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U2ABB17

DTC U2ABB17 indicates the electric compressor controller (PCU) detects the input DC high voltage exceeds the permitted operating threshold (typically 110%-120% of the rated voltage) — Atto 3

Thermal Management System

DTC U2ABB17 indicates the electric compressor controller (PCU) detects the input DC high voltage exceeds the permitted operating threshold (typically 110%-120% of the rated voltage).

For example, on the 2019 Qin EV, the system triggers this fault when the high-voltage battery pack voltage exceeds approximately 420-450V or the compressor internal bus voltage reading exceeds the safe range.

This fault acts as a high-voltage safety protection mechanism for the thermal management system.

Upon detecting abnormally high voltage, the compressor actively disconnects the high-voltage relay to protect the IGBT power module and motor insulation.

Actual battery pack overvoltage, voltage sampling circuit drift, high-voltage interlock circuit faults, or control software logic errors can cause this fault.

Determine whether the condition is a genuine voltage abnormality or a signal detection fault.

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Cases Logged
Real-World Cases
BYD DTC AI Analysis

Air Conditioning Failure After Fast Charging

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A 2019 Qin EV was fast-charged to 98% on a 120kW DC charger during winter in the north. The AC then failed to cool. DTC U2ABB17 logged. Freeze frame data showed the compressor reading 452V while the actual battery pack voltage was 438V. Replaced the compressor controller, but the fault remained. Eventually traced this to outdated BMS software (Ver 3.2) with a faulty voltage sampling compensation algorithm at high SOC. Flashed the BMS to Ver 4.1. The compressor then received correct voltage data and the fault cleared.
BYD DTC AI Analysis

Loose connection in compressor high-voltage harness triggered overvoltage protection

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While driving normally, the air conditioning suddenly stopped working and the dashboard displayed "Thermal Management System Fault". Found intermittent DTC U2ABB17. Checked the compressor high-voltage connector (BYD standard blue plug); the internal HV+ terminal had backed out approximately 2mm, increasing contact resistance to 0.8Ω (normal <0.1Ω). Arcing and voltage spikes during compressor start/stop triggered overvoltage protection. Re-crimped the terminal and applied high-voltage silicone grease; contact resistance dropped to 0.05Ω and the fault cleared.
BYD DTC AI Analysis

Voltage sampling circuit resistor aging

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After the vehicle sat overnight, DTC U2ABB17 set immediately on first start and the air conditioning would not turn on. Measured battery pack voltage at 386V (normal), but live data showed compressor detected voltage at 468V, indicating a sampling circuit fault. Removed the compressor controller (located on top of the compressor) and measured the high-voltage sampling voltage divider resistor network. Found R15 (2MΩ/1%) had drifted to 2.4MΩ, causing incorrect voltage division. Replaced the precision resistor; sampling value returned to normal (387V), fault resolved.
BYD DTC AI Analysis

High regeneration during extended downhill driving caused momentary overvoltage

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After a 10 km long downhill mountain drive, the air conditioning stopped working and the 'Power System Fault' warning light illuminated. DTCs read U2ABB17 and related BMS overvoltage codes. Data analysis showed the battery pack voltage spiked from 410 V to 463 V at the moment of failure—high regenerative braking and high internal resistance from cold ambient temperatures caused the spike. Inspection of the BMS and compressor software revealed the compressor overvoltage protection threshold was set at 460 V, while the battery pack allowable charge voltage is 465 V. The threshold was too sensitive. Upgraded the thermal management controller software, raising the overvoltage protection threshold to 475 V and optimizing the delay strategy. Issue resolved.
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: Community This information is for reference only. Always consult a qualified technician for diagnosis and repair. Do not attempt high-voltage system repairs yourself.