AU
B177511

DTC B177511 indicates a short to ground in the right rear (RR) seat belt pretensioner ignition circuit — Atto 8

Safety System

DTC B177511 indicates a short to ground in the right rear (RR) seat belt pretensioner ignition circuit.

In the BYD SRS (Supplemental Restraint System) architecture, the airbag control unit (ACU) sets this DTC when it detects the right rear seat belt pretensioner drive circuit resistance falls below the threshold (typically <1.0Ω, normal range 2.0-3.0Ω) or detects an abnormal drop in the circuit insulation resistance to body ground.

A short to ground prevents normal pretensioner deployment (failing to ignite the gas generator to tighten the seat belt during a collision).

Simultaneously, the ACU illuminates the airbag fault warning lamp and may disable the entire side or rear SRS protection strategy, severely compromising occupant passive safety.

This is a hard fault; once confirmed, it remains active and does not self-recover.

The B177511 fault code on the Atto 8 indicates a high-severity short to ground in the right rear seat belt pretensioner ignition circuit. This can stop the pretensioner from working in a crash and may trigger the airbag warning light. Common causes include an internally shorted pretensioner or damaged wiring near the B-pillar or seat area. Visit an authorised dealer for diagnosis and repair. Typical repair cost data is available.
5
Cases Logged
5
Causes
Likely Causes — Atto 8
  • 1Right rear seat belt pretensioner assembly internal short circuit: Moisture, aging, or manufacturing defects damage the pretensioner squib insulation, causing the ignition wire to short to the metal housing.
  • 2Mechanical wear of the B-pillar or seat wiring harness: Long-term bending and compression of the seat belt pretensioner wiring harness at the seat height adjustment mechanism, B-pillar trim panel, or slide rail damages the insulation layer, causing the copper core to contact the vehicle body metal frame.
  • 3Connector water ingress and corrosion: A poorly sealed pretensioner connector (usually a multi-pin black plug) located under the seat or at the base of the B-pillar allows water entry if the rear floor floods during wading or vehicle washing, causing a short circuit between terminals or to ground.
  • 4SRS control module (ACU) internal driver circuit fault: The pretensioner driver chip (MOSFET or dedicated ignition IC) breaks down and short-circuits, causing continuous conduction to ground. This fault usually triggers multiple pretensioner fault codes.
  • 5Improper after-sales repair: During accident repair or seat removal/installation, failing to secure the pretensioner wiring harness with standard clips causes interference with sharp metal edges; or installing a non-genuine seat belt assembly results in an impedance mismatch.
What To Do
  • 1
    Safety preparation: Disconnect the 12V battery negative terminal. Wait at least 90 seconds for the SRS capacitor to discharge fully to prevent accidental airbag deployment. Wear an anti-static wrist strap and disable the vehicle smart key system.
  • 2
    Initial visual inspection: Remove the right rear seat and lower B-pillar trim panel. Check the seat belt pretensioner wiring harness (usually wrapped in yellow corrugated conduit) for obvious damage, crushing, or burn marks. Check connector BG08 (or corresponding model pins) for water ingress, corrosion, or looseness.
  • 3
    Resistance isolation test: Disconnect the connector between the ACU and the pretensioner. Use a digital multimeter to measure the resistance between the two terminals on the pretensioner side (normal: 2.0-3.0 Ω), then measure the resistance from each terminal to body ground (normal: >1 MΩ). If the resistance to ground is <5 Ω, confirm a short to ground.
  • 4
    Sectional fault isolation: If the pretensioner unit resistance is normal, check the wiring harness. Set a multimeter to continuity and measure the intermediate harness connectors (such as the adapter plug under the seat) section by section. Determine whether the short circuit is at the pretensioner end, the middle harness section, or the ACU end.
  • 5
    Repair or replace: If the wiring harness is damaged, cut out the damaged section, solder an extension using high-temperature wire (≥150°C), insulate with double-layer heat-shrink tubing, and re-secure to the original factory wire clips. If the pretensioner shorts internally, replace the entire right rear seat belt assembly (do not replace the igniter separately). Verify the new part number matches the vehicle configuration.
  • 6
    System verification: Reconnect all connectors. Power on the vehicle. Use a dedicated diagnostic tool (VDS2000 or Launch X431) to clear the fault code. Perform "SRS system self-check" and "pretensioner resistance learning" (if supported). Verify the B177511 status is "Pass/History". Road test the vehicle and verify the airbag warning light is off.
Real-World Cases
BYD DTC AI Analysis

