AU
B1770

This DTC indicates the SRS control module detects an abnormal 0 Ω resistance in the right rear seat belt pretensioner circuit — Atto 8

Safety System

This DTC indicates the SRS control module detects an abnormal 0 Ω resistance in the right rear seat belt pretensioner circuit.

As a pyrotechnic device, normal pretensioner resistance ranges from 1.5 to 3.0 Ω.

A 0 Ω reading typically indicates a short circuit.

Possible causes include damaged wiring harness insulation shorting the positive and negative terminals, an internal connector short, a shorted internal resistance wire within the pretensioner body, or an SRS ECU internal drive circuit fault.

This fault prevents the pretensioner from deploying during a collision.

The SRS system may also disable airbag functions in the affected area, posing a severe safety hazard.

4
Cases Logged
5
Causes
Likely Causes — Atto 8
  • 1Harness wear short circuit: Long-term bending and friction damaged the wiring harness insulation inside the right rear B-pillar or sill panel, shorting the positive and negative wires.
  • 2Connector water ingress and corrosion: Poor sealing of the right rear seat belt pretensioner connector (usually located under the seat or at the base of the B-pillar) allows water ingress, causing a short circuit between pins.
  • 3Pretensioner unit fault: Internal resistance wire short circuit (rare but possible, usually resulting from a manufacturing defect or overcurrent)
  • 4Improper repair work: previous seat or interior trim panel removal/installation crushed the wiring harness or a screw pierced the harness, causing a short circuit.
  • 5SRS ECU internal fault: Short circuit in the control module internal drive circuit falsely reports pretensioner resistance as 0 (rule out via cross-checking).
What To Do
  • 1
    Safety preparation: Disconnect the 12V battery negative terminal and wait at least 90 seconds to fully discharge the SRS capacitor and prevent accidental airbag deployment.
  • 2
    Visual inspection: Check the right rear seat belt pretensioner connector (located at the bottom of the B-pillar or on the outboard side of the seat) for water ingress, corrosion, deformed pins, or foreign matter.
  • 3
    Wiring harness inspection: Check the wiring harness along the B-pillar trim panel and door sill trim panel for wear, pinching, or damaged insulation. Pay special attention to the wiring harness near the seat slide rail.
  • 4
    Resistance measurement: Disconnect the pretensioner connector. Use a multimeter to measure the pretensioner body resistance (should be 1.5-3.0Ω). Measure the resistance to ground on the wiring harness side (should be infinite).
  • 5
    Short circuit location: After confirming a wiring short circuit, inspect the wiring harness in sections. If necessary, strip back the corrugated conduit to locate the short circuit point. Repair the insulation or replace the wiring harness.
  • 6
    Component replacement: If the pretensioner unit has a short circuit, replace the right rear seat belt assembly (including the pretensioner). Do not repair the pyrotechnic device separately.
  • 7
    Verification test: Restore connections, clear the fault code, perform an SRS system self-check, confirm B1770 does not return, and verify related functions operate normally.
Real-World Cases
BYD DTC AI Analysis

Tang DM right rear sill wiring harness worn through and shorted

✓
A 2021 Tang DM presented with DTC B1770. The technician removed the right rear sill trim and found the pretensioner wiring harness had chafed against the seat rail mounting bracket, wearing through the insulation and exposing the copper wires, which shorted. Repair: Wrapped the damaged area with insulation tape, rerouted the harness and added a protective sleeve. Fault resolved.
BYD DTC AI Analysis

Connector corrosion on Song MAX after water ingress

✓
A 2019 Song MAX logged DTC B1770 after wading through heavy floodwater. Found water in the right rear B-pillar base pretensioner connector; pins had oxidized and blackened, causing a short. Cleaned and dried the connector, but resistance remained below spec. Replaced the wiring harness connector and seal — fault resolved.
BYD DTC AI Analysis

Wiring harness pinched after seat removal on BYD Yuan EV

✓
A 2019 BYD Yuan EV developed this fault after seat cover replacement. The owner confirmed prior seat removal and reinstallation. Inspection found seat mounting bolts had crushed the pretensioner harness, causing a short. Repair: Replaced the damaged harness section, rerouted wiring to specification, and secured the harness clear of pinch points.
BYD DTC AI Analysis

Qin Pro pretensioner internal short circuit

✓
A 2020 BYD Qin Pro petrol variant logged DTC B1770. Disconnected the pretensioner connector and measured infinite resistance on the harness side (normal), but 0.2Ω across the pretensioner itself (near short). Replaced the right rear seatbelt assembly (includes pretensioner). Cleared the code—no recurrence.
Other Atto 8 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.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.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.B110AThis DTC indicates interrupted CAN bus communication or abnormal data between the air conditioning control unit (ACU) and the PM2.5 air quality sensor. The PM2.5 sensor monitors particulate concentration inside and outside the vehicle and provides the basis for purification control in the automatic air conditioning system. The ACU triggers this fault if it fails to receive a valid CAN message from the sensor within the specified period (usually 100-500 ms), if message verification fails, or if the signal frame times out. Although this fault does not affect vehicle driving safety, it disables the automatic air purification function. The air conditioning system cannot automatically switch between recirculation and fresh air modes or activate the air purification mode based on air quality. A persistent fault may restrict the thermal management strategy.
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.