AU
B2A5B13

DTC B2A5B13 indicates an open signal circuit in the Passenger Side Floor Vent Temperature Sensor — Atto 3

Thermal Management System

DTC B2A5B13 indicates an open signal circuit in the Passenger Side Floor Vent Temperature Sensor.

This sensor typically uses a Negative Temperature Coefficient (NTC) thermistor and mounts at the passenger-side air-conditioning duct outlet.

It monitors the footwell outlet air temperature in real time and provides closed-loop control feedback for the dual-zone or multi-zone automatic air-conditioning system.

When the ECU detects the sensor signal voltage continuously exceeding the calibrated threshold (typically corresponding to infinite resistance or >100kΩ), it sets an open circuit fault.

This fault prevents the air-conditioning controller from reading the actual passenger-side outlet air temperature and may trigger a fail-safe mode.

The system may disable the independent passenger-side temperature control, force a default temperature (e.g., 24℃), or operate solely based on the driver-side setting.

This severely impacts occupant comfort but does not directly affect the vehicle powertrain or safety systems.

5
Cases Logged
5
Causes
Likely Causes — Atto 3
  • 1Internal open circuit in the sensor body: NTC thermistor element aging, internal cold solder joints, or vibration-induced lead wire breakage, resulting in an infinite resistance reading at room temperature.
  • 2Wiring harness connector fault: Loose connection, backed-out pins, water ingress/oxidation, or poor contact at the mating connector between the front passenger side floor wiring harness and the body wiring harness (usually located under the front passenger seat or near the A-pillar).
  • 3Physical damage to the wiring harness: Long-term chafing causes broken copper wires where the internal instrument panel harness interferes with the moving air flap actuator, or where the floor harness rubs against the seat slide rails.
  • 4ECU detection circuit fault: Damaged sampling resistor or ADC channel in the air conditioning controller internal signal acquisition circuit (relatively rare).
  • 5Improper modification or repair: Fixing screws pierced the wiring harness during the installation of front passenger seat heating or floor sound insulation, or previous dashboard repairs failed to restore correct wiring harness routing.
What To Do
  • 1
    Fault Confirmation and Freeze Frame Analysis: Use VDS or X431 to read the DTC freeze frame. Record the ambient temperature, air outlet mode, and sensor voltage values when the fault occurred. Confirm whether the fault is continuous (current code) or intermittent (history code).
  • 2
    Visual and physical inspection: Check the front passenger footwell air duct temperature sensor connector (usually located on the right side or underneath the air duct) for looseness. Inspect the pins for green oxidation, backed-out terminals, or deformation. Check the floor wiring harness for pinch damage from the seat or signs of water ingress.
  • 3
    Sensor body resistance measurement: Disconnect the sensor connector. Use a multimeter to measure the resistance across the sensor terminals (standard value at 25°C is approximately 2.0–3.0 kΩ; resistance decreases as temperature increases). If the reading shows infinity (OL) or an extremely high value (>1 MΩ), replace the temperature sensor (part number HE-8116400 or similar).
  • 4
    Harness continuity and insulation test: Measure the harness resistance between the sensor connector and the corresponding A/C ECU pin (should be <1Ω). Inspect the mating connector between the floor harness and the body harness. Measure the signal wire insulation resistance to ground and to power to eliminate short circuits.
  • 5
    Reference voltage and signal verification: Turn the ignition switch to the ON position. Without disconnecting the connector, measure the sensor supply voltage (normal: 5V ± 0.25V). The signal wire voltage should vary between 0.5-4.5V with temperature. If the voltage is 5V (full reference voltage), confirm an open circuit.
  • 6
    Repair verification: After repairing or replacing the faulty component, clear the fault code. Start the air conditioning system, switch to 'footwell' mode, and adjust the temperature setting. Observe the data stream to verify the 'front passenger footwell temperature' value changes normally with the outlet air temperature. Perform a 10-minute road test to confirm the fault does not recur.
Real-World Cases
BYD DTC AI Analysis

