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) — Atto 8

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.

The B172312 fault code on the Atto 8 indicates a high-severity SRS fault where the right knee passenger airbag ignition circuit is shorted to battery power. This can stop the airbag working correctly or, in rare cases, cause unintended deployment. Common causes include damaged wiring insulation, water ingress, corrosion, or bent connector pins near the glove box. 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 — Atto 8
  • 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. Commonly occurs after water ingress, underbody impact, or rodent chewing.
  • 2Water ingress, corrosion, or bent pins in the right knee airbag connector (typically located under the right side of the dashboard, near the rear of the glove box) causing continuity between the power supply pin and the airbag igniter pin.
  • 3Insulation failure of the internal squib in the knee airbag assembly causes an internal short to power, usually due to airbag module aging or previous external impact.
  • 4Internal driver circuit fault in the SRS ECU (airbag control module), such as a MOSFET switch breakdown, causing abnormal energization of the ignition circuit.
  • 5Mistakenly stripping the knee airbag wiring harness (wrapped in yellow corrugated tubing) to tap power during vehicle modifications (such as installing a dash cam or ambient lighting), or a mounting screw piercing the harness and causing a short to power.
What To Do
  • 1
    Safety preparation: Set the vehicle to 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 (Active) fault, not a historical fault. Record freeze frame data (ambient temperature, vehicle speed, etc.).
  • 3
    Visual inspection: Remove the lower right instrument panel trim (knee bolster) and inspect the right knee airbag wiring harness (yellow harness, typically 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 center 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 0V; a 12V reading indicates a short to power in the circuit.
  • 5
    Section-by-section inspection: If the wiring harness shorts to power, strip back the corrugated conduit section by section along the routing (from the ECU to the airbag). Inspect for insulation wear, focusing on areas where the harness passes through metal holes in the instrument panel and at retaining clips. Repair 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 detect 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, confirm an internal ECU fault and replace the airbag control module.
  • 8
    System reset: After completing the repair, reconnect all connectors and the battery negative terminal. Use the diagnostic tool to clear the fault code. Perform an SRS system self-check (normally, the indicator light illuminates for 6 seconds after ignition ON and 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 for verification.
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.

✓
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 Atto 8 Fault Codes
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.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.B110B07This fault code indicates abnormal operation of the internal air pump (sampling pump) in the PM2.5 air quality detection module. The PM2.5 detector uses the laser scattering principle to measure particulate concentration and requires a built-in air pump to draw ambient air into the detection chamber at a constant flow rate. The ECU sets this code when it detects an open or short in the air pump drive circuit, abnormal current (stall or free-running), or abnormal speed feedback. This fault causes the automatic air conditioning system to lose air quality sensing capability, preventing automatic switching between fresh air and recirculation modes. The instrument cluster air quality display may show '--' or a fixed value, but the fault does not affect the vehicle powertrain or basic air conditioning cooling and heating functions.B173CDTC B173C indicates the Supplemental Restraint System (SRS) detects the Right Second Row Side Airbag squib circuit resistance exceeds the calibrated threshold (typically >4.5Ω). This fault is an active diagnostic result of the SRS system, indicating a high-resistance condition in the circuit between the Airbag Control Unit (ACU) and the airbag module. Causes for excessive resistance include increased contact resistance, a partially broken wiring harness, terminal oxidation, or an aging squib wire inside the airbag module. This fault causes the system to mark the airbag circuit as 'unreliable', meaning the airbag may fail to deploy during a collision. The fault typically illuminates the instrument cluster airbag warning light (SRS light) continuously, and some models also sound a warning buzzer.
Common problems reported for Atto 8 →Atto 8 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.