AU
B2A0717

This DTC indicates the A/C controller or thermal management system control module detects a power supply voltage exceeding the 16V safety threshold — Seal U

Thermal Management System

This DTC indicates the A/C controller or thermal management system control module detects a power supply voltage exceeding the 16V safety threshold.

In BYD new energy vehicles, the DC-DC converter typically converts high-voltage traction battery energy to power the low-voltage system (12V/14V system).

Normal output voltage should range between 13.5V and 14.5V.

When the monitoring point voltage continuously exceeds 16V, the controller identifies an overvoltage condition and triggers a protection mechanism to prevent electronic component damage.

This fault may restrict A/C system functions, reduce thermal management efficiency, or force the system into a power derating mode.

Extreme cases may damage sensitive electronic components on the control board.

The '161' in the DTC typically refers to a specific voltage monitoring circuit or sensor number.

3
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1DC-DC converter output voltage regulation failure, causing the low-voltage side output voltage to rise abnormally above 16V.
  • 2Fault in the A/C controller internal power management chip or voltage sampling circuit, causing a false overvoltage report.
  • 312V low-voltage battery aging, sulfation, or poor connection causing voltage fluctuations and transient overvoltage spikes.
  • 4Alternator voltage regulator fault (for hybrid models equipped with a starter-generator), causing excessive charging voltage.
  • 5Poor contact, loose connection, or poor ground in the air conditioning controller power supply circuit causes the reference voltage at the sampling point to drift.
What To Do
  • 1
    Use the VDS2000/VDS1000 diagnostic tool to read all fault codes and freeze frame data. Record the specific voltage value and environmental conditions during the overvoltage event. Confirm whether B2A0717 is a current or history fault.
  • 2
    Measure the low-voltage battery static voltage (vehicle off) and dynamic voltage (OK power/Ready state). Confirm whether the actual DC-DC output voltage exceeds 16V to determine if this is a true overvoltage or a false sensor report.
  • 3
    Check the A/C controller fuse, relay, and power supply wiring connections. Specifically inspect the power and ground wires from the BMS compartment and front compartment power distribution box to the A/C controller for loose connections, oxidation, or burn damage.
  • 4
    Disconnect the air conditioning controller connector and measure the voltage between the controller-side power supply pin and ground. If the voltage is normal, replace the air conditioning controller assembly. If the voltage remains too high, inspect the DC-DC converter and upstream power distribution circuit.
  • 5
    Check the DC-DC converter output characteristics. If necessary, update the DC-DC control software or replace the DC-DC assembly. Verify the output voltage remains stable within the 13.8V-14.5V range.
  • 6
    After repairing or replacing the faulty component, clear the fault code, perform the air conditioning system self-check, and operate the system under various operating conditions (cooling/heating/MAX mode) for at least 15 minutes to verify the fault does not return.
Real-World Cases
BYD DTC AI Analysis

B2A0717 Overvoltage Fault: Basic Definition and Troubleshooting

✓
AC system or related control module logged voltage overvoltage fault, potentially restricting AC function, causing control panel anomalies, or triggering protective shutdown. VDS scan retrieved DTC B2A0717 (161 Voltage Overvoltage), localized to the power supply circuit. Measured supply voltage to relevant sensors and control module exceeded system calibration threshold (e.g., above 16V). Fix involved checking generator output, voltage regulation module and wiring; replacing the faulty voltage regulator or repairing shorts/poor connections causing the voltage anomaly.
Original source ↗
BYD DTC AI Analysis

BYD Air Conditioning Controller Abnormal Voltage Fault

✓
With the A/C on, the control panel intermittently goes black or displays "Please check air conditioning system". Cooling is intermittent and the system fault light comes on. VDS scanning revealed A/C controller fault codes (similar to B2A series power faults). Voltage measurements at the controller supply pins showed excessive fluctuation or sustained overvoltage, setting DTC B2A0717. Inspection of the power circuit found a failed voltage regulator module. Replaced the A/C controller power supply voltage regulator module, repaired the harness contact issues, and cleared the codes. System returned to normal.
Original source ↗
BYD DTC AI Analysis

BYD New Energy Vehicle High Voltage Interlock Loop Voltage Fault

✓
Dashboard shows "EV Function Limited" or "Check Powertrain". Vehicle cannot enter EV mode and intermittently fails to ready up. VDS scan reveals voltage-related DTCs in the BMS or HVAC thermal management system (refer to B2A series). Check the power wiring between the high voltage distribution box and AC controller; overvoltage present. Voltage at sensor No. 161 or the control point measures outside the normal range. Check DC-DC converter output voltage. Replace the damaged fuse or relay in the high voltage distribution box. Repair the AC controller power supply wiring. Fault resolved.
Original source ↗
Other Seal U 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.