AU
B172312

DTC B172312 indicates the Supplemental Restraint System (SRS) detects an abnormally low-resistance path between the right knee airbag (Knee Airbag - Passenger Side) ignition circuit and the vehicle positive power supply (+B, usually 12V) — Seal U

Safety System

DTC B172312 indicates the Supplemental Restraint System (SRS) detects an abnormally low-resistance path between the right knee airbag (Knee Airbag - Passenger Side) ignition circuit and the vehicle positive power supply (+B, usually 12V).

In the SRS, normal airbag squib resistance is typically 2-3Ω.

The ECU supplies a low-voltage detection signal.

When the circuit shorts to power, the ECU detects an abnormally high voltage or a constant 12V and logs a Short to B+ fault.

This severe active safety system fault may cause: 1) the airbag to fail to deploy during a collision (the short circuit diverts ignition energy); 2) unexpected airbag deployment in extreme cases due to short-circuit current; 3) the SRS to enter fail-safe mode, restricting all airbag functions.

The '12' in the DTC is the sub-code specifically indicating a short-to-power fault.

4
Cases Logged
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Causes
Likely Causes — Seal U
  • 1Damaged right knee airbag wiring harness insulation contacts the instrument panel frame or power wiring harness (e.g., IGN+, constant power +B), causing a short circuit. Typically occurs after water ingress, underbody impact, or rodent damage.
  • 2Water ingress, corrosion, or bent pins in the right knee airbag connector (usually located under the right side of the dashboard, near the rear of the glove box), causing continuity between the power pin and the airbag igniter pin.
  • 3Squib insulation failure inside the knee airbag assembly causes an internal short circuit to power, usually due to airbag module aging or previous external impact.
  • 4SRS ECU (airbag control module) internal driver circuit fault, such as a MOSFET switch breakdown, causing abnormal energization of the ignition circuit.
  • 5During vehicle modifications (such as installing a dash cam or ambient lighting), mistakenly tapping the knee airbag wiring harness (wrapped in yellow corrugated conduit) for power, or a fixing screw piercing the harness and causing a short to power.
What To Do
  • 1
    Safety preparation: Switch the vehicle OFF, disconnect the low-voltage battery negative terminal, and wait at least 90 seconds to fully discharge the SRS capacitor and prevent accidental airbag deployment.
  • 2
    Fault confirmation: Use VDS or a BYD dedicated diagnostic tool to read the fault code. Confirm B172312 is a current fault (Active), not a historical fault. Record freeze frame data (ambient temperature, vehicle speed, etc.).
  • 3
    Visual inspection: Remove the lower right instrument panel cover (knee bolster). Check the right knee airbag wiring harness (yellow harness, usually two wires: high-side drive and low-side drive) for damage, pinching, water stains, or signs of unauthorized modification.
  • 4
    Circuit isolation: Disconnect the SRS ECU connector (located under the centre console or inside the armrest box) and the right knee airbag connector (usually a yellow 2-pin plug). Use a multimeter to check the airbag-side wiring harness for a short to power: measure the voltage between the harness terminal and body ground. The normal value is 0 V. A 12 V reading indicates a short to power in the circuit.
  • 5
    Section-by-section inspection: If the wiring harness shorts to power, open the corrugated conduit section by section along the routing (from the ECU to the airbag). Check for insulation wear, focusing on areas where the harness passes through instrument panel metal holes and retaining clips. Repair any damaged wiring and rewrap the harness.
  • 6
    Component test: If the wiring harness is normal, measure the knee airbag assembly resistance (via the connector or directly at the airbag plug). Normal resistance is 2.0-3.0Ω. If the resistance is abnormally low (<1Ω) or you measure voltage, replace the right knee airbag assembly.
  • 7
    ECU verification: If the wiring harness and airbag are normal, check the output voltage at the corresponding SRS ECU pin. If the ECU continuously outputs 12V to this circuit with the ignition switch in the ON position, this indicates an internal ECU fault. Replace the airbag control module.
  • 8
    System reset: After repair, reconnect all connectors and the battery negative terminal. Use a diagnostic tool to clear the fault code and perform an SRS self-check (typically, the warning light illuminates for 6 seconds after ignition ON, then turns off). Perform a comprehensive passive safety system test (e.g., use a dummy resistor to test the continuity of each airbag circuit). Finally, perform a road test to verify the repair.
Real-World Cases
BYD DTC AI Analysis

Knee airbag connector shorted on water-damaged vehicle

✓
Vehicle: 2019 Qin Pro DM. Customer reported the airbag warning light on the instrument panel stayed on. Diagnosis found active DTC B172312. History showed the vehicle had water ingress to floor level one month earlier. Removed and inspected the right knee airbag connector (behind the glovebox). Found obvious water stains and copper corrosion inside the connector, causing only 0.8 Ω resistance between the power pin and airbag signal pin. Repair: cleaned the connector terminals, applied conductive anti-corrosion compound, replaced the waterproof seal. Fault resolved.
BYD DTC AI Analysis

Wiring harness damaged after accident repair caused a short circuit

✓
Vehicle: 2020 E3. After right-front collision repairs, the airbag warning light illuminated. Inspection found the right knee airbag wiring harness had been crushed in the accident. The insulation was damaged and the repairer did not properly seal it, leaving exposed copper wires in contact with the dashboard metal bracket. While the bracket connects to chassis earth via screws, the damaged harness section also contacted a permanently live wire that had been incorrectly connected during a previous modification. Repair: Cut out the damaged section, soldered the wires, and sealed with heat-shrink tubing. Re-secured the harness routing away from sharp metal edges.
BYD DTC AI Analysis

Internal short circuit in knee airbag assembly

✓
Model: 2019 Qin EV. No collision history, but DTC B172312 appeared intermittently. With the airbag connector disconnected, the harness side showed no short circuit. However, resistance between the two terminals at the airbag assembly connector measured 0.5Ω and fluctuated. Diagnosis: insulation breakdown inside the airbag squib due to aging. Repair: Replaced the right knee airbag assembly (disconnect battery before work; reconfigure SRS ECU coding after replacement). The fault has not returned.
BYD DTC AI Analysis

Incorrectly wired aftermarket equipment damaged SRS wiring.

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Vehicle: 2018 Qin PRO petrol. Customer installed unauthorised ambient lighting. When tapping power, they mistakenly spliced into the yellow knee airbag harness, treating it as a constant 12V feed. This sent 12V directly into the SRS circuit. Diagnostic scanner showed DTC B172312 and multiple related faults. Action: Removed the unauthorised wiring. Repaired the damaged SRS harness using same-spec high-temperature wire; soldered joints and double-layer heat shrink insulation applied. Restored factory harness layout. Performed a full SRS system test.
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: Official This information is for reference only. Always consult a qualified technician for diagnosis and repair. Do not attempt high-voltage system repairs yourself.