AU
B178812

This DTC indicates a short to vehicle power positive (B+) in the driver-side front airbag Stage 2 inflator circuit — Atto 3

Safety System

This DTC indicates a short to vehicle power positive (B+) in the driver-side front airbag Stage 2 inflator circuit.

In modern dual-stage airbag systems, separate circuits control the Stage 1 and Stage 2 inflators, triggering them in stages based on collision severity (Stage 1 low power, Stage 2 high power).

A short to power means the airbag control unit (ACU) detects the Stage 2 inflator circuit voltage remaining abnormally high (12V).

This prevents this airbag stage from deploying correctly during a collision (because the power supply bypasses the trigger circuit) and creates a major safety hazard of unintended airbag deployment, as the short-circuit current can accidentally trigger the inflator.

The fault may originate in the clock spring, main wiring harness connector, airbag module, or the ACU.

The B178812 fault code on the Atto 3 indicates a short to vehicle power in the driver-side front airbag Stage 2 inflator circuit. This is a high-severity safety fault because it can stop correct airbag deployment or risk unintended deployment. Common causes include a damaged clock spring ribbon cable or chafed airbag wiring near the steering column. Visit an authorised dealer for diagnosis and repair. Typical repair cost data is available.
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Cases Logged
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Causes
Likely Causes — Atto 3
  • 1Damaged or broken insulation on the internal flat ribbon cable inside the steering wheel clock spring (spiral cable) shorts the stage 2 ignition wire to the power supply wire. As the most common cause, this frequently produces abnormal noise during steering wheel rotation or causes multifunction button failure.
  • 2Prolonged steering friction damages the airbag wiring harness outer sheath near the steering column, causing it to contact the body power wiring harness (e.g., ignition switch power wire) and create a short circuit.
  • 3During front-end accident repairs or interior trim removal/installation, an incorrectly installed airbag wiring harness connector, bent or deformed pins, or screws or cable ties crushing the harness insulation causes a short to power.
  • 4Airbag control unit (ACU) internal drive circuit fault (e.g., power transistor breakdown), causing the second-stage drive terminal to short internally to the positive power supply.
  • 5Flooding or deep interior cleaning causes water ingress and corrosion in the airbag wiring harness connector (located under the steering wheel or at the main airbag plug), creating a conductive path or verdigris that bridges the power terminals.
What To Do
  • 1
    Safety preparation: Set the vehicle to OFF. Disconnect the 12V low-voltage battery negative terminal and wait at least 3-5 minutes (allow the SRS backup capacitor to discharge completely). Wear an anti-static wrist strap. Do not use radio equipment near the airbag assembly.
  • 2
    Freeze frame analysis: Connect the VDS or X431 diagnostic tool to read DTC freeze frame data. Record vehicle speed, timestamp, and associated DTCs at the time of the fault. Check for accompanying B1788 (Level 1) or other SRS faults.
  • 3
    Visual inspection: Inspect the clock spring connector under the steering wheel and the main airbag connector (yellow plug) for obvious signs of burning, melting, water ingress, or backed-out pins. Check if the airbag wiring harness retaining clip has detached, causing the harness to hang unsupported.
  • 4
    Section-by-section measurement: Disconnect the connector below the clock spring. Use a multimeter to measure the resistance between the second-stage ignition wire and the positive power supply (normal: infinity/OL). If continuity exists, continue isolating the circuit to determine if the fault is in the clock spring, body wiring harness, or airbag module.
  • 5
    Component replacement test: If measurements show an internal short circuit in the clock spring, replace the clock spring. If the airbag module has an internal short to power (continuity exists between the second-stage pin of the airbag connector and the housing or power terminal), replace the driver airbag assembly.
  • 6
    Wiring harness repair: If the body wiring harness is damaged, wrap it with two layers of high-temperature insulating tape (neoprene or fiberglass). Avoid ordinary PVC tape (melts at high temperatures). Re-secure the wiring harness to prevent further wear.
  • 7
    Verification test: Restore all connections and turn on the power. Use the diagnostic tool to clear the fault code and perform the SRS system self-diagnosis (Active Test). Confirm the B178812 status is 'Past' or cleared. Confirm the airbag warning lamp turns off normally after 6 seconds. Perform a road test to verify.
Real-World Cases
BYD DTC AI Analysis

2019 Qin EV clock spring internal short caused DTC B178812

✓
Airbag warning light stayed on when the vehicle arrived at the shop. Read DTC B178812. Found the code cleared with the steering wheel at full left lock, but returned when centered. Removed the steering wheel and found insulation damage between the stage 2 igniter circuit and power supply wiring inside the clock spring. Replaced the clock spring (part number: BYD-3773110). Fault resolved. Analysis: repeated steering wheel rotation over long-term use caused fatigue damage to the internal wiring.
BYD DTC AI Analysis

E2 ride-hail: Airbag false positive for short-to-power after accident repair

✓
An E2 rideshare vehicle was in a minor frontal collision. After an outside repair shop replaced the front bumper and airbag control unit (ACU), fault code B178812 set and would not clear. Inspection revealed the ACU-to-steering wheel harness retaining clip was missing where the harness passes through the firewall. The harness rubbed against the steering column bracket, wearing through the insulation until the copper core contacted the bracket (ground). The bracket had a high-resistance connection to battery positive through some path. Re-wrapping the harness and fitting a protective sleeve cleared the fault.
BYD DTC AI Analysis

E3: Corroded airbag connectors in flood-damaged vehicle

✓
2020 E3 fault code B178812 appeared one month after flood damage repairs. Found green copper corrosion inside the driver airbag connector (yellow). Electrolyte had formed a conductive path between the second stage ignition terminal and the adjacent power terminal (typically for the horn or multifunction buttons). Cleaned the connector and treated with electronic contact restorer. Insulation resistance returned to normal. Recommend replacing the waterproof airbag connector seal to prevent further water ingress.
BYD DTC AI Analysis

Steering wheel modification damaged the secondary ignition line

✓
A 2019 Qin EV owner fitted a racing steering wheel then reverted to stock, triggering DTC B178812. Inspection revealed that forcible deformation of the shorting bar on the second stage airbag igniter line during disassembly had shifted the pin within the connector into contact with the power pin. Additionally, an incorrect pinout on the aftermarket clock spring used for the modification allowed 12V to enter the airbag circuit. Replacing the clock spring with a genuine unit and repairing the pins resolved the issue.
Other Atto 3 Fault Codes
P0AA6Hybrid Battery Voltage System Isolation FaultB1108For 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.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.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.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.
Common problems reported for Atto 3 →Atto 3 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.