Corroded front passenger floor wiring harness connector on BYD Song MAX caused intermittent open circuit

✓
2018 BYD Song MAX. Owner reported the passenger-side AC intermittently blew hot air and would not adjust. Scan tool retrieved B2A5B13 (current). Removed and inspected the floor-to-body harness connector beneath the passenger seat (white 6-pin). Found traces of water inside the connector and green corrosion on the pins, causing intermittent resistance on the temperature sensor signal line (resistance jumped between 2kΩ and infinity when wiggling the harness). Root cause: water entered the floor area during a previous car wash or when driving through deep water in the rain. Cleaned the pins with electronic contact cleaner, applied conductive grease, and wrapped the connector in heat-shrink tubing to waterproof it. Cleared the codes and test drove; live data showed the passenger footwell outlet temperature tracking normally with the setpoint. One month follow-up, no recurrence.
Original source ↗
BYD DTC AI Analysis

Qin PRO EV: Worn wiring harness inside dashboard caused sensor open circuit

✓
2019 Qin PRO EV, 30,000 km. Air conditioning panel displayed 'passenger temperature sensor fault'. Read DTC B2A5B13. Measured the sensor connector at the passenger footwell vent duct: 5V supply normal, but signal line showed infinite resistance to ground. Removed the passenger side lower dashboard trim panel and traced the wiring harness along the duct. Found the damper actuator linkage arm had worn through the insulation nearby; internal copper wires were completely broken, leaving only a few strands. The owner had previously had the cabin filter replaced at an external workshop and likely did not refit the harness retaining clips. Replaced the dashboard wiring harness assembly (Part No.: ED-5824500), secured the harness routing with cable ties ensuring 20 mm clearance from moving parts. Configured the new harness and cleared the fault.
Original source ↗
BYD DTC AI Analysis

BYD Song MAX: Temperature sensor connector left unplugged after accident repairs, causing open circuit

✓
A 2017 Song MAX showed 'Thermal Management System Fault' on the instrument cluster with no cold air after front collision repairs. The scan tool reported B2A5B13 and multiple communication DTCs. Inspection revealed the passenger airbag and dashboard had been removed and reinstalled. During reassembly, the 2-pin connector for the passenger footwell temperature sensor was left unplugged, hanging behind the air duct. Reconnecting it did not clear the codes. Sensor resistance measured infinite (open circuit), indicating internal damage from the impact. Replaced the passenger footwell temperature sensor (Part No.: SA-5982000), secured the connector, and wrapped it with tape to prevent loosening. Cleared the codes and ran 'HVAC System Self-Learning'. Verified all air door actuators positioned correctly. Road tested 20 km; the fault did not return.
Original source ↗
BYD DTC AI Analysis

Qin EV300 sensor body aged, internal open circuit

✓
2017 BYD Qin EV300, 5 years/80,000 km. Passenger-side AC temperature control failed. Historic DTC B2A5B13. Sensor resistance measured open at room temperature; internal NTC element failed open. Replaced sensor, fault resolved. Long-term use caused thermistor aging and fracture—normal end-of-life wear. Recommend regular cabin air filter replacement to reduce dust buildup in the ducts and prevent corrosion of the sensor thermistor.
BYD DTC AI Analysis

Seat modification crushed wiring harness on Qin PRO DM, causing intermittent fault

✓
2018 BYD Qin PRO DM. Owner installed an aftermarket passenger seat ventilation system; the AC subsequently developed intermittent faults. Inspection found the seat mounting bolts had crushed through the protective corrugated tubing of the floor wiring harness during the modification, fracturing the copper core of the temperature sensor signal wire. The damaged wire intermittently lost and regained contact when the vehicle hit bumps. Repaired the harness and re-routed it clear of the seat runners. Fault completely 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: Official This information is for reference only. Always consult a qualified technician for diagnosis and repair. Do not attempt high-voltage system repairs yourself.