AU
B16C6

DTC B16C6 (Left Front Seat Belt Pretensioner Deployment Control Circuit Low) indicates a low voltage or open circuit in the left front (driver side) seat belt pretensioner deployment control circuit — Seal U

Safety System

DTC B16C6 (Left Front Seat Belt Pretensioner Deployment Control Circuit Low) indicates a low voltage or open circuit in the left front (driver side) seat belt pretensioner deployment control circuit.

This SRS (Supplemental Restraint System) subsystem fault involves the pyrotechnic pretensioner inside the seat belt retractor and its control circuit.

The airbag control unit (ACU) sets this DTC when it detects pretensioner circuit resistance outside the standard range (normally 2.0±0.1Ω), an open circuit, a short to ground, or abnormal voltage.

This fault forces the airbag system into a degraded mode.

During a collision, the left front seat belt pretensioner may fail to deploy and retract, severely compromising driver protection.

The instrument panel SRS warning lamp remains illuminated to indicate system failure.

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Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Seat belt pretensioner internal open circuit or abnormal resistance: Aging, moisture ingress, or manufacturing defects in the internal igniter or resistance wire cause the resistance value to deviate from the standard range.
  • 2Poor connector contact: The dedicated yellow connector between the pretensioner and wiring harness has backed-out terminals, bent pins, oxidation, corrosion, or an incompletely engaged locking tab, causing intermittent or permanent poor contact.
  • 3Wiring harness mechanical damage: Frequent fore-and-aft seat adjustment, modification work, or assembly process issues cause internal copper wire breakage or insulation damage in the wiring harness under the seat, A-pillar, or door sill area.
  • 4Ground circuit fault: Loose bolts, corrosion, or uncleaned paint at SRS system grounding points (usually near the left front door sill, dashboard crossmember, or seat rail) causing excessive ground resistance.
  • 5ACU internal fault: Damaged internal drive circuit or sampling circuit in the airbag control unit, or abnormal software calibration, triggering a false pretensioner circuit fault.
What To Do
  • 1
    Safety Preparation and Diagnostic Confirmation: Use VDS or a dedicated diagnostic tool to read the fault code. Confirm B16C6 is a Current fault, not a History fault. Record the freeze frame data. Turn off the ignition, disconnect the negative battery terminal, and wait at least 3 minutes to fully discharge the SRS capacitor.
  • 2
    Visually inspect the connector: Remove the left front B-pillar lower trim panel and check the connection of the yellow dedicated seat belt pretensioner connector. Confirm the locking tab is fully engaged, with no looseness, water ingress, or foreign matter. Inspect the pins for bending, oxidation, burning, or push-out. Use the dedicated tool to repair if necessary.
  • 3
    Pretensioner resistance measurement: Disconnect the pretensioner connector and use a digital multimeter to measure the pretensioner body resistance. The standard value is 2.0 ± 0.1 Ω. If the resistance is infinite (open circuit) or close to 0 Ω (short circuit), replace the left front seat belt assembly (the pretensioner is not serviceable separately).
  • 4
    Harness continuity and insulation test: Inspect the wiring harness under the seat, inside the A-pillar trim panel, and at the door sill. Focus on the areas near the seat slide rails and harness pass-through holes. Measure wiring harness continuity between the pretensioner connector and the ACU. Check for open circuits, shorts to ground, or shorts to power. Repair or replace damaged wiring harness sections.
  • 5
    Ground point inspection: Check the ground points at the left front door sill, the left side of the instrument panel, and near the seat rail. Verify the ground bolt tightening torque meets the standard (usually 8-10 N·m) and the grounding surfaces are clean and free of paint and corrosion. Sand the surfaces and apply conductive grease if necessary.
  • 6
    ACU and system reset: If the pretensioner and wiring harness are normal, check the ACU output terminal signal. Perform coding configuration before replacing the ACU. After completing all repairs, reconnect the battery, clear the fault codes, and perform an SRS system self-check cycle (turn the ignition switch to the ON position and wait at least 6 seconds). Confirm the warning light turns off and does not reappear.
Real-World Cases
BYD DTC AI Analysis

BYD Tang DM left front seat belt pretensioner wiring broken

✓
Symptom: SRS warning light came on suddenly while driving. No collision history. Diagnosis: VDS scan retrieved active fault code B16C6 (Left Front Seat Belt Pretensioner Circuit Low). Removed the left front seat and found the internal copper wire of the under-seat harness had broken from fatigue due to frequent forward/backward seat adjustment. Also noted slight oxidation on the pretensioner connector. Measured normal pretensioner resistance, but harness continuity test showed an open circuit. Repair: Replaced the left front seat belt assembly (including pretensioner) as a preventive measure. Repaired the broken harness wire under the seat and added protective sleeving. Rerouted and secured the harness routing to avoid interference with the seat rails. Cleared the fault code and the system returned to normal.
Original source ↗
BYD DTC AI Analysis

BYD Song Pro: Seat modification caused poor pretensioner connector contact.

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Symptoms: After starting the vehicle, the dashboard showed 'Check Airbag System' and the warning light stayed on. The owner reported having the seats reupholstered in leather a week before. Diagnosis: Retrieved DTC B16C6 (Driver Side Seatbelt Pretensioner Circuit Fault). Removed the driver's seat and found the yellow pretensioner connector had been disconnected during the modification and not fully reseated, preventing the locking tab from engaging. The pins were slightly bent. Resistance across the pretensioner measured open circuit. Repair: Straightened the bent pins using specialized tools, cleaned the connector contacts, and firmly reconnected the plug to ensure the locking tab engaged properly. Cleared the fault codes with a diagnostic tool and ran an airbag system self-test. Fault resolved.
Original source ↗
BYD DTC AI Analysis

BYD Qin Plus: Poor ground connection causing intermittent fault

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Symptoms: After about 20,000 km, the airbag warning light illuminated intermittently, sometimes going out on its own after driving for a while, with no regular pattern. Diagnosis: With the warning light on, retrieved current fault code B16C6 (Left Front Seatbelt Pretensioner Circuit Voltage Low). Inspection found the pretensioner connector locking tab not fully seated; wiggling the wire harness reproduced the fault. Further inspection revealed a loose ground bolt at the left front sill, causing unstable resistance in the SRS circuit. Resolution: Tightened the ground bolt to the specified torque, sanded the mating surface to remove oxidation, and applied conductive paste to prevent further oxidation. Replaced the pretensioner connector lock (the retaining clip had fatigued). Re-routed and secured the wiring harness properly. Cleared the fault code and monitored the vehicle for one week; the fault did not recur.
Original source ↗
BYD DTC AI Analysis

BYD Han EV: New vehicle assembly defect caused pinched wiring harness

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Symptoms: One week after taking delivery, the SRS warning light stayed on. No accident history; the vehicle drove normally. Diagnosis: The dealership scanned the vehicle and retrieved DTC B16C6 (Driver seatbelt pretensioner deployment control circuit low). They checked the pretensioner connector and found a normal connection. They measured the pretensioner resistance at 2.0Ω, within specification. They inspected the wiring harness between the SRS control unit (ACU) and the pretensioner and found an assembly fixture inside the A-pillar trim had crushed it. Stripping back the harness insulation revealed internal copper wires partially fractured but not completely severed, causing intermittent poor contact. Repair: They replaced the damaged harness section between the A-pillar and the pretensioner, rerouted the wiring to avoid the crush point, and fitted protective corrugated tubing. This completely resolved the fault. Root cause: Factory assembly quality control issue.
Original source ↗
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.