AU
B164F

DTC B164F indicates the measured circuit resistance of the front passenger side (front right) seat belt pretensioner is 0 ohms — Atto 8

Safety System

DTC B164F indicates the measured circuit resistance of the front passenger side (front right) seat belt pretensioner is 0 ohms.

In BYD SRS (Supplemental Restraint System) circuit logic, a 0-ohm resistance typically indicates a short to ground or a low-impedance short, rather than an open circuit.

The pretensioner contains a squib and heating wire; normal resistance is 1.5-3.0 Ω.

This fault causes the SRS control module to register an abnormal pretensioner circuit, meaning the pretensioner may fail to tension the seat belt during a collision.

The instrument cluster AIRBAG/SRS warning light remains illuminated, the system enters fail-safe mode, and the SRS module may simultaneously disable the front airbags, severely compromising occupant protection.

3
Cases Logged
5
Causes
Likely Causes — Atto 8
  • 1Water ingress, oxidation, or bent metal terminals in the pretensioner wiring harness connector under the front passenger seat causing a short circuit between positive and negative terminals.
  • 2Insulation breakdown of the seat belt pretensioner internal heating wire causes an internal short circuit (squib fault).
  • 3Long-term friction from the seat rail adjustment mechanism damages the wiring harness insulation, causing the core wire to directly contact the vehicle body ground.
  • 4SRS control module (ACU) internal sampling circuit fault causing a false low resistance reading.
  • 5Using a multimeter on the resistance setting to directly measure the pretensioner connector during repair (violating safety procedures and causing static or current damage), or failing to fully lock the connector after seat removal and installation, causing the terminal to contact the metal bracket.
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: Remove the front passenger seat (or lift the front of the seat). Inspect the yellow pretensioner connector (usually located on the outer side or bottom of the seat) for looseness, water ingress, corrosion, or foreign objects causing terminal short circuits. Inspect the wiring harness at the seat slide rails for wear.
  • 3
    Disconnect the pretensioner: Carefully disconnect the pretensioner connector. Connect a dedicated airbag resistor substitute (2Ω) to the SRS module side harness. Power on and read the fault code. If the fault code becomes intermittent or disappears, the harness to the ACU has no short circuit; the fault is in the pretensioner body or connector.
  • 4
    Resistance measurement: Use a digital multimeter to measure the resistance between the two terminals of the pretensioner body. Normal value: 1.5-3.0Ω. Measure the resistance between either terminal and vehicle body ground; the value should be infinite (OL). If the body resistance is 0 or shows continuity to ground, replace the pretensioner assembly.
  • 5
    Harness continuity check: Disconnect both ends of the wire and test the pretensioner harness circuit for a short to ground. Inspect the insulation at the bent section under the seat.
  • 6
    Component replacement and verification: Replace the faulty pretensioner (use genuine parts; do not dismantle or repair). Reconnect all connectors, clear the DTC, and perform a full seat travel adjustment test. Confirm the SRS warning lamp turns off normally at IGN ON (turns off after the 6-second self-check).
Real-World Cases
BYD DTC AI AnalysisFrom Chinese market (translated)

Seat cleaning caused water ingress into the connector, resulting in a short circuit

✓
A 2020 BYD Qin Pro came in with the SRS light on. The diagnostic tool read fault code B164F (passenger pretensioner resistance 0). Inspection revealed the owner had recently had the interior deep-cleaned at a detailing shop, and cleaning fluid leaked into the passenger seat pretensioner connector (yellow double-lock connector) underneath. Opening the connector revealed severely oxidised terminals shorted together. Repair: cleaned the connector thoroughly with electronic contact cleaner, dried it with compressed air, applied conductive grease, reconnected and wrapped with waterproof tape. Cleared the fault code and the SRS light returned to normal. Follow-up after one week showed no recurrence.
BYD DTC AI AnalysisFrom Chinese market (translated)

Seat adjustment mechanism crushed wiring harness, causing intermittent short circuit.

✓
2019 BYD Yuan EV with intermittent SRS warning light and sporadic DTC B164F. Inspection found the power-adjustable passenger seat harness was interfering with the metal edge of the slide rail during forward and rearward movement. At a specific seat position (fully rearward), the harness insulation had worn through, allowing the internal copper wires to contact the seat frame and cause a short to ground. Repaired the damaged harness by re-wrapping with insulating tape and heat shrink tubing, adjusted the harness clip positions, added corrugated tubing protection, and ensured no interference throughout the full seat travel range.
BYD DTC AI AnalysisFrom Chinese market (translated)

Pretensioner internal squib short circuit — replace assembly

✓
A 2021 BYD Tang DM set DTC B164F after accident repairs (passenger seatbelt assembly replaced). Checked connectors and harness – found no faults. Disconnected the pretensioner plug and measured 0.2 Ω across the unit (near short circuit). Disassembled the old component and found the heating wire inside the pretensioner had deformed from incorrect assembly pressure, causing an inter-turn short. Repair: replaced the OEM front passenger seatbelt pretensioner assembly (includes retractor), performed SRS system configuration coding (some models require VDS to write the new part code), completed system self-test, and cleared the fault codes.
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. Sources: [1]