature, battery SOC, compressor target speed, actual speed, high-voltage bus voltage, and compressor current, to determine whether the fault is intermittent.
  • 2
    High-voltage interlock circuit check: Disconnect the compressor high-voltage connector and measure continuity between the HVIL circuit pins (should be less than 1 Ω). 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: With the vehicle powered on, 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 pre-charge completion (no voltage fluctuation).
  • 4
    LIN bus waveform measurement: Use an oscilloscope to measure the compressor LIN line waveform. The normal waveform is 12V (dominant 0V, recessive 12V). Check for a short to ground or a 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 exceed 20 MΩ. A reading below 2 MΩ indicates internal compressor insulation failure.
  • 6
    Refrigerant pressure and mechanical inspection: Connect a refrigerant pressure gauge to check if the high- and low-pressure 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

✓
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

✓
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

✓
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).

✓
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 Atto 3 Fault Codes
P0A0DBattery Energy Control Module Requested MIL IlluminationP0AA6Hybrid Battery Voltage System Isolation FaultP1A00Drive Motor "A" Performance — BYD proprietaryB1108For 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.
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.