AU
B2A5911

This DTC indicates a short to chassis ground (GND) in the signal circuit of the driver-side Foot Outlet Temperature Sensor — Qin Plus

Thermal Management System

This DTC indicates a short to chassis ground (GND) in the signal circuit of the driver-side Foot Outlet Temperature Sensor.

In the BYD thermal management system, this NTC thermistor sensor monitors the actual temperature at the foot air duct outlet.

The signal voltage is typically a 0-5V analog signal.

A short to ground causes the ECU to continuously read an abnormally low voltage near 0V, registering a corresponding temperature of -40℃ or an extreme low.

This forces the air conditioning control unit into fault protection mode.

The system may force the compressor off, switch to demist mode, or restrict battery coolant flow.

These conditions severely impact occupant comfort and battery/motor thermal management efficiency.

In extreme cases, this triggers high-voltage system overheat protection.

The B2A5911 fault code on the Qin Plus indicates a high-severity short to chassis ground in the driver-side foot outlet temperature sensor signal circuit. The AC control unit may read an extreme low temperature and enter protection mode, affecting cabin comfort and thermal management. Common causes include a failed thermistor or worn wiring insulation contacting the body. Visit an authorised dealer for diagnosis and repair. Typical repair cost data is available from recorded cases.
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Cases Logged
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Causes
Likely Causes — Qin Plus
  • 1The thermistor inside the sensor body breaks down and short-circuits, causing continuity between the signal and ground terminals.
  • 2Vibration wears through the wiring harness insulation where it passes through the dashboard or floor, causing the signal wire (usually yellow/green or blue/white) to contact the metal body frame.
  • 3Condensation leaking inside the A/C duct causes a short circuit or corrosion between the sensor connector pins (usually located on the duct housing).
  • 4Metal components such as seat rails and pedal brackets pinched or cut the floor wiring harness after adjustment, causing the signal wire to short to ground.
  • 5Internal signal processing circuit fault in the air conditioning control module (AC ECU) causes an abnormal drop in input impedance, creating a short to ground.
What To Do
  • 1
    Use the VDS2000/3000 diagnostic tool to read the complete fault code stream. Confirm B2A5911 is a current fault (Present), not a history fault. Check if 'driver footwell temperature' in the data stream displays -40°C, 0°C, or a fixed extremely low value.
  • 2
    Remove the driver-side footwell air outlet trim panel and locate the temperature sensor (usually on the lower surface of the air duct, 2-pin connector). Inspect the connector for looseness, water ingress, or obvious corrosion. Measure the sensor resistance (normal: approx. 1.8-2.2 kΩ at 25°C; close to 0 Ω if shorted to ground).
  • 3
    Disconnect the sensor connector and use a multimeter to measure the resistance between the wiring harness side signal pin (B+) and body ground. If the resistance is less than 5 Ω, this confirms a wiring harness short to ground. If the resistance is infinite, the fault is in the sensor itself.
  • 4
    If the wiring harness is short-circuited, visually inspect the harness routing under the instrument panel and along the floor. Closely check the harness sheathing integrity where it passes through the firewall, near the seat rails, and in the pedal bracket area. Look for points of wear, crushing, or damaged insulation.
  • 5
    Repair the wiring harness: Insulate the damaged area with heat-shrink tubing or waterproof tape. Re-secure the wiring harness to prevent contact with sharp metal. If the sensor is faulty, replace it with an OEM temperature sensor (usually labeled '温度传感器' or 'Foot Temp Sensor').
  • 6
    After restoring the connection, use the diagnostic tool to perform 'A/C system self-learning' or 'temperature sensor calibration' (if available in the menu). Clear the fault code. Monitor the data stream to verify the displayed temperature changes normally during A/C operation (typical range: -30°C to +60°C).
  • 7
    Perform a road test or static test to verify the fault code does not return. Confirm the footwell air outlet temperature control operates normally and the system triggers no abnormal protection modes.
Real-World Cases
BYD DTC AI Analysis

Song MAX seat rails crushed wiring harness, causing intermittent short circuit

✓
A 2018 Song MAX DM repeatedly set DTC B2A5911, with the warning light appearing intermittently. The fault consistently reproduced when adjusting the driver's seat to the rearmost position. Removing the seat revealed the floor wiring harness pinched at a seat rail mounting bolt; damaged insulation caused an intermittent short to ground. Rerouted the harness and secured it with dedicated wiring clips, positioning it clear of the seat track travel. Fault eliminated.
BYD DTC AI Analysis

