AU
B17801B

DTC B17801B indicates the SRS (Supplemental Restraint System) control unit detects an open circuit in the right middle-row seat belt pretensioner circuit (resistance exceeds the normal range, typically >10Ω or infinite) — Atto 8

Safety System

DTC B17801B indicates the SRS (Supplemental Restraint System) control unit detects an open circuit in the right middle-row seat belt pretensioner circuit (resistance exceeds the normal range, typically >10Ω or infinite).

This fault essentially constitutes a 'passenger restraint system communication loss'.

During a collision, the pretensioner for this seat cannot receive the ignition signal and fails to retract the seat belt at the moment of impact to eliminate slack between the occupant and the belt.

This fault triggers the SRS downgrade protection strategy, potentially altering the airbag deployment logic for this seat and surrounding areas (such as delayed deployment or non-deployment), severely compromising passive safety performance.

For BYD E2/E3/Qin EV models, the right middle row typically refers to the second-row right seat.

The pretensioner integrates into the seat belt retractor and communicates with the SRS ECU via a dedicated yellow connector under the seat.

The B17801B fault code on the Atto 8 indicates an open circuit in the right middle-row seat belt pretensioner circuit, which can stop the belt from tightening correctly in a crash. Severity is medium because it may affect SRS protection and airbag logic. Common causes include a loose or corroded yellow SRS connector under the seat or a broken harness near the seat rail. Visit an authorised dealer for diagnosis and repair. Typical repair cost data is available.
5
Cases Logged
5
Causes
Likely Causes — Atto 8
  • 1Loose pretensioner wiring harness connector or oxidized contacts: Vehicle vibration, water ingress, or previous repairs loosen the yellow plug under the seat (usually marked 'SRS' or 'AIRBAG'), or terminal oxidation causes excessive resistance.
  • 2Wiring harness fatigue fracture at seat slide rail: On models with a sliding right middle-row seat, fore-aft seat adjustment repeatedly bends the pretensioner wiring harness, breaking the internal copper strands while leaving the outer insulation visually intact (hidden open circuit).
  • 3Pretensioner internal igniter circuit open: The internal pyrotechnic igniter or motor-driven pretensioner coil has an open circuit measuring infinite resistance. Pretensioner aging, moisture ingress, or failure to replace the pretensioner after deployment typically causes this fault.
  • 4Improper repair after a vehicle accident: A collision caused the pretensioner to deploy and retract, but during repair, the technician replaced only the seat belt assembly without replacing the pretensioner, or failed to clear the fault code after replacement.
  • 5Seat modification or non-standard parts: Removing but failing to reconnect the pretensioner during non-OEM seat installation or leather reupholstery, or installing an aftermarket seat without a pretensioner.
What To Do
  • 1
    Safety preparation: Turn off the ignition switch, disconnect the low-voltage battery (12V) negative terminal, and wait at least 90 seconds to ensure the SRS capacitor fully discharges. For new energy vehicles, first disconnect the high-voltage service disconnect and confirm the high-voltage system powers down.
  • 2
    Locate the component: Find the right middle-row seat belt pretensioner, usually at the outer base of the seat or below the B-pillar (varies slightly by model). Identify the dedicated yellow connector (with shorting bar protection).
  • 3
    Visual inspection: Verify the connector is fully seated and the shorting bar is not stuck. Inspect the wiring harness at the seat slide rail for wear or crush marks, and check for foreign objects under the seat obstructing the wiring harness.
  • 4
    Resistance measurement: Measure the resistance between the pretensioner connector terminals using a digital multimeter (must have a low-current test function, <10mA). The normal value is 2.0-3.0Ω (refer to the specific vehicle repair manual). Infinite resistance or >10Ω indicates an open circuit in the pretensioner body or wiring.
  • 5
    Harness continuity test: Disconnect the SRS ECU connector (disconnect the battery first). Measure the harness continuity between the pretensioner connector and the SRS ECU. Check for an open circuit or short to ground.
  • 6
    Repair action: If the connector is loose, reconnect and secure it; if the wiring harness is broken, repair or replace the harness (use high-temperature shielded wire); if the pretensioner itself is faulty, replace the seat belt assembly (the pretensioner is usually not available separately).
  • 7
    System reset: Reconnect all connectors and the battery negative terminal. Use VDS2000 or the BYD dedicated diagnostic tool to clear the fault code. Perform the "SRS system self-check" or "configuration check". Confirm B17801B does not return and the SRS warning light turns off.
Real-World Cases
BYD DTC AI Analysis

Wear on the right second-row seat rail severed the pretensioner wiring harness on the E3 ride-hailing vehicle.

✓
A BYD E3 rideshare vehicle with 120,000 km came in with the SRS warning light constantly illuminated. Scanned and retrieved DTC B17801B. Inspection revealed frequent seat sliding adjustments during commercial operation had chafed the wiring harness sheath at the right middle seat runner. Two internal conductors had completely fractured, though externally only minor scratches were visible. Repair: Cut out the damaged section, resoldered using 0.5 mm² high-temperature-resistant wire, insulated with double-layer heat-shrink tubing, and adjusted the harness routing to increase slack and prevent future chafing. Fault resolved.
BYD DTC AI Analysis

Qin EV pretensioner connector not plugged in after accident repair

✓
2019 BYD Qin EV. After a right rear collision, a non-authorised garage replaced the right rear door and seat. The owner noticed the SRS warning light on. Diagnosis revealed the right rear seat pre-tensioner connector was completely unplugged (technician likely forgot to reconnect it). Reconnected the yellow connector, confirmed the locking tab engaged, cleared the fault codes, and the system returned to normal. After accident repairs, check all SRS component connections.
BYD DTC AI Analysis

E2: Aftermarket seat replacement resulted in missing pretensioners

✓
The BYD E2 owner replaced the right-hand second-row seat assembly with an aftermarket unit after the original seat was damaged. After the replacement, the instrument cluster displayed an SRS warning. Inspection revealed the aftermarket seat lacked a seatbelt pretensioner and the connector hung loose. Solution: Installed an OEM seat assembly with the pretensioner, reconnected the wiring and configured the seat presence sensor parameters. DTC B17801B cleared.
BYD DTC AI Analysis

Pretensioner internal igniter open circuit due to aging

✓
An E3 parked for several days threw a B17801B immediately after startup. Connectors checked good and harness continuity was normal, but the pretensioner body measured infinite resistance. Disassembly found oxidized, fractured igniter terminals inside (likely from long-term humidity). Replaced the seatbelt pretensioner assembly (requires replacing the retractor as well). Fault cleared.
BYD DTC AI Analysis

SRS control unit software false positive (intermittent fault)

✓
Qin EV owner reported the SRS warning light comes on intermittently. Historical DTC B17801B present; current status shows historical fault. Checked wiring and resistance—normal. Suspected outdated SRS ECU software causing overly sensitive resistance threshold detection. Solution: Upgraded SRS control unit software to V2.1 or higher and cleared adaptive learning values. No recurrence after one month of monitoring.
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.