BYD Song PLUS DM-i: Right rear seatbelt pretensioner wiring harness chafed on slide rail causing short circuit

✓
Symptoms: Airbag warning light stayed on after starting. Scanner showed DTC B177511 (right rear seatbelt pretensioner short to earth); code would not clear. Diagnosis: Found under the seat that frequent seat adjustments by rear passengers had left the seatbelt pretensioner harness at the rear of the slide rail unsecured by the retaining clips. Long-term back-and-forth friction wore through the corrugated tubing, exposing the yellow power wire's copper strands which contacted the seat frame. Resistance to earth: 0.3Ω. Resolution: Repaired the harness (cut out the worn section, soldered in an extension, sealed with double-layer heat shrink), replaced three OEM harness retaining clips, and secured the harness to maintain >15 mm clearance from the frame throughout the full seat travel. Fault code cleared and SRS self-test passed after repair.
Original source ↗
BYD DTC AI Analysis

BYD Han EV B-pillar pretensioner connector corroded due to water ingress

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Symptoms: After rain or washing, the instrument cluster showed an intermittent airbag warning light. Scanned B177511 (intermittent fault). Diagnosis: Removed the right rear lower B-pillar trim. Found the pretensioner connector (at the base of the B-pillar near the carpet) seal perished. Terminal surfaces had green copper corrosion. Measured resistance from the connector terminals to body ground fluctuating between 0.5Ω and 50Ω with humidity. Resolution: Cleaned the connector terminals with electrical contact cleaner. Replaced the waterproof seal. Applied conductive anti-corrosion paste. Wrapped the harness for waterproofing using PVC tape and heat-shrink tubing. Rerouted the harness to avoid low spots where water pools. Fault resolved.
Original source ↗
BYD DTC AI Analysis

BYD Tang DM SRS control module internal drive circuit shorted

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Symptoms: After replacing the right rear seatbelt following a collision, DTC B177511 persisted along with B177311 (left rear seatbelt pretensioner short to ground). Diagnosis: Disconnected all rear pretensioner connectors and measured >10MΩ to ground on the harness side (normal). Reconnecting the ACU connector revealed continuity to ground at the pretensioner terminals, indicating an internal ACU fault. Disassembling the ACU showed the pretensioner drive MOSFET (BTS5045) had shorted due to collision impact. Fix: Replaced the airbag control module (ACU). Used VDS to code and configure the module (writing the vehicle VIN and configuration codes), performed sensor calibration and pretensioner resistance learning, and cleared the fault codes.
Original source ↗
BYD DTC AI Analysis

BYD Qin Pro DM: Pretensioner circuit short blew the fuse

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Symptom: Dashboard displayed SRS fault. Retrieved DTCs B177511 and B177612 (pretensioner short to power). Found fuse SCU15 (SRS power) under the dashboard blown; it blew immediately upon replacement. Diagnosis: Found the right rear seatbelt pretensioner harness pinched at the seat mounting bolt. Both positive and negative wires had chafed through and contacted the body, creating shorts to ground and power. Resolution: Repaired the damaged harness (replaced the complete section from ACU to pretensioner), rerouted the wiring to clear the seat mounting points, and secured it with OEM cable clips. Replaced the SRS fuse and cleared the fault codes; system now normal.
Original source ↗
BYD DTC AI Analysis

BYD Seal: Short circuit between pretensioner and seat occupancy sensor wiring harnesses

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Symptoms: Airbag warning light illuminated after OTA update. Retrieved DTCs B177511 and U017787 (lost communication with right rear seat occupancy detection module). Diagnosis: Found the pretensioner harness and seat occupancy pressure sensor harness crushed and damaged where they cross inside the seat foam. The pretensioner firing line (high current) shorted to the sensor signal line, causing the ACU to misinterpret this as a short to ground and protectively shut down the circuit. Fix: Separated the two harnesses and repaired the damaged sections (resoldered the pretensioner harness with high-temperature silicone wire; used shielded cable for the sensor harness). Added a thermal insulation spacer at the crossing point. Recalibrated the seat occupancy sensor. Fault cleared.
Original source ↗
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.