AU
B2AB997

DTC B2AB997 indicates the electric air-conditioning compressor (E-Compressor) operating load exceeds the system-calibrated safety threshold — Atto 8

Thermal Management System

DTC B2AB997 indicates the electric air-conditioning compressor (E-Compressor) operating load exceeds the system-calibrated safety threshold.

The compressor controller or vehicle control unit (VCU) triggers this fault in the BYD Qin EV thermal management system when it detects a compressor drive current continuously exceeding the rated value (typically >15-20A, depending on operating conditions), an abnormal drop in speed feedback (stall risk), or an abnormal rise in torque demand.

The system then registers an 'excessive load'.

This protective fault prevents compressor mechanical damage, high-voltage circuit overload, or thermal management system failure.

The fault can reduce air-conditioning cooling capacity and automatically shut down the compressor.

Extreme cases may trigger high-voltage interlock protection, affecting battery thermal management functions.

5
Cases Logged
5
Causes
Likely Causes — Atto 8
  • 1Electric compressor internal mechanical seizure or lubrication failure: scroll plate wear, bearing seizure, degraded or insufficient refrigerant oil, resulting in increased mechanical resistance torque.
  • 2Abnormal air conditioning system pressure: high condenser pressure (dirty or blocked condenser, cooling fan fault, high ambient temperature), low evaporator pressure (expansion valve fault, line blockage), or refrigerant overcharge (excess liquid refrigerant creates risk of liquid slugging).
  • 3High-voltage power supply system fault: Unstable traction battery voltage (undervoltage or overvoltage), poor contact in high-voltage wiring harness (burnt or loose connectors causing increased resistance), compressor controller (IPM) power module fault
  • 4Poor heat dissipation in the thermal management system: severely contaminated front-end module (condenser + radiator), abnormal electric fan speed (PWM signal fault or motor aging), or restricted coolant circulation causing compressor overheating.
  • 5Control strategy or sensor fault: compressor phase current sensor drift, CAN bus communication fault causing VCU to misjudge load, or software calibration parameter error.
What To Do
  • 1
    Fault confirmation and data reading: Use the VDS2000/VDS3000 diagnostic tool to read all fault codes and confirm B2AB997 is a current fault. Read the data stream, monitoring compressor current (A), speed (rpm), duty cycle (%), high-voltage bus voltage (V), A/C high-side pressure (MPa), and condenser outlet temperature (°C).
  • 2
    High-voltage safety check: Perform the high-voltage power-down procedure, wear insulated gloves, measure the compressor high-voltage wiring harness insulation resistance (standard value ≥20MΩ), check the high-voltage connectors (B23/B24) for burn marks or backed-out pins, and measure the contact resistance (should be <0.1Ω).
  • 3
    Refrigeration system pressure check: Connect the manifold gauge set. Check the static pressure (approximately 1.0-1.2MPa at 25°C). Check the dynamic high-side pressure (1.5-2.5MPa, depending on ambient temperature) and low-side pressure (0.15-0.25MPa). Verify if the high-side pressure is excessively high or the low-side pressure is excessively low.
  • 4
    Compressor mechanical inspection: Disconnect the high-pressure and low-pressure pipes. Check the compressor rotational resistance (manually turn the clutch plate; it must rotate smoothly without binding, resistance torque <3N·m). Check the refrigerant oil condition (colour, impurities, quantity). If necessary, use dedicated equipment to test the compressor insulation (>20MΩ) and coil resistance (three-phase balance, deviation <10%).
  • 5
    Thermal management cooling system inspection: Clean the condenser surface (use a dedicated cleaning agent to avoid damaging the cooling fins), check the electric fan high and low-speed operation (low speed approx. 1000 rpm, high speed approx. 2000 rpm), and check the coolant level and circulation (electronic water pump operation).
  • 6
    Control module and wiring inspection: Measure the compressor controller low-voltage power supply (12V±0.5V) and ground (<0.1Ω). Check CAN-H and CAN-L voltages (2.5V±0.5V) and waveforms (dominant level: CAN-H 3.5V / CAN-L 1.5V) to rule out short or open circuits in the wiring.
  • 7
    Repair verification: After repairing or replacing the faulty component, evacuate the system (maintain -0.1 MPa for 30 minutes), charge the refrigerant to specification (R134a, usually 550-650g), and perform the compressor run-in procedure (gradually increase speed). Observe the data stream during a road test to confirm the current stabilizes within the normal range (5-12A) and the fault code does not return.
Real-World Cases
BYD DTC AI Analysis

