AU
B174400

The BYD Qin PRO series defines DTC B174400 as "Crash Output Fault", a critical safety fault in the SRS airbag system — Qin Plus

Safety System

The BYD Qin PRO series defines DTC B174400 as "Crash Output Fault", a critical safety fault in the SRS airbag system.

This indicates the airbag control unit (ACU) detects a circuit abnormality when attempting to output a crash trigger signal to other vehicle systems.

In BYD new energy vehicles, this specifically refers to a crash signal interaction fault between the ACU, the high-voltage system manager (BMS/VCU), and the body control module (BCM), including: 1) A short to power/ground or an open circuit in the crash output signal line; 2) Damage to the ACU internal crash output driver MOSFET circuit; 3) Abnormal feedback signals from receiving actuators (e.g., high-voltage power cut-off relay, fuel pump cut-off relay, and door unlock relay).

During a collision, this fault prevents high-voltage system disconnection (electric shock risk), fuel pump shutoff (fire risk), and automatic door unlocking (hindering escape and rescue).

This significantly increases the risk of secondary accidents.

Hyundai/Kia vehicles typically define this DTC as "Front Passenger Side Pressure-Type Side Impact Sensor ID Error", indicating cross-brand definition differences.

For BYD systems, prioritize diagnosing the crash output signal circuit and ACU driver circuit faults.

The B174400 fault code on the Qin Plus indicates a crash output fault in the SRS airbag system. Severity is medium, but it can affect crash-related functions such as high-voltage cut-off or door unlocking. Common causes include a damaged ACU crash output driver or worn, shorted, or open crash signal wiring. The recommended fix is to visit an authorised BYD dealer for diagnosis and repair. Typical repair cost data is available.
3
Cases Logged
5
Causes
Likely Causes — Qin Plus
  • 1Damaged internal crash output driver circuit in the SRS control unit (ACU), or an outdated software version causing a false warning.
  • 2Collision output signal wiring harness (connected to high-voltage system manager, BCM, fuel pump relay, etc.) worn at door hinge, shorted to power/ground, or open circuit.
  • 3Internal short circuit at the high-voltage system manager or BCM crash signal input port, causing abnormal feedback voltage.
  • 4A previous vehicle collision damaged the ACU or related wiring harness resulting in incomplete repairs, or non-genuine parts caused a signal mismatch.
  • 5Right front door pressure-type side impact sensor (P-SIS) fault, poor connector contact, or lost ID registration causes the ACU to misjudge collision status.
What To Do
  • 1
    Use the BYD VDS2000 or the latest diagnostic tool to read all SRS fault codes and freeze frame data. Confirm whether B174400 is a current or historical fault code, and record key information such as vehicle speed and time of occurrence.
  • 2
    Visually inspect the front and sides of the vehicle for signs of collision. Check the SRS control unit (located under the center console or gear selector) for external damage, mounting security, and water ingress at the connector.
  • 3
    Measure the continuity of the crash output signal circuits (including the high-voltage interlock cut-off signal wire, fuel pump cut-off signal wire, and door unlock signal wire). Inspect the wiring harness at the right front door hinge for wear or damaged insulation, and measure for short circuits to power or ground.
  • 4
    Check the operating status and feedback circuit resistance of the relevant actuators (high-voltage power cut-off relay, fuel pump relay, central locking actuator). Confirm no short circuit exists at the receiving end (normal feedback resistance is typically 2-3kΩ).
  • 5
    If the wiring harness and actuator are normal, perform the ACU self-diagnostic test and check the software version. Update to the latest version if necessary. If the fault persists, replace the airbag control unit, complete online coding, and write the configuration parameters.
  • 6
    After repair, perform the collision output function test (use a diagnostic tool to simulate a collision signal) and verify functions such as high-voltage system power-off, fuel pump shut-off, and automatic door unlocking operate normally. Clear the fault code and perform a road test to verify.
Real-World Cases
BYD DTC AI Analysis

Qin Pro DM right front pressure sensor ID error caused abnormal collision output.

✓
The airbag warning light on the instrument cluster stayed on. The scan tool read DTC B174400. The right front door had recently received panel and paint repair. During disassembly, we found the pressure side impact sensor (P-SIS) connector was not fully seated, causing an intermittent connection. The ACU could not correctly identify the sensor ID, triggering the collision output fail-safe mode. We reseated the connector and replaced the pressure sensor. After performing the sensor ID registration with the scan tool, the fault cleared.
Original source ↗
BYD DTC AI Analysis

Qin Pro petrol version door wiring harness wear causes collision signal fault

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While driving, the airbag warning light suddenly illuminated, accompanied by intermittent central locking failure. Retrieved fault code B174400. Inspection found the wiring harness at the right front door hinge had suffered fatigue wear from long-term repeated door opening and closing. The pressure sensor communication lines (CAN-H/L) had fractured and were making poor contact, preventing the ACU from receiving correct side impact sensor data. Repaired the damaged wiring harness (re-soldered and wrapped with waterproof tape) and replaced the pressure sensor that may have been damaged by the wiring short circuit. Fault resolved.
BYD DTC AI Analysis

Qin Pro DM: ACU internal driver circuit fault after accident repair

✓
The vehicle sustained front-end collision damage. After the dealership replaced the airbags and sensors, the airbag warning light stayed on and DTC B174400 could not be cleared. Checked the signal wiring harness from the collision output to the high-voltage system manager—it was normal. The high-voltage manager receiving port was normal. Measured no voltage at the ACU output terminal. Determined the collision had damaged the collision output driver chip inside the ACU. Replaced the airbag control unit and completed online matching, coding, and high-voltage system integration. The warning light went out and the simulated collision test functioned normally.
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.