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B1640-00

This DTC indicates the Airbag Control Unit (ACU) detects an open circuit or abnormal resistance in the driver-side seat belt pretensioner circuit — Atto 3

Safety System

This DTC indicates the Airbag Control Unit (ACU) detects an open circuit or abnormal resistance in the driver-side seat belt pretensioner circuit.

The pretensioner contains a squib and a resistance wire; normal resistance typically measures 2.0-3.0Ω.

The ACU triggers B1640-00 when it detects infinite resistance (open circuit) in the pretensioner circuit or when the resistance remains outside the threshold range for a specified time.

During a collision, this fault may prevent the driver-side seat belt pretensioner from deploying and tightening, severely compromising occupant restraint protection.

The fault also forces the SRS system into a degraded protection mode and continuously illuminates the airbag warning light.

3
Cases Logged
Real-World Cases
BYD DTC AI AnalysisFrom Chinese market (translated)

Seat adjustment caused connector to loosen on Qin EV450

✓
A 2018 BYD Qin EV450 at 30,000 km came in with the SRS warning light on and DTC B1640-00 stored. The technician found that when the driver seat was moved fully rearward, a gap appeared between the yellow connector under the seat and the floor wiring harness. The connector lock was not fully engaged, causing an intermittent open circuit. Reseating the connector and securing the harness to the seat frame with cable ties to prevent it from moving with the seat fixed the fault. This issue is common in fleet vehicles where seats are frequently adjusted.
BYD DTC AI AnalysisFrom Chinese market (translated)

Qin 100 pretensioner internal open circuit fault

✓
2017 BYD Qin 100. After a low-speed collision, the SRS warning light stayed on with fault code B1640-00. Although the collision did not deploy the main airbag, inspection found infinite internal resistance in the driver's pretensioner. Disassembling the seatbelt retractor revealed the pretensioner squib had an internal open circuit due to a previous slight trigger (incomplete combustion). Replaced the driver's side seatbelt assembly, cleared fault codes with VDS, and the system passed the self-test. Fault resolved.
BYD DTC AI AnalysisFrom Chinese market (translated)

Wiring harness worn through at seat rail causing short circuit

✓
A Qin EV300 in commercial service logged an intermittent B1640-00 fault; the warning lamp occasionally went out on rough roads. The technician found the wiring harness inside the outer seat trim had been chafing against the metal seat rail, wearing through the insulation and causing an intermittent short to ground. The technician repaired the damaged harness (2 pretensioner wires), fitted abrasion-resistant corrugated tubing, and rerouted the harness to avoid interference with moving parts. This completely resolved the fault.
Other Atto 3 Fault Codes
P0A0DBattery Energy Control Module Requested MIL IlluminationP0AA6Hybrid Battery Voltage System Isolation FaultP1A00Drive Motor "A" Performance — BYD proprietaryB1108For 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.
Data confidence: Community This information is for reference only. Always consult a qualified technician for diagnosis and repair. Do not attempt high-voltage system repairs yourself.