Qin EV sensor body thermistor aging breakdown

✓
2017 Qin EV300 with poor AC cooling and DTC B2A5911. Sensor resistance measured only 12Ω (normal approx 2kΩ), confirming internal thermistor short. Replaced the driver's footwell temperature sensor (located at the lower section of the HVAC unit; requires removal of the lower glovebox trim panel). Live data shows normal temperature and automatic climate control restored.
BYD DTC AI Analysis

Qin Pro DM AC duct poor sealing causing condensate corrosion

✓
The 2019 Qin Pro DM frequently set DTC B2A5911 during the rainy season. Inspection found the evaporator housing seal had perished, allowing condensate to leak into the sensor mounting hole and oxidise and short the connector pins. Replaced the evaporator housing gasket, cleaned the connector terminals and applied conductive grease, and relocated the sensor to a higher position to avoid water pooling.
BYD DTC AI Analysis

Song MAX instrument panel wiring harness chafing against bracket

✓
A 2019 Song MAX with 80,000 km set DTC B2A5911 with no warm air at the driver's footwell. Removed the lower dashboard trim and found the temperature sensor wiring harness chafed through at the steering column mounting bracket from prolonged vibration, exposing copper conductors contacting the bracket. Repaired the harness, added a rubber protective sleeve and cable ties at the interference point, and ensured >10 mm clearance from metal components.
BYD DTC AI Analysis

Misdiagnosis of internal circuit fault in Qin PRO EV AC ECU

✓
After replacing the battery pack on a 2019 Qin Pro EV, DTC B2A5911 set, but the sensor and wiring harness tested normal. Further inspection revealed the AC control module (located in the centre of the dashboard) was crushed during removal and installation, damaging the internal signal acquisition circuit and causing a short to ground. Replacing the AC control module and reconfiguring the thermal management parameters resolved the fault.
Other Qin Plus 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.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.B110BDTC B110B indicates a fault in the internal air pump (sampling pump) of the PM2.5 air quality detector. This pump draws cabin or outside air into the PM2.5 sensor detection chamber, enabling the laser scattering sensor to measure real-time particulate matter concentration. The air conditioning controller (or BCM) sets this DTC upon detecting an open or short circuit in the pump drive circuit, or abnormal current caused by a seized pump motor. This fault disables the "Green Clean" system, causes the instrument cluster air quality display to read abnormally or disappear, and disables the automatic fresh air/recirculation switching function. It does not affect the vehicle powertrain or core thermal management functions.B173A1ADTC B173A1A indicates the right middle-row side airbag (typically located on the side of the right second-row seat or inside the C-pillar trim panel) igniter circuit resistance measures 0 Ω. In the Supplemental Restraint System (SRS), normal airbag igniter resistance ranges between 2.0 and 5.0 Ω. A resistance of 0 Ω indicates a short to ground or a short between circuit wires, preventing the Airbag Control Unit (ACU) from establishing a normal monitoring circuit. This safety-critical fault prevents the airbag from deploying during a collision, continuously illuminates the instrument panel SRS warning lamp, and may force the entire airbag system into fail-safe mode.B173BDTC B173B indicates an abnormal electric A/C compressor speed feedback signal or a communication fault between the compressor controller and the motor. In BYD new energy models (e.g., Tang, Song, Qin, and Yuan series), this DTC belongs to the HVAC subsystem within the Body Control system and specifically involves the electric compressor closed-loop control circuit. The ECU sets this DTC when the compressor controller (IPM) fails to receive a valid pulse signal from the Hall speed sensor for more than 3 continuous seconds, or when the deviation between the detected actual speed and the target commanded speed exceeds the calibrated threshold (typically >500 rpm). This fault forces the A/C system into fail-safe mode and stops compressor operation. Symptoms include a complete lack of cooling, intermittent cooling, or a sharp decrease in cooling performance. The instrument cluster A/C warning lamp may also illuminate. Prolonged operation with this fault can degrade high-voltage system insulation or cause controller overcurrent damage.
Common problems reported for Qin Plus →Qin Plus 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.