AU
B2A1212

This DTC indicates the Thermal Management Control Unit (TMS) or air conditioning control module detects a short circuit in the signal circuit of the high-pressure side pressure sensor for the plate heat exchanger (Chiller/battery cooler) refrigerant circuit — Seal 6 EV

Thermal Management System

This DTC indicates the Thermal Management Control Unit (TMS) or air conditioning control module detects a short circuit in the signal circuit of the high-pressure side pressure sensor for the plate heat exchanger (Chiller/battery cooler) refrigerant circuit.

The sensor outputs an abnormal voltage (near 0 V when shorted to ground, or near 5 V or 12 V when shorted to power), exceeding the normal 0.5–4.5 V signal range.

This piezoresistive sensor monitors real-time refrigerant circuit pressure (typically 0–3.5 MPa) to control the Electronic Expansion Valve (EXV) opening and regulate compressor speed.

The short circuit eliminates system pressure feedback and prevents accurate refrigerant flow control.

This fault can trigger thermal management derating: limiting battery fast-charging power, prohibiting high-power discharge, and reducing motor power output.

In extreme cases, the loss of overpressure protection can cause pipe rupture or compressor damage.

The B2A1212 fault code on the Seal 6 EV indicates a high-severity short circuit in the high-pressure sensor signal circuit for the chiller/battery cooler refrigerant system. This can stop accurate pressure feedback and reduce charging, discharge, or motor power. Common causes include damaged wiring insulation or moisture inside the pressure sensor. Visit an authorised dealer for diagnosis and repair. Typical repair cost data is available from recorded cases.
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Cases Logged
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Causes
Likely Causes — Seal 6 EV
  • 1Wiring harness insulation wear causes the signal wire to short to ground (commonly at the front compartment firewall pass-through, harness clip wear points around the battery pack, or inside the underbody shield).
  • 2Short circuit on the pressure sensor internal circuit board due to moisture (sensor seal failure allows refrigerant or water vapor to enter).
  • 3Short circuit between connector terminals (water ingress into the connector after wading causes terminal electrolytic corrosion, shorting the signal wire to the ground wire or power wire)
  • 4Improper repair procedures damaged the wiring harness (a sharp metal edge cut the wiring harness during previous repairs to chassis or front compartment components, leaving the damage unaddressed).
  • 5Short circuit in thermal management control unit internal signal processing circuit (fault in ECU internal A/D conversion circuit or signal conditioning circuit; relatively rare)
What To Do
  • 1
    Connect the VDS or dedicated diagnostic tool. Read the fault code status and freeze frame data. Verify the pressure sensor voltage (a short circuit typically reads 0V or the 5V reference voltage). Record the ambient temperature and system status at the time of the fault.
  • 2
    Disconnect the refrigerant pressure sensor connector near the plate heat exchanger (usually on the right side of the front compartment or the front end of the chassis battery pack). Measure the resistance on the sensor side. Normal resistance is 2kΩ-10kΩ (depending on the specific model). If resistance is <100Ω, replace the sensor assembly.
  • 3
    If the sensor is normal, measure the wiring harness side: Set the ignition to ON and measure the voltage between the signal wire and ground. If 0V, check for a short to ground; if 5V/12V, check for a short to power. Disconnect the TMS/air conditioning controller connector and measure the insulation resistance of the signal wire to ground and to power. The resistance must be >10MΩ.
  • 4
    Perform a wiring harness continuity test: Measure continuity between the sensor connector signal terminal and the corresponding TMS pin (normal: <1Ω). Inspect the wiring harness for visible damage, focusing on wear points in the front compartment high-temperature area, inside the underbody shield, and at the battery pack mounting bracket.
  • 5
    Check connector sealing: inspect terminals for backing out, burn marks, or green corrosion. Measure insulation resistance between terminals. If the connector shows signs of water ingress, clean and dry the connector. Replace the sealing ring or wiring harness assembly if necessary.
  • 6
    Jumper verification: Perform a substitution test using a known good sensor of the same type. Observe if the data stream returns to normal (normal pressure varies with ambient temperature, typically 0.8-1.5MPa@25℃) to confirm the fault location.
  • 7
    After repair, clear the fault code. Perform refrigerant pressure calibration (if required by the workshop manual). Start the thermal management system self-test and verify the deviation between the actual pressure and the sensor feedback value is within ±0.05MPa. Road test the vehicle to verify normal battery cooling/heating function.
Real-World Cases
BYD DTC AI Analysis

