AU
B176C-00

This DTC indicates the airbag control unit (SRS ECU) detects the left rear seat belt pretensioner igniter resistance exceeds the calibrated threshold (normal range is typically 1 — Atto 8

Safety System

This DTC indicates the airbag control unit (SRS ECU) detects the left rear seat belt pretensioner igniter resistance exceeds the calibrated threshold (normal range is typically 1.6-2.4Ω; the DTC triggers when detected resistance is >3.0Ω or an open circuit occurs).

As a key actuator in the passive safety system, the pretensioner uses the igniter to detonate the gas generator during a collision, instantly tightening the seat belt to eliminate slack between the belt and the occupant.

Excessive resistance indicates high impedance or a potential open circuit in the igniter circuit.

This condition can prevent pretensioner deployment during a collision, severely compromising occupant restraint protection.

This is a hard DTC.

While the fault remains active, the system triggers a continuous warning and illuminates the airbag warning lamp.

Some models may also limit power output or disable specific assistance functions.

The B176C-00 fault code on the Atto 8 indicates excessive resistance or an open circuit in the left rear seat belt pretensioner igniter circuit. Severity is medium, as the pretensioner may not deploy correctly in a collision and the airbag warning lamp will stay on. Common causes include poor connector contact or damaged under-seat wiring. Visit an authorised dealer for diagnosis and repair. Typical repair cost data is available from recorded cases.
5
Cases Logged
5
Causes
Likely Causes — Atto 8
  • 1Poor pretensioner connector contact: Vibration, oxidation, or loosening increases contact resistance at the left rear pretensioner connector (usually located inside the C-pillar trim panel or under the seat). This is the most common cause of the fault, especially after wading or in damp environments.
  • 2Mechanical damage to the under-seat wiring harness: On foldable rear seats, frequent folding can break internal copper strands or damage insulation at the bend point of the pretensioner harness (usually yellow), causing high resistance or an intermittent open circuit.
  • 3Pretensioner unit aging: Oxidation of the igniter internal bridge wire or moisture ingress into the pyrotechnic charge causes resistance to drift beyond the normal range over time. This typically affects vehicles over 5 years old or those previously exposed to high-temperature, high-humidity environments.
  • 4Open circuit in SRS ECU to pretensioner wiring harness: Wear, rodent damage, or improper accident repairs partially break, but do not completely sever, the body wiring harness in the B-pillar or floor cable channel.
  • 5Airbag control unit internal fault: A fault in the SRS ECU internal sampling circuit or analog-to-digital converter causes a false high resistance reading. This is relatively unlikely. Rule out external wiring before confirming this fault.
What To Do
  • 1
    Safety preparation: Disconnect the 12V battery negative terminal and wait at least 90 seconds (or wait for the capacitors to fully discharge as required by the workshop manual). Ensure the SRS system is completely powered down to prevent accidental pretensioner deployment during inspection.
  • 2
    Locate the pretensioner: Remove the left rear seat and lower C-pillar trim panel. Find the left rear seat belt pretensioner assembly (usually integrated with the seat belt retractor) and identify the yellow dedicated wiring harness connector.
  • 3
    Visual inspection: Verify the pretensioner connector is fully seated and the locking tab is engaged. Inspect the connector pins for green oxidation, burning, or backed-out terminals. Check the wiring harness at the seat folding mechanism for signs of wear.
  • 4
    Resistance measurement: Measure the resistance across both pretensioner terminals using a dedicated SRS system diagnostic resistance meter (or a digital multimeter with current <1mA). Normal resistance is 1.6-2.4Ω. If resistance is >3.0Ω, disconnect the connector and measure the pretensioner body and wiring harness side separately. If the pretensioner body resistance is abnormal, replace the pretensioner. If the wiring harness side resistance is infinite, check circuit continuity.
  • 5
    Harness continuity test: Measure harness continuity from the SRS ECU connector to the pretensioner connector. Standard resistance must be <1 Ω. Measure insulation resistance to ground; it must be >1 MΩ. Inspect the harness bend points under the seat and the C-pillar pass-through hole.
  • 6
    Substitution check: Connect a 3Ω dedicated simulation resistor (or a known-good pretensioner) to the circuit. Clear the fault code and observe if it recurs to rule out a false ECU report.
  • 7
    Repair/Replace: Based on measurement results, repair the wiring harness (soldering + heat shrink tubing + corrugated conduit protection) or replace the pretensioner assembly. (Note: When replacing the pretensioner, record the old part number. After installing the new part, fully lock the connector and apply conductive grease to prevent oxidation.)
  • 8
    System reset: Reconnect all connectors and the battery. Use the diagnostic tool to clear the fault code. Perform the SRS system self-check. Verify B176C-00 does not return. Check that the airbag warning light turns off. Perform a final road test to verify.
Real-World Cases
BYD DTC AI Analysis

