AU
B178E-00

This DTC indicates the airbag control unit (SRS ECU) detects a short to vehicle power (12V/B+) in the front passenger airbag Stage 2 inflator circuit — Qin Plus

Safety System

This DTC indicates the airbag control unit (SRS ECU) detects a short to vehicle power (12V/B+) in the front passenger airbag Stage 2 inflator circuit.

Dual-stage airbags feature two independent inflators for different crash severities: Stage 1 provides cushioning in minor collisions, and Stage 2 provides additional protection in severe collisions.

A short to power indicates an abnormal electrical connection between the inflator wiring and the battery positive terminal.

This fault causes the SRS system to enter fail-safe mode, illuminates the airbag warning light, and disables the front passenger airbag Stage 2 deployment function.

In extreme cases, it causes unintended airbag deployment or prevents normal deployment during a collision, creating a severe safety risk.

The B178E-00 fault code on the Qin Plus indicates a high-severity short to vehicle power in the front passenger airbag Stage 2 inflator circuit. This can disable part of the passenger airbag system, trigger the airbag warning light, and create a serious safety risk. Common causes include damaged clock spring wiring or damaged harness insulation near the airbag or SRS ECU. Visit an authorised dealer for diagnosis and repair. Typical repair cost data is available.
5
Cases Logged
5
Causes
Likely Causes — Qin Plus
  • 1Damaged internal wire insulation in the airbag clock spring (spiral cable/clock spring) shorts the stage 2 squib circuit to the power supply line.
  • 2Damaged wiring harness insulation between the front passenger airbag module and the SRS ECU, contacting the vehicle body metal frame or power supply wiring.
  • 3Retaining screws pinched or chafed the instrument panel internal wiring harness during removal and installation, causing a power short circuit.
  • 4SRS ECU internal driver integrated circuit (ASIC) fault causing an internal short to power at the squib output terminal.
  • 5Water ingress, corrosion, or bent pins in the front passenger airbag connector (yellow connector) causing a short circuit between the power terminal and the squib terminal.
What To Do
  • 1
    Safety preparation: Turn off the vehicle, disconnect the 12V battery negative terminal, and wait at least 90 seconds to fully discharge the SRS backup power supply and prevent accidental airbag deployment.
  • 2
    Fault confirmation: Connect the VDS or dedicated diagnostic tool, read the complete fault codes and freeze frame data, confirm B178E-00 is a current fault (not a history fault), and record the environmental data at the time of the fault.
  • 3
    Visual inspection: Check the front passenger airbag area, instrument panel, and center console for signs of impact, modifications, or non-original equipment. Inspect the yellow SRS wiring harness specifically for damage, crushing, or burn marks.
  • 4
    Connector inspection: Disconnect the front passenger airbag module connector (usually located behind the airbag or under the dashboard) and the clock spring connector. Inspect the terminals for corrosion, water ingress, burn marks, or abnormal pin contact.
  • 5
    Circuit continuity test: Use a multimeter to measure the resistance from the second-stage igniter terminal on the airbag harness side to body ground and to the power supply. The normal reading is an open circuit (infinite resistance). Continuity or an abnormal resistance value indicates a short circuit.
  • 6
    Clock spring test: Measure the continuity of the second-stage squib circuit between the inner and outer rings of the clock spring (spiral cable). Turn the steering wheel to the left and right lock positions. If the resistance changes or a short circuit occurs, replace the clock spring.
  • 7
    Insulation resistance measurement: Use a megohmmeter to measure the insulation resistance between the Stage 2 igniter circuit and the power supply. The standard value must be greater than 10MΩ. If the value is lower, inspect the wiring harness for damage.
  • 8
    Component Replacement: If the wiring harness is normal, perform a substitution test using a known-good airbag module. If the fault clears, replace the airbag module. If the fault remains, check or replace the SRS ECU.
  • 9
    System reset: After completing the repair, reconnect all connectors and restore battery power. Use the diagnostic tool to clear the fault code and perform an SRS system self-check. Confirm B178E-00 does not return and the warning lamp is off.
  • 10
    Function check: Read the crash sensor and airbag circuit resistance values. Verify the second-stage squib circuit resistance is within the specified range (usually 1.5-3.0Ω) with no short or open circuits.
Real-World Cases
BYD DTC AI Analysis

Clock spring internal short caused intermittent fault

✓
A 2018 BYD Qin EV450 intermittently illuminated the airbag warning light on the instrument cluster. DTC B178E-00 was retrieved. The fault appeared randomly, increasing in frequency when turning the steering wheel. The technician disconnected the airbag module and measured the harness from the clock spring to the SRS ECU, finding a short to power. Disassembling the clock spring revealed that at full steering lock, the second-stage igniter line in the internal flat cable was contacting the power supply line. After replacing the clock spring, the technician tested steering at full lock left and right; no recurrence.
BYD DTC AI Analysis

Dashboard modification pinched wiring harness, causing short circuit

✓
2017 BYD Qin 100. Owner reported constant airbag warning light, DTC B178E-00. Vehicle recently had a large centre console screen installed at an aftermarket shop. Technician found passenger-side dashboard bracket mounting screws were too long, piercing the SRS wiring harness sheath and causing a short between the second-stage igniter power and signal lines. Repaired harness damage (rewrapped with insulation), replaced damaged harness section, adjusted screw length. Cleared the fault. Advised owner to use professional repair shops for dashboard disassembly and reassembly.
BYD DTC AI Analysis

Connector corrosion and short circuit after water ingress

✓
A Qin EV300's airbag warning light illuminated after driving through deep flood water. Code B178E-00 stored and would not clear. Checked the passenger airbag connector (behind the glovebox) and found water staining and copper corrosion inside; degraded insulation between the terminals caused a short to power. Cleaned the connector with electronic contact cleaner, dried it with compressed air, and applied conductive anti-corrosion grease. Insulation resistance returned to normal. Cleared the code and the system returned to normal. Recommend checking the vehicle's water ingress sealing.
BYD DTC AI Analysis

SRS ECU internal driver chip failure

✓
2017 BYD Qin 80, no accident history. SRS warning light suddenly illuminated. Scan tool retrieved DTC B178E-00. Measured passenger airbag second stage igniter circuit to ECU — no external short. Disconnected ECU connector and measured harness side — normal. Reconnected ECU and fault returned. Disassembled SRS ECU and found internal igniter driver ASIC chip burnt out, causing internal short to power at second stage igniter output. Replaced SRS ECU, programmed and matched — fault resolved. Old ECU failed due to internal component ageing.
BYD DTC AI Analysis

Internal squib short circuit in airbag module

✓
During routine maintenance at a 4S dealership, a technician noticed the airbag warning light on in a Qin EV450 and retrieved DTC B178E-00. Measuring at the passenger airbag module connector revealed the second stage squib was shorted between both pins and to power. They disconnected the module and checked the squib pins on the module side: 0.5Ω with continuity to the housing, confirming an internal short in the second stage squib to the housing (ground/power reference). They replaced the passenger airbag assembly (including the module). The new module measured 2.1Ω and showed no continuity to the housing. Installation 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.