AU
B2AB5-73

DTC B2AB5-73 indicates the electric air conditioning compressor (E-Compressor) failed its start-up self-check — Atto 8

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 Atto 8 indicates the electric air conditioning compressor failed its start-up self-check, so compressor operation may be blocked. Severity is medium because it can affect cabin cooling and battery thermal management, possibly causing reduced 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 — Atto 8
  • 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 and disable compressor startup.
  • 2Compressor controller internal IGBT or drive circuit fault: Power module damage on the controller PCB prevents three-phase AC output to drive the scroll plate, 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: Scroll plate mechanical seizure causes excessive startup current, triggering protection; or motor winding insulation resistance below 2 MΩ 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 compressor damage from starting under pressure.
What To Do
  • 1
    Read the complete DTC and freeze frame using the diagnostic tool: Use VDS or ED400 to read the data stream at the time of the fault, including ambient temperature, battery SOC, compressor target speed, actual speed, high-voltage bus voltage, and compressor current, to determine if 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). Inspect 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 precharge 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 precharge completion (no voltage fluctuation).
  • 4
    LIN bus waveform measurement: Use an oscilloscope to measure the compressor LIN line waveform. The normal waveform shows a 12V level (dominant 0V, recessive 12V). Check for a short to ground or 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 compressor internal insulation failure.
  • 6
    Refrigerant pressure and mechanical inspection: Connect a refrigerant pressure gauge to check if 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 if the scroll plate is seized.
  • 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

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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

✓
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 8 Fault Codes
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.B110A02DTC B110A02 indicates the thermal management master control unit (HVAC ECU) or body control module (BCM) failed to receive valid CAN data frames from the PM2.5 air quality sensor over consecutive communication cycles (typically 500ms per cycle). The sensor typically mounts at the HVAC unit air inlet or behind the glove box and transmits real-time particulate concentration data (unit: μg/m³) to the HVAC controller via the CAN bus. The fault is essentially a communication link layer timeout. Potential causes include physical layer wiring faults, sensor power supply failures, sensor internal MCU lockup, or CAN network topology damage. Although this non-critical fault does not directly affect driving safety, it disables the intelligent air purification strategy and the automatic fresh air/recirculation switching function. In extreme cases, it triggers a thermal management system degraded mode, limiting compressor power or fixing the air flap position.B110B07This fault code indicates abnormal operation of the internal air pump (sampling pump) in the PM2.5 air quality detection module. The PM2.5 detector uses the laser scattering principle to measure particulate concentration and requires a built-in air pump to draw ambient air into the detection chamber at a constant flow rate. The ECU sets this code when it detects an open or short in the air pump drive circuit, abnormal current (stall or free-running), or abnormal speed feedback. This fault causes the automatic air conditioning system to lose air quality sensing capability, preventing automatic switching between fresh air and recirculation modes. The instrument cluster air quality display may show '--' or a fixed value, but the fault does not affect the vehicle powertrain or basic air conditioning cooling and heating functions.B173CDTC B173C indicates the Supplemental Restraint System (SRS) detects the Right Second Row Side Airbag squib circuit resistance exceeds the calibrated threshold (typically >4.5Ω). This fault is an active diagnostic result of the SRS system, indicating a high-resistance condition in the circuit between the Airbag Control Unit (ACU) and the airbag module. Causes for excessive resistance include increased contact resistance, a partially broken wiring harness, terminal oxidation, or an aging squib wire inside the airbag module. This fault causes the system to mark the airbag circuit as 'unreliable', meaning the airbag may fail to deploy during a collision. The fault typically illuminates the instrument cluster airbag warning light (SRS light) continuously, and some models also sound a warning buzzer.
Common problems reported for Atto 8 →Atto 8 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.