Qin EV 2019: Worn compressor scroll plate causing excessive load

✓
Vehicle: 2019 BYD Qin EV, 85,000 km. Symptoms: Approximately 5 minutes after turning on the AC, the vents blew warm air and the thermal management warning light illuminated. Retrieved DTC B2AB997. Diagnosis: Live data showed compressor current spiking to 25 A (normal ≤15 A) before the system shut down. Static pressures read normal, but dismantling the compressor revealed severe wear to the scroll plates, with internal metal debris causing mechanical seizure. Repair: Replaced the electric compressor assembly. Flushed the AC lines, condenser and evaporator with dedicated cleaner, and replaced the desiccant. Recharged the system with refrigerant and compressor oil (SP-A2 oil, 150 ml) to specification. Fault resolved.
BYD DTC AI Analysis

Severely clogged condenser caused excessive high-side pressure

✓
Vehicle: Qin EV 2019, 60,000 km, used year-round on construction sites. Symptoms: AC kept shutting down in hot summer weather. Scanner logged DTC B2AB997. Diagnosis: Data stream showed 38°C ambient with condenser outlet at 85°C (normal <65°C). High-side pressure read 3.2 MPa (normal 2.0–2.5 MPa) and compressor current stayed above 18 A. Found the condenser completely clogged externally with mud and willow fluff. The cooling fan ran at high speed but couldn't dissipate heat properly. Fix: Thoroughly cleaned the condenser fins (used a fin comb to straighten deformed fins), replaced the cabin filter, and cleaned the gap between the radiator and condenser. Cleared the codes; system returned to normal.
BYD DTC AI Analysis

Poor contact in high-voltage wiring harness caused abnormal load.

✓
Vehicle: BYD Qin EV 2019, accident-repaired vehicle. Symptom: Intermittent AC cooling failure, intermittent DTC B2AB997. Diagnosis: Data stream showed high voltage bus voltage dropping instantly from 420V to 380V when the compressor engaged, with large current fluctuations. Inspection found burn marks inside high voltage harness connector B23 (front compartment high voltage distribution box to compressor). Contact resistance measured 2.3Ω (normal <0.05Ω), causing insufficient input voltage to the compressor controller. The controller increased current to maintain power, triggering overload protection. Repair: Replaced high voltage harness assembly, cleaned contacts and applied conductive paste, tightened connector. Fault resolved.
BYD DTC AI Analysis

Refrigerant overcharge causing liquid slugging risk

✓
Vehicle: Qin EV 2019. Fault appeared after a workshop topped up the refrigerant. Symptoms: Compressor noise when the AC turned on, followed by DTC B2AB997 and shutdown. Diagnosis: Recovery yielded 850g of refrigerant (standard: 600g). High-side pressure hit 2.8MPa at 25°C ambient. Compressor drew 16A. Liquid refrigerant entered the compressor before fully evaporating, causing liquid slugging and high mechanical load. Solution: Recovered all refrigerant and recharged to the standard 600g±25g. Replaced the receiver drier (liquid may have entered). Compressor load returned to normal.
BYD DTC AI Analysis

Compressor controller IPM module fault

✓
Vehicle: Qin EV 2019, 42,000 km. Symptoms: AC not cooling at all. Throwing B2AB997 and B2AB809 (compressor drive fault). Diagnosis: Measured compressor three-phase winding resistance balanced at 0.8 Ω; insulation normal. Controller low-voltage supply and signals normal. Internal IPM (Intelligent Power Module) in the controller failed, distorting the output current waveform and causing the phase current sensor to detect abnormally high current. Repair: Replaced compressor controller (some variants require the complete compressor assembly depending on configuration). Flashed control program to V2.3.1. Fault resolved.
Other Atto 8 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.