UAE
AU
B2A2111

In-Car Temperature Sensor signal circuit short to ground — Seal U

Thermal Management System

In-Car Temperature Sensor signal circuit short to ground.

This sensor typically mounts near the center instrument panel air vent or inside the HVAC duct and uses a Negative Temperature Coefficient (NTC) thermistor.

Normal operating voltage ranges from 0.5-4.5V (varying with temperature).

When the HVAC ECU detects the sensor signal line voltage remaining below 0.5V for longer than the set time threshold (typically 2-5 seconds), it determines a short to ground.

This fault causes the air conditioning system to lose the cabin ambient temperature feedback signal, resulting in automatic temperature control failure, disrupted compressor start-stop logic, and abnormal outlet air temperature (continuous maximum cooling or heating).

The fault may also affect the battery thermal management system comfort control strategy and, in severe cases, trigger Level 3 fault protection to limit air conditioning power.

4
Cases Logged
Real-World Cases
BYD DTC AI Analysis

2018 Song MAX: Air conditioning inoperative after dashboard removal and refitting

✓
Had a navigation system installed at an out-of-town aftermarket shop. The dashboard wasn't fully reassembled. While driving, the climate panel displayed "Please check A/C system" and VDS logged code B2A2111. Inspection found the installer had pinched the sensor wiring harness between the dashboard metal bracket and plastic trim. The insulation chafed through, causing the signal wire to short to ground. Repaired the damaged harness section, rerouted the wiring and fitted rubber grommets. Fault resolved.
BYD DTC AI Analysis

Qin EV300 abnormal temperature display after water wading

✓
After driving through approximately 30cm of water, the air conditioning auto mode failed and constantly blew hot air. The diagnostic tool showed active fault code B2A2111. Inspection found water beneath the cabin carpet. The cabin temperature sensor connector at the bottom of the centre dashboard air duct had water inside; electrolytic corrosion between the pins caused a short to ground. Drained the connector, cleaned it with precision electrical contact cleaner, and blow-dried it. Insulation resistance measured normal and the fault cleared. Also check the evaporator drain hose for blockages.
BYD DTC AI Analysis

Qin Pro DM sensor internal short due to aging

✓
Vehicle is four years old. Recently the AC cooling has been intermittent, with the dash occasionally displaying a thermal management fault. VDS detected B2A2111 intermittently. Removed the sensor and measured resistance: at room temperature it read only 50Ω and was unstable (normal is approximately 2kΩ), indicating the internal thermistor package had failed short. Replaced the genuine cabin temperature sensor (part number: EQ-8127000 or model-specific equivalent), cleared the fault code, and AC temperature control accuracy returned to normal.
BYD DTC AI Analysis

2019 Song MAX: Missing wiring harness retaining clips caused wear

✓
When driving on rough roads, the air conditioning system triggered intermittent warnings; no warnings appeared when stationary. Investigation revealed the sensor wiring harness retaining clip fractured where it passes through the passenger side dashboard frame. The harness moved within the aperture, causing the insulation to chafe against sharp metal edges and wear through, creating an intermittent short to ground. Repaired the damaged harness section and re-secured it with cable ties and foam tape to eliminate contact with metal components. Fault has not recurred.
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: Community This information is for reference only. Always consult a qualified technician for diagnosis and repair. Do not attempt high-voltage system repairs yourself.