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U2ABC16

DTC U2ABC16 indicates the electric air conditioning compressor high-voltage load circuit detects an input voltage below the normal operating threshold (typically below 420VDC) — Atto 3

Thermal Management System

DTC U2ABC16 indicates the electric air conditioning compressor high-voltage load circuit detects an input voltage below the normal operating threshold (typically below 420VDC).

In the 2019 BYD Qin EV thermal management system, the high-voltage battery pack (nominally 500V+) powers the electric compressor through the high-voltage power distribution box.

This fault indicates the compressor controller detects insufficient bus voltage to maintain normal compressor startup or operation during self-check or running.

This fault triggers a protective compressor shutdown, causing air conditioning cooling failure.

In extreme cases, it may affect battery thermal management (liquid cooling system), but typically does not directly cause a vehicle breakdown.

The root cause involves an abnormality in the high-voltage power supply circuit, Battery Management System (BMS) voltage monitoring, or the compressor controller internal voltage sampling circuit.

5
Cases Logged
Real-World Cases
BYD DTC AI Analysis

Qin EV air conditioning suddenly stopped working while driving

✓
Driving normally when the AC suddenly blew hot air. No warning lights on the dash, but the AC panel was flashing. Scanned DTC U2ABC16. Freeze frame showed bus voltage at 398V and SOC at 35% when the fault occurred. Further inspection found cell 12 in the battery pack at only 2.8V while the remaining cells read 3.3V—a 500mV difference. This undervoltage caused the BMS to limit power output, and the drop in bus voltage triggered compressor protection. Replaced the module and performed a balancing charge. Fault resolved.
BYD DTC AI Analysis

High-voltage distribution box contactor burn damage caused intermittent fault

✓
Intermittent AC cooling failure; recovered after key cycle. DTC U2ABC16 logged intermittently. Static voltage at the compressor HV terminal: 500V (normal), but dropped to 380V instantly when AC engaged. Removed the HV distribution box and found severe burning on the compressor positive contactor contacts. Contact resistance: 2.3Ω (normal <0.1Ω). Replaced the HV distribution box assembly (part number: KAD-2152410). Loaded voltage now stays above 495V. Fault has not returned.
BYD DTC AI Analysis

Compressor controller pre-charge circuit failure

✓
Air conditioning shut off automatically within 10 seconds of power-on, logging DTC U2ABC16. Compressor controller bus voltage measured only 280 V at power-on, far below the normal pre-charge target (>450 V). Pre-charge relay tested normal, but the pre-charge resistor read infinite resistance (on the Qin EV, this resistor sits inside the battery pack). Disassembled the battery pack and replaced the pre-charge resistor (30 Ω). Inspection also revealed capacitor aging inside the compressor controller; replaced the compressor controller as well. Fault resolved.
BYD DTC AI Analysis

High voltage harness pin backed out causing intermittent connection.

✓
The air conditioning cut out frequently on rough roads but worked normally on smooth surfaces. Inspection revealed the compressor power pin in the high-voltage connector (large orange plug) between the battery pack and high-voltage distribution box had backed out approximately 1 mm, with burn marks on the socket. Driving vibration caused poor contact, instantly increasing line resistance, and the compressor controller detected the voltage drop. Replaced the high-voltage wiring harness connector, applied conductive paste, and tightened the plug to resolve the fault.
BYD DTC AI Analysis

BMS voltage sampling drift false positive

✓
At SOC 100%, turning on the AC immediately set DTC U2ABC16. Battery pack voltage measured 512V and compressor-side voltage 508V — both normal. Scan tool showed BMS compressor bus voltage at 395V. Fault traced to internal BMS voltage sampling circuit or voltage divider resistor, causing incorrect voltage data to the compressor controller. Replaced the battery management unit (BMS main unit, located inside the battery pack or cabin depending on configuration), flashed BMS software. Fault cleared.
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.