Qin EV plate heat exchanger pressure sensor shorted after water ingress

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After driving through water, the dashboard reported a thermal management system fault. Retrieved DTC B2A1212. Found water inside the refrigerant pressure sensor connector at the front of the underfloor battery pack. Electrolytic corrosion between terminals had shorted the signal wire to ground. Disassembled the connector and found green copper corrosion. Wiring harness continuity tested normal. Cleaned the terminals thoroughly, dried with compressed air, applied electronic contact protectant, and replaced the seal ring. Fault cleared. Check underbody shield sealing to avoid driving through water again.
BYD DTC AI Analysis

Wiring harness wear caused intermittent short circuit

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2019 BYD Qin EV intermittent thermal management fault while driving, DTC B2A1212 intermittent. Found wiring harness sheath damaged where it routes from the front bulkhead to the chassis. On rough roads, the signal wire intermittently shorted to chassis ground. Insulation resistance normal at rest but dropped sharply when shaking the harness. Repaired the damaged harness, re-wrapped with abrasion-resistant corrugated tubing, and adjusted retaining clip positions to avoid sharp edges. Fault completely resolved.
BYD DTC AI Analysis

Internal short circuit in the sensor

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AC not cooling; thermal management warning light on. Scanner read B2A1212. Disconnected the sensor connector: harness side voltage normal (4.8V on signal wire), but resistance across the sensor pins measured only 15Ω—shorted. Removed the sensor and found the internal circuit board shorted from long-term corrosion due to refrigerant micro-leakage. Replaced the refrigerant pressure sensor, recovered and recharged the refrigerant, ran a system pressure test (hold test), and delivered after confirming no leaks.
BYD DTC AI Analysis

Improper wiring harness routing after repair caused short circuit

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The vehicle presented with fault code B2A1212 following a battery pack replacement at a non-authorised repairer. Inspection revealed the technician had pinched the refrigerant pressure sensor wiring harness between the battery pack mounting bracket and the body. Prolonged compression damaged the insulation and caused a short to ground. Re-routed the harness to avoid the pinch point and secured it with genuine retaining clips. Repaired the damaged conductors using solder and heat-shrink tubing. Restored standard routing and cleared the fault.
Other Seal 6 EV 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.B1737DTC B1737 indicates the Supplemental Restraint System (SRS) detected abnormal continuity between the right middle-row side airbag squib circuit (typically the second-row right seat side airbag or right curtain airbag) and the vehicle power supply (B+, battery positive). The SRS ECU monitors the airbag inflator resistance via an internal current source (normal resistance: 2.0–3.0 Ω). If the ECU detects the voltage across the inflator circuit remaining close to battery voltage (>5 V and approaching 12 V) instead of the expected low potential or floating state, it identifies a short to power. This fault prevents the airbag from deploying normally during a collision because the short circuit bypasses the firing current. In extreme cases, abnormal current can cause unintended deployment, posing a severe safety hazard.B173BDTC B173B indicates an abnormal electric A/C compressor speed feedback signal or a communication fault between the compressor controller and the motor. In BYD new energy models (e.g., Tang, Song, Qin, and Yuan series), this DTC belongs to the HVAC subsystem within the Body Control system and specifically involves the electric compressor closed-loop control circuit. The ECU sets this DTC when the compressor controller (IPM) fails to receive a valid pulse signal from the Hall speed sensor for more than 3 continuous seconds, or when the deviation between the detected actual speed and the target commanded speed exceeds the calibrated threshold (typically >500 rpm). This fault forces the A/C system into fail-safe mode and stops compressor operation. Symptoms include a complete lack of cooling, intermittent cooling, or a sharp decrease in cooling performance. The instrument cluster A/C warning lamp may also illuminate. Prolonged operation with this fault can degrade high-voltage system insulation or cause controller overcurrent damage.
Common problems reported for Seal 6 EV →Seal 6 EV 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.