AU
B1650-00

DTC B1650-00 indicates the passenger seat belt pretensioner circuit resistance falls below the normal threshold set by the SRS control module (typically <2 — Seal U

Safety System

DTC B1650-00 indicates the passenger seat belt pretensioner circuit resistance falls below the normal threshold set by the SRS control module (typically <2.0Ω; normal range is 2.0-3.0Ω).

The pretensioner contains a pyrotechnic squib.

The ECU continuously monitors the squib resistance using a low-current signal.

Low resistance typically indicates a short to ground in the squib circuit, a ground fault from damaged wiring insulation, an internal connector short, or an internal short within the pretensioner component.

This fault forces the SRS system into a degraded mode, meaning the pretensioner may fail to deploy during a collision (seat belt fails to tighten) or may deploy inadvertently (unexpected firing).

ISO 15031 and BYD safety system design classify this as a Level 2 safety fault requiring immediate repair.

5
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Wiring harness wear under the seat or inside the B-pillar causing a short to ground: Frequent fore-and-aft adjustment of the front passenger seat or passenger foot movement wears through the harness insulation, grounding the copper core to the vehicle body.
  • 2Pretensioner internal component short circuit: Moisture ingress, aging, or manufacturing defects in the squib cause a short circuit in the internal resistance wire, dropping resistance to <1.0Ω.
  • 3Connector short circuit: Bent pins, backed-out pins, or corrosion from water ingress in the yellow SRS connector (usually located under the seat or inside the B-pillar trim) causing a short circuit between pins or to ground.
  • 4SRS ECU detection circuit fault: An abnormal ECU internal A/D conversion circuit or sampling resistor causes the ECU to incorrectly read the pretensioner resistance as too low.
  • 5Improper modification: Splicing into the SRS wiring harness when adding seat heating, ventilation, or massage functions, causing abnormal parallel resistance or a short circuit.
What To Do
  • 1
    Safe power-down: Turn off the ignition, disconnect the negative battery terminal, and wait at least 90 seconds to fully discharge the SRS capacitor and prevent accidental airbag deployment.
  • 2
    Fault Confirmation and Freeze Frame Recording: Use the VDS2000/VDS1000 diagnostic tool to read the fault code, confirm B1650-00 is a current fault (Active), and record freeze frame data (mileage, temperature, voltage, etc.).
  • 3
    Visual inspection: Remove the front passenger seat (if necessary) and the lower B-pillar trim. Inspect the yellow SRS connector (usually marked P Pretensioner) for looseness, water ingress, corrosion, or physical damage. Inspect the wiring harness for signs of crushing or abrasion.
  • 4
    Resistance measurement (ECU side disconnected): Disconnect the SRS ECU connector. Use a multimeter to measure the pretensioner circuit resistance on the wiring harness side. If the resistance is <2.0 Ω, the fault is in the wiring harness or pretensioner. If normal (2.0-3.0 Ω), the fault may be in the ECU.
  • 5
    Insulation resistance test: Measure the insulation resistance between the pretensioner wiring harness and body ground. The resistance must be >1 MΩ. If the resistance is low (<10 kΩ), this confirms a short to ground. Inspect the harness section by section to locate the point of damage.
  • 6
    Pretensioner unit test (caution): Disconnect the pretensioner connector and measure the resistance directly across the pretensioner plug terminals. Normal resistance is 2.0±0.3Ω. If <1.5Ω, replace the seat belt assembly (do not replace the pretensioner separately).
  • 7
    Connector pin inspection: Disassemble the SRS connector. Check the shorting bar for sticking causing a short circuit. Inspect the pins for bending, oxidation, or foreign matter.
  • 8
    Fault repair and replacement: Repair the damaged wiring harness (use solder and heat-shrink tubing; do not wrap with electrical tape), replace the short-circuited seat belt assembly, or replace the faulty ECU.
  • 9
    System verification: Restore all connections, connect the battery, and switch the ignition to ON for electrical self-check. Confirm the airbag fault warning lamp turns off. Use the diagnostic tool to clear the fault code and perform the SRS system function test (simulated crash signal test without triggering actual ignition).
Real-World Cases
BYD DTC AI AnalysisFrom Chinese market (translated)

Qin Pro front passenger seat wiring harness chafed, short to ground

✓
Symptom: Airbag warning light on instrument cluster stays on. Read DTC B1650-00 (passenger pretensioner resistance too low). Diagnosis: Checked wiring harness under passenger seat. Found that the seat rail fixing clip had chafed through the insulation of the yellow SRS harness over time, causing the copper conductor to short to the seat frame. Measured resistance: 0.8Ω. Repair: Cut out the damaged section and repaired it by soldering in high-temperature wire. Insulated the repair with double-layer heat shrink tubing. Rerouted the harness and added a protective sleeve. Cleared fault codes. Fault resolved.
Original source ↗
BYD DTC AI AnalysisFrom Chinese market (translated)

Song MAX front passenger pretensioner internal short circuit

✓
Symptoms: After sitting overnight, the airbag warning light stayed on at startup. No collision history. DTC B1650-00. Diagnosis: Disconnected the passenger side seatbelt pretensioner connector. Measured pretensioner internal resistance: 1.2 Ω (low). Measured harness ground resistance: >1 MΩ (normal). Determined the internal igniter had shorted from moisture ingress. Repair: Replaced the passenger side seatbelt assembly (includes pretensioner). Torqued the pretensioner mounting bolts to 9–11 N·m. Cleared fault codes. System returned to normal.
Original source ↗
BYD DTC AI AnalysisFrom Chinese market (translated)

Yuan EV passenger-side B-pillar connector water ingress short circuit

✓
Symptoms: After rainfall, started the vehicle and the airbag warning light illuminated. The scan tool displayed B1650-00. Diagnosis: Checked the SRS connector located beneath the B-pillar and found the connector seal had deteriorated. Rainwater ingress caused a short circuit between the pins, measuring 1.5Ω. After cleaning the water stains, the resistance returned to normal, but the connector had oxidised. Repair: Replaced the SRS connector (yellow waterproof plug), crimped the terminals using a special crimping tool, rewrapped the joint with waterproof tape, and cleared the fault.
Original source ↗
BYD DTC AI AnalysisFrom Chinese market (translated)

Tang DM: Pretensioner resistance abnormal after collision

✓
Symptoms: After a low-speed impact (front bumper damaged), the airbags did not deploy but the warning light came on. DTCs B1650-00 and B1651-00 stored. Diagnosis: The impact sensor triggered but didn’t reach the airbag deployment threshold. The impact caused the passenger-side pretensioner’s internal resistance wire to shift and short-circuit. Resistance measured 1.8 Ω. Repair: Replaced the passenger seatbelt assembly (the pretensioner is single-use; replace if triggered or damaged). Used a scan tool to perform SRS system configuration and calibration, then cleared the fault codes.
Original source ↗
BYD DTC AI AnalysisFrom Chinese market (translated)

BYD Qin EV450 ECU falsely reporting low resistance

✓
Symptoms: Intermittent B1650-00, occurring when cold and disappearing when warm. Wiring harness and pretensioner measurements were normal. Diagnosis: Used an oscilloscope to check the SRS ECU sampling signal. Found internal reference voltage drift in the ECU, causing it to misjudge the pretensioner resistance as too low under cold conditions. Solution: Replaced the airbag control module (SRS ECU) and performed online matching programming (writing the vehicle VIN and configuration codes). This completely resolved the fault.
Other Seal U 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]