Wear on the left rear seat folding mechanism caused the wiring harness to break internally.

✓
A 2018 Qin EV450 had the airbag warning light permanently on. DTC B176C-00. Found the left rear seat had been frequently folded for carrying cargo. Removing the seat revealed the pre-tensioner harness at the folding hinge had intact insulation but 90% of the internal copper strands were fractured, leaving only minimal contact and causing resistance to read 4.2Ω. Fix: Cut out the damaged harness section. Reconnected with 0.5mm² high-temperature wire using soldered joints. Protected the repair with double-layer heat shrink tubing and corrugated conduit. Rerouted the harness to avoid interference with the folding mechanism. Fault cleared.
BYD DTC AI Analysis

C-pillar connector oxidation causing increased contact resistance

✓
2017 BYD Qin 80. Owner reported intermittent SRS warning light, occasionally clearing after bumps. Scan tool showed stored DTC B176C-00 with resistance at 2.8Ω (threshold). Removed and inspected the left rear C-pillar pretensioner connector; found green oxidation on the terminals and a loose lock. Cause: Previous water wading allowed moisture into the C-pillar connector. Fix: Cleaned the terminals with electrical contact cleaner, applied copper-powder conductive grease, and replaced the connector lock (or the complete connector). Resistance measured 1.9Ω after tightening. Fault has not returned.
BYD DTC AI Analysis

Pretensioner unit resistance drift due to aging

✓
2017 BYD Qin EV300, 6 years old. Airbag warning light stayed on with DTC B176C-00. Infinite resistance at the pre-tensioner connector; 5.6 Ω measured directly across the pre-tensioner terminals—well above spec. Disassembled the pre-tensioner: internal igniter bridge wire oxidised and fractured. Natural ageing of the pre-tensioner, related to coastal high-humidity conditions. Replaced the left rear seatbelt pre-tensioner assembly (part number matched to VIN). Resistance normal after replacement. Coded and configured with the diagnostic tool (some models require writing the new pre-tensioner serial number). Fault resolved.
BYD DTC AI Analysis

Wiring harness connector not fully locked after accident repair

✓
A Qin 100 involved in a left-rear collision set DTC B176C-00 one month after 4S repairs. Diagnosis showed the pretensioner had fired in the crash (but went unrecorded), or the shop had only replaced the seatbelt assembly without fully locking the connector. In reality, the technician seated the plug during repair but missed the audible click; vibration worked it loose, causing poor contact of approximately 3.5Ω. Re-plugging the connector until the locking tab fully engaged cleared the fault immediately. After any SRS repair, run a 'pull test' to verify the connector locks.
BYD DTC AI Analysis

SRS ECU internal sampling circuit false positive

✓
2018 Qin EV450 repeatedly set DTC B176C-00. Measured pretensioner and wiring harness resistance: 1.8Ω (within spec), continuity good, no oxidation. Replaced the left rear seat pretensioner and wiring harness; fault persisted, appearing randomly at power-on. Found slight water ingress on SRS ECU connector pins from a windscreen leak dripping onto the ECU. Dried the connector, sealed the leak (lower windscreen trim panel), and cleared the codes. Monitored for one week with no recurrence. Confirmed intermittent ECU detection circuit fault. If the fault recurs, replace the airbag control unit.
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.