AU
B2A2111

In-Car Temperature Sensor signal circuit short to ground — Atto 3

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.

The B2A2111 fault code on the Atto 3 indicates the in-car temperature sensor signal circuit is shorted to ground. This is a high-severity HVAC fault that can disrupt automatic temperature control and cause abnormal heating or cooling. Common causes include damaged wiring insulation rubbing on body metal, or moisture/internal failure in the sensor. The recommended fix is to visit an authorised dealer for diagnosis and repair. Typical repair cost data is available.
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Cases Logged
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Causes
Likely Causes — Atto 3
  • 1Long-term vibration wears the sensor wiring harness insulation where it passes through the instrument panel metal frame or firewall, shorting the signal wire to body ground.
  • 2Failure or moisture ingress of the thermistor package inside the cabin temperature sensor body causes an internal short circuit between terminals.
  • 3Poor drainage from the air conditioning evaporator housing causes water to accumulate in the air duct. Water ingress corrodes the sensor connector, causing the pins to short to ground.
  • 4After removing and refitting the centre control panel or instrument panel during repair, a missing wiring harness retaining clip causes the wiring harness to contact a sharp-edged metal bracket.
  • 5After water ingress or flooding in the front compartment or passenger cabin, residual moisture in the sensor connector (usually located in the front passenger air duct or inside the centre console) causes a micro-short circuit.
What To Do
  • 1
    Connect the BYD VDS diagnostic tool, read the fault codes to confirm B2A2111 is a current active fault, record the voltage value in the freeze frame data (usually displaying 0.0V or close to 0V), and check for accompanying historical faults such as B2A2013 (open circuit).
  • 2
    Remove the center control panel or passenger-side glove box and locate the in-cabin temperature sensor (on Song/Qin series, this is usually located behind the air conditioning control module or inside the central air vent duct). Visually inspect the connector for oxidation, water stains, or backed-out terminals.
  • 3
    Disconnect the sensor connector and use a multimeter to measure the resistance between the two terminals on the sensor body. The standard value at 25°C ambient temperature is 1.5-2.5kΩ. If the resistance is <100Ω, the sensor has an internal short circuit. Replace the sensor assembly.
  • 4
    If the sensor is normal, measure the resistance between the harness-side signal wire (usually yellow/green or white) and body ground. Normal value: >10 MΩ. If continuity exists, trace the wiring route and inspect the dashboard mounting bracket, firewall pass-through, and harness-to-metal contact points.
  • 5
    Check the 32-pin or 40-pin air conditioning controller connector (located behind the central control head unit or inside the passenger side dashboard). Verify there are no backed-out pins or corrosion, and measure the 5V reference voltage output at the controller terminal to confirm normal operation.
  • 6
    Repair the damaged wiring harness: If only the insulation is damaged, wrap the wire with waterproof tape and protect it with corrugated conduit. If the copper wire is broken, solder the wire and seal it with heat-shrink tubing. Restore the wiring harness to its factory routing and secure it to prevent contact with sharp edges.
  • 7
    Reinstall all components, clear the fault code, start the vehicle, and set the air conditioning to AUTO mode. Observe the data stream to verify the 'interior temperature' value updates with ambient temperature changes (the variation range must match the actual temperature). Run the system for 10 minutes to confirm the fault code does not return.
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 Atto 3 Fault Codes
P0AA6Hybrid Battery Voltage System Isolation FaultB1108For 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.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.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.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.
Common problems reported for Atto 3 →Atto 3 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.