AU
B2A2311

DTC B2A2311 indicates a short to ground or short to power in the Ambient Temperature Sensor (ATS) signal circuit — Seal U

Thermal Management System

DTC B2A2311 indicates a short to ground or short to power in the Ambient Temperature Sensor (ATS) signal circuit.

This causes the air conditioning controller (ACECU) or thermal management controller (TMCU) to detect a voltage signal outside the normal range (typically 0.1-4.9V).

The sensor is an NTC thermistor with a normal resistance of approximately 2.3-2.5 kΩ at 25°C.

A short circuit causes the ECU to continuously receive an abnormally high or low temperature signal (depending on the short type).

This triggers automatic air conditioning system protection, prevents compressor startup, limits PTC heater power, and affects the battery thermal management system cooling or heating strategy.

Extreme cases may trigger high-voltage interlock protection and limit overall vehicle power output.

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Cases Logged
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Causes
Likely Causes — Seal U
  • 1Internal short circuit in the sensor body: Sensor seal failure allows rainwater or car wash fluid to enter, shorting the internal thermistor to the housing, or sensor aging causes abnormal resistance characteristics.
  • 2Damaged harness insulation: Front bumper collisions, chassis bottoming out, or loose harness retaining clips cause the harness to rub against body metal edges, shorting the signal wire to ground.
  • 3Connector water ingress and corrosion: The sensor is located under the front grille or bumper. When driving through water, connector seal aging and failure causes a short circuit between terminals or a short to ground.
  • 4Internal controller circuit fault: Breakdown of the sampling resistor or filter capacitor in the internal signal acquisition circuit of the air conditioning controller or thermal management controller causes a short circuit between the sensor power supply terminal and the signal terminal.
  • 5Improper repair: During previous front bumper or headlamp repairs, incorrect routing allowed a metal bracket to pinch the wiring harness, damaging the insulation and causing a short circuit.
What To Do
  • 1
    Diagnostic scan: Use VDS or ED400 to read fault codes. Confirm B2A2311 is a current fault (Active). Record the ambient temperature value in the freeze frame data. Check for related fault codes (such as B2A2213, U0146, etc.).
  • 2
    Visual inspection: Open the hood and check the ambient temperature sensor installation position (usually located in the center or left side of the front bumper air intake grille). Inspect the sensor housing for damage or cracks, and inspect the wiring harness for obvious wear or crush marks.
  • 3
    Circuit measurement: Disconnect the sensor connector. Measure the sensor body resistance (2.0-3.0 kΩ at 25°C; resistance decreases as temperature increases). Measure the resistance to ground at the harness-side signal terminal (must be >1 MΩ; a reading near 0 Ω indicates a short to ground). Measure the signal terminal for a short to power (must not measure 12 V).
  • 4
    Harness continuity check: Trace the harness from the sensor connector to the air conditioning controller (usually located behind the dashboard or near the front compartment power distribution box). Inspect the harness insulation at wear-prone points such as the front bumper mounting bracket and headlamp bracket.
  • 5
    Substitution check: Replace the ambient temperature sensor with a known-good sensor. Clear the fault code, then drive the vehicle or leave it stationary and observe. If the fault code does not return, the sensor is faulty. If the fault persists, focus inspection on the wiring harness and controller.
  • 6
    Repair and verification: Repair the damaged wiring harness (wrap with heat-shrink tubing or waterproof tape; replace the wiring harness assembly if necessary), seat the connector sealing ring correctly, clear the fault code, and verify the deviation between the sensor data stream and the actual ambient temperature is within ±2°C across the -20°C to 50°C range.
Real-World Cases
BYD DTC AI Analysis

Song MAX front bumper lower wiring harness worn through, shorted

✓
A 2018 Song MAX DM with 32,000 km displayed "Thermal Management System Fault" on the instrument cluster; the air conditioner was not cooling. VDS scanning revealed DTC B2A2311. Inspection found the wiring harness clip beneath the front bumper had detached, allowing the harness to rub against a metal bracket. The abrasion wore through the signal wire insulation, exposing the copper and causing a short to ground. Re-wrapped the damaged harness, fitted abrasion-resistant corrugated tubing, adjusted the harness routing and replaced the retaining clip to clear the fault.
BYD DTC AI Analysis

Qin Pro EV sensor seal failed, water ingress caused short circuit

✓
2019 Qin Pro EV. Air conditioning failed to start after driving through water. Retrieved DTC B2A2311. Removed the ambient temperature sensor from the centre of the front grille; the housing sealant had degraded and cracked. Water ingress caused the thermistor to short to the housing, measuring 0.5 Ω (abnormal). Replaced the sensor with an OEM ambient temperature sensor and applied waterproof silicone grease to the connector. Fault resolved.
BYD DTC AI Analysis

Incorrect wiring harness routing after accident repair caused intermittent short circuit

✓
2017 BYD Qin EV300. One month after front collision repairs, the vehicle intermittently displayed a 'motor overheat warning' and set DTC B2A2311. The front bumper wiring harness had been routed incorrectly during the repair, with the headlamp mounting bracket pinching the cable. Driving over bumps caused intermittent shorts to ground. Technicians re-routed the harness, replaced the damaged section, and torqued the bracket to the workshop manual specification. The fault has not recurred.
BYD DTC AI Analysis

Internal sampling circuit fault in the air conditioning controller

✓
2019 Song MAX. DTC B2A2311 set after cabin filter replacement. Checked the sensor and wiring harness – both normal. Further inspection found abnormally low resistance between the sensor signal pin and ground pin in the 32-pin connector at the AC controller (located behind the glove box). Disassembled the controller; internal sampling resistor shorted. Replaced the AC controller assembly and coded it. DTC cleared, temperature display normal.
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.