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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 — Qin Plus

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 Qin Plus indicates a short circuit in the high-pressure side pressure sensor signal circuit for the chiller/battery cooler refrigerant system. Severity is high because lost pressure feedback can limit charging or power output and may risk compressor or pipe damage. Common causes include worn wiring insulation or moisture-damaged sensor electronics. Visit an authorised dealer for diagnosis and repair. Typical repair cost data is available from 4 recorded cases.
4
Cases Logged
5
Causes
Likely Causes — Qin Plus
  • 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 the inner side of the underbody shield).
  • 2Short circuit in the pressure sensor internal circuit board due to moisture (sensor seal failure allowing refrigerant or water vapor to enter).
  • 3Short circuit between connector terminals (water ingress into the connector after wading causes electrolytic corrosion of the terminals, shorting the signal wire to the ground wire or power wire)
  • 4Improper repair procedures damaged the wiring harness (sharp metal edges cut the harness during previous chassis or front compartment repairs, leaving the damage unrepaired).
  • 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 a dedicated diagnostic tool, read the fault code status and freeze frame data, confirm the pressure sensor voltage (short circuits typically read 0V or the 5V reference voltage), and 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 of the chassis battery pack). Measure the resistance on the sensor side. Normal resistance is 2kΩ-10kΩ (depending on the model). If the resistance is <100Ω, replace the sensor assembly.
  • 3
    If the sensor is normal, measure the wiring harness side: Turn the ignition 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/A/C 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). Visually inspect the wiring harness, focusing on wear points in the front compartment high-temperature zone, inside the underbody shield, and at the battery pack mounting brackets.
  • 5
    Check connector sealing: inspect terminals for back-out, burning, or green corrosion, and measure insulation resistance between terminals. If signs of water ingress exist, 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 model. Observe the data stream to verify it returns to normal (normal pressure varies with ambient temperature, typically 0.8-1.5MPa@25℃) to confirm the fault point.
  • 7
    After completing the repair, clear the fault code, calibrate the refrigerant pressure (if the repair manual requires it), and start the thermal management system self-test. 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

✓
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

✓
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

✓
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 Qin Plus 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.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.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.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.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 Qin Plus →Qin Plus 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.