AU
B122013

This DTC indicates an open circuit in the thermal management system right heatsink temperature sensor (NTC thermistor) — Atto 8

Thermal Management System

This DTC indicates an open circuit in the thermal management system right heatsink temperature sensor (NTC thermistor).

In BYD Qin EV/DM models, this sensor typically mounts on the PTC heater heatsink or the motor controller (MCU) IGBT heatsink to monitor power device operating temperatures in real time.

When sensor wiring breaks, the sensor fails, or the connector makes poor contact, the control module detects a voltage signal outside the valid range (typically because the 5V reference voltage fails to complete a circuit) and logs this fault.

Because the system cannot accurately monitor the heatsink temperature, it triggers a thermal management protection strategy.

This strategy may disable the PTC heater or limit motor power output.

In extreme cases, power devices may overheat and fail, making this a severe fault.

4
Cases Logged
5
Causes
Likely Causes — Atto 8
  • 1Temperature sensor body aging or physical damage: The internal thermistor element has an open circuit. Resistance measures infinite at room temperature (normally approximately 10kΩ, varying with temperature).
  • 2Wiring harness worn or broken: High temperatures in the engine bay or front compartment degrade and crack the sensor wiring harness insulation, or vehicle vibration causes the harness to rub against sharp edges, breaking the copper wire.
  • 3Poor connector contact: loose sensor plug, backed-out terminals, oxidized or corroded pins, or incomplete connector seating during servicing causing an intermittent connection.
  • 4Water ingress corrosion: Water enters the sensor connector during front compartment cleaning or wading, causing the terminals to oxidize or short-circuit, then burn out and create an open circuit.
  • 5Control module sampling circuit fault (rare): Damage to the internal sampling resistor or reference voltage circuit in the air conditioning controller or thermal management module causes a false sensor open circuit detection.
What To Do
  • 1
    Diagnostic tool data stream analysis: Connect the VDS or dedicated diagnostic tool and read the 'right-side heat sink temperature' data stream. If the reading displays -40°C, 255°C, or remains fixed, confirm an abnormal signal. Simultaneously read the relevant PTC or MCU temperature data to determine if the fault involves the same component.
  • 2
    Sensor body inspection: Disconnect the sensor connector and measure the resistance between the two sensor terminals using a multimeter. The standard value at room temperature (25°C) is approximately 10 kΩ ±5%. If the resistance is infinite or deviates significantly from the temperature-resistance curve, replace the sensor.
  • 3
    Circuit continuity check: Leave the sensor disconnected and measure harness continuity from the control module end. Measure the harness resistance between the corresponding BMS or air conditioning controller pin and the sensor connector. Resistance must be less than 1 Ω. Check for shorts to ground and shorts to power to confirm only an open circuit exists, not a short circuit.
  • 4
    Connector check: Visually inspect the sensor plug and socket terminals for oxidation, burning, backed-out pins, or looseness. Test terminal retention force using a dedicated probe. Clean with electrical contact cleaner or replace the plug/socket if necessary.
  • 5
    Repair verification: After repairing or replacing the faulty component, clear the fault code. Start the vehicle and run the PTC heater or drive motor to heat the heat sink. Observe the data stream to verify the temperature value changes correspondingly, confirming the fault is resolved.
Real-World Cases
BYD DTC AI AnalysisFrom Chinese market (translated)

Qin EV300 PTC heater temperature sensor open circuit due to aging.

✓
A 2017 BYD Qin EV300 with 120,000 km on the clock displayed ‘Power System Fault’ on the instrument cluster and had no heating. Read DTC B122013. Live data showed right-side heat sink temperature at –40°C. Removed and inspected the PTC heater water outlet temperature sensor (right-side heat sink sensor); the connector was oxidised and the sensor measured infinite resistance. Replaced the sensor. The new sensor measured 10.2 kΩ at 22°C ambient. Reconnected the connector, live data returned to normal, and heating function restored.
BYD DTC AI AnalysisFrom Chinese market (translated)

Qin Pro DM: Front compartment wiring harness wear caused an intermittent open circuit.

✓
2018 Qin Pro DM. Intermittent DTC B122013 with no cabin heating when the fault occurred. Inspection found the fault only appeared over bumps. Traced the wiring harness from the PTC controller to the sensor and found it had worn through at the firewall clip from prolonged vibration, leaving only a few copper strands connected; the circuit broke completely on rough roads. Repaired the harness by cutting out the damaged section, soldering in an extension, and protecting it with high-temperature tape and corrugated conduit. Adjusted the routing to avoid contact with sharp edges. Fault resolved.
BYD DTC AI AnalysisFrom Chinese market (translated)

Sensor connector corroded from water ingress after wading.

✓
A 2019 Qin Pro DM lit the cooling system warning light the day after wading through deep floodwater. Pulling codes gave B122013. Inside the right-side radiator temperature sensor connector, I found water stains, green copper corrosion, and infinite resistance across the terminals. Water had wicked up the harness by capillary action during the water crossing, oxidizing the contacts and causing an open circuit. I replaced the sensor connector (with pigtail), dried the original harness and treated it with corrosion protection, applied conductive grease, and reconnected. Fault cleared.
BYD DTC AI AnalysisFrom Chinese market (translated)

Connector not reseated after repair caused false fault code

✓
After front collision repairs, the vehicle logged DTC B122013. Inspection found that after replacing the front compartment wiring harness, the technician had swapped the right-side radiator temperature sensor connector with a nearby two-pin connector (front compartment temperature sensor). They plugged in, but the mismatched pin configuration caused an open circuit. Correcting the connections cleared the fault code and restored normal operation. During repairs, pay attention to the error-proof design of similar connectors to prevent mix-ups.
Other Atto 8 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. Sources: [1]