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
5
Causes
Likely Causes — Seal U
  • 1Long-term vibration wears through the sensor wiring harness insulation where it passes through the instrument panel metal frame or firewall, causing the signal wire to short to body ground.
  • 2The thermistor package inside the cabin temperature sensor failed or absorbed moisture, causing an internal short circuit between terminals.
  • 3Poor drainage from the air conditioning evaporator housing causes water accumulation in the air duct; water ingress corrodes the sensor connector, shorting the pins to ground.
  • 4Missing wiring harness retaining clip after removing and refitting the centre control panel or instrument panel during repair, causing 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-side air duct or inside the centre console) causes a micro-short circuit.
What To Do
  • 1
    Connect the BYD VDS diagnostic tool and read the fault codes to confirm B2A2111 is a current active fault. Record the voltage value in the freeze frame data (usually 0.0V or close to 0V) and check for accompanying historical faults such as B2A2013 (open circuit).
  • 2
    Remove the centre control panel or passenger glovebox. Locate the in-cabin temperature sensor (on Song/Qin series, usually behind the air conditioning control module or inside the centre 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 is >10MΩ. If continuity exists, inspect the wiring route, focusing on the dashboard mounting bracket, firewall pass-through, and points where the harness contacts metal edges.
  • 5
    Check the 32-pin or 40-pin air conditioning controller connector (located behind the center control head unit or inside the passenger dashboard) and confirm there are no backed-out pins or corrosion. Measure the 5V reference voltage output at the controller terminal to verify it is normal.
  • 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 and secure the wiring harness to its original factory routing to prevent contact with sharp edges.
  • 7
    Reinstall all components, clear the fault code, start the vehicle, and set the A/C 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 vehicle 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 Seal U Fault Codes
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.B110A02DTC B110A02 indicates the thermal management master control unit (HVAC ECU) or body control module (BCM) failed to receive valid CAN data frames from the PM2.5 air quality sensor over consecutive communication cycles (typically 500ms per cycle). The sensor typically mounts at the HVAC unit air inlet or behind the glove box and transmits real-time particulate concentration data (unit: μg/m³) to the HVAC controller via the CAN bus. The fault is essentially a communication link layer timeout. Potential causes include physical layer wiring faults, sensor power supply failures, sensor internal MCU lockup, or CAN network topology damage. Although this non-critical fault does not directly affect driving safety, it disables the intelligent air purification strategy and the automatic fresh air/recirculation switching function. In extreme cases, it triggers a thermal management system degraded mode, limiting compressor power or fixing the air flap position.B110BDTC B110B indicates a fault in the internal air pump (sampling pump) of the PM2.5 air quality detector. This pump draws cabin or outside air into the PM2.5 sensor detection chamber, enabling the laser scattering sensor to measure real-time particulate matter concentration. The air conditioning controller (or BCM) sets this DTC upon detecting an open or short circuit in the pump drive circuit, or abnormal current caused by a seized pump motor. This fault disables the "Green Clean" system, causes the instrument cluster air quality display to read abnormally or disappear, and disables the automatic fresh air/recirculation switching function. It does not affect the vehicle powertrain or core thermal management functions.B173712DTC B173712 indicates a short to power in the firing circuit of the right second-row side airbag module in the Supplemental Restraint System (SRS). Specifically, the "right second-row side airbag" typically refers to the side impact airbag located in the right B-pillar or the side of the right seat. The "12" suffix indicates a circuit short to battery positive (B+). This fault causes the following conditions: 1) The airbag may fail to ignite and deploy during a collision, resulting in a loss of side impact protection. 2) In extreme cases, unintended triggering may cause accidental airbag deployment. 3) The SRS control unit detects abnormally high circuit voltage (typically above 4.5V) and enters fault protection mode. This may disable the entire airbag system and continuously illuminate the instrument cluster airbag warning light.
Common problems reported for Seal U →Seal U 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.