AU
B16501A

DTC B16501A indicates the airbag system (SRS) detects the front passenger seat belt pretensioner resistance is below the calibrated threshold (typically below 1 — Qin Plus

Safety System

DTC B16501A indicates the airbag system (SRS) detects the front passenger seat belt pretensioner resistance is below the calibrated threshold (typically below 1.0Ω-1.5Ω; normal range is approximately 2.0Ω-3.5Ω; refer to the repair manual for exact specifications).

The seat belt pretensioner is a pyrotechnic actuator containing a resistance wire (squib) and an ignition charge.

Low resistance typically indicates an internal short circuit in the pretensioner, a wiring harness short to ground, a short between connector terminals, or a sampling circuit fault in the SRS control module (ACU).

This fault causes the SRS to register a pretensioner circuit fault, illuminate the airbag warning lamp, and potentially fail to deploy the front passenger seat belt pretensioner during a collision, severely compromising occupant protection.

3
Cases Logged
5
Causes
Likely Causes — Qin Plus
  • 1Front passenger seat belt pretensioner internal short circuit: Moisture, aging, or manufacturing defects short-circuit the squib's internal resistance wire, dropping resistance to nearly 0 Ω.
  • 2Harness short to ground: Wear, crushing, or rodent bites damage the wire insulation of the pretensioner harness under the seat or near the B-pillar, grounding the wire to the vehicle body.
  • 3Connector fault: Water ingress, oxidation, backed-out terminals, or a short circuit between terminals in the yellow pretensioner connector (usually located under the seat