AU
B1650

DTC B1650 indicates the SRS (Supplemental Restraint System) control module detects the front passenger-side seat belt pretensioner igniter circuit resistance is below the calibrated threshold (typically <1 — Atto 8

Safety System

DTC B1650 indicates the SRS (Supplemental Restraint System) control module detects the front passenger-side seat belt pretensioner igniter circuit resistance is below the calibrated threshold (typically <1.0 Ω; normal range: 2.0-3.0 Ω).

This indicates a potential short circuit in the internal pretensioner bridge wire, or a short to ground or wire-to-wire short in the harness.

This fault prevents the SRS from triggering the front passenger seat belt pretensioner during a collision (loss of pretensioning protection), or creates a risk of unintended deployment in extreme cases.

The system illuminates the airbag warning lamp and may disable the front passenger airbag deployment function.

In some BYD model years, this code may also indicate an Occupant Classification System (OCS) communication fault.

However, based on the provided fault context, prioritize checking the pretensioner assembly and its wiring harness resistance.

4
Cases Logged
5
Causes
Likely Causes — Atto 8
  • 1Seat belt pretensioner internal squib short circuit (internal bridge wire broken and shorted to ground, or manufacturing defect causing excessively low resistance)
  • 2Chafed wiring harness insulation under the seat or inside the B-pillar trim panel causes the power wire to short to body ground.
  • 3Pretensioner connector (yellow waterproof plug, usually located under the seat or at the base of the B-pillar): water ingress, oxidation, or bent or deformed pins causing a short circuit between pins.
  • 4Vehicle wading, damp socket after deep interior cleaning, or electrical leakage due to prolonged exposure to a damp environment.
  • 5SRS control module internal sampling circuit fault or calibration data loss, causing incorrect resistance measurement.
What To Do
  • 1
    Safe power-down: Turn off the ignition switch, disconnect the negative battery terminal, and wait at least 90 seconds to fully discharge the SRS capacitor and prevent accidental airbag deployment.
  • 2
    Locate component: Remove the front passenger lower B-pillar trim and seat side trim, then locate the seat belt pretensioner yellow connector (usually integrated into the bottom of the seat belt retractor or below the B-pillar).
  • 3
    Visual inspection: Check the connector for looseness, water ingress, white oxidation marks, or bent pins; check the wiring harness near the seat rail for secure mounting, wear, or crush marks.
  • 4
    Resistance measurement: Measure the resistance at the pretensioner connector using a dedicated low-current multimeter (or dedicated airbag system tester). Normal resistance is 2.0-3.0Ω. A reading <1.0Ω indicates a short circuit. Never measure directly using a standard multimeter resistance setting (excessive current may deploy the pretensioner).
  • 5
    Harness isolation test: Disconnect the pretensioner connector. Measure the harness-side resistance to ground (should be infinite) and the resistance between harness wires (should be infinite) to determine if the short circuit is in the harness or the pretensioner itself.
  • 6
    Replacement verification: If testing confirms a short circuit in the pretensioner body (internal fault), replace the front passenger seat belt pretensioner assembly. If the wiring harness is faulty, repair the damaged section (solder and insulate with double-layer heat shrink tubing).
  • 7
    System reset and verification: Restore all connections and turn on the power. Clear the fault code using the BYD VDS or a dedicated diagnostic tool. Perform the SRS system self-check cycle (cycle the ignition switch ON-OFF three times). Confirm the warning light turns off and B1650 does not return. Perform a road test to verify.
Real-World Cases
BYD DTC AI AnalysisFrom Chinese market (translated)

BYD Song Plus DM-i B1650 Fault After Wading Through Water

✓
After driving through water, the SRS warning light remained illuminated on the instrument panel. The diagnostic tool retrieved DTC B1650. Removed the passenger seat and lower B-pillar trim panel. Found water inside the pretensioner connector (yellow plug) beneath the seat. The pins had short-circuited due to electrolyte formation between them; resistance measured only 0.4 Ω. Cleaned the plug contacts with anhydrous ethanol, thoroughly dried with compressed air, applied special conductive grease, and reassembled. The resistance reading returned to 2.1 Ω. Cleared the DTC, resolving the fault. Recommend checking the vehicle floor sealing.
Original source ↗
BYD DTC AI AnalysisFrom Chinese market (translated)

BYD Qin Pro EV: Abnormal seatbelt pretensioner resistance after accident repair

✓
After replacing the front passenger seatbelt assembly on the collision-damaged vehicle, DTC B1650 set. Measured the old pretensioner resistance with a dedicated airbag tester: 0.6Ω (internal short); the new component measured 2.3Ω (normal). Further inspection found the impact had deformed the internal pins of the wiring harness connector, causing a short between the signal wire and earth. Replaced the wiring harness connector terminals and repaired the pretensioner to resolve the fault. Tip: On collision-damaged vehicles, pretensioners may have internal bridge wire fractures from impact, causing short circuits even when externally intact. Always verify by measuring resistance.
BYD DTC AI AnalysisFrom Chinese market (translated)

BYD Yuan EV: Seat modification caused wiring harness damage and short circuit

✓
After the owner self-installed full-coverage seat covers and seat heating pads, the SRS light came on. Inspection found that the fixing clips had pierced the pre-tensioner wiring harness beneath the passenger seat during installation, shorting the live wire to chassis ground. Measured resistance dropped to 0.3Ω. Removed the aftermarket accessories and stripped back the harness, revealing exposed copper conductors. Repair: cut out the damaged section, re-soldered the harness, insulated with double-layer heat-shrink tubing, rerouted the harness, and added corrugated tubing for protection, ensuring no interference with seat moving parts.
BYD DTC AI AnalysisFrom Chinese market (translated)

BYD Tang DM Intermittent B1650 Fault (Wiring Harness Wear)

✓
The DTC appeared intermittently. The SRS warning light came on after driving over rough roads. Diagnosis found the wiring harness retaining clip below the B-pillar had detached. As the seat moved back and forth, the metal bracket edge repeatedly pinched and chafed the harness, wearing through the insulation and causing the internal copper wires to short intermittently to ground. Re-secured the harness, wrapped it with fleece tape and corrugated tubing, and adjusted the slack to prevent contact with sharp edges. This completely resolved the fault. For intermittent faults like this, check for dynamic harness chafing.
Original source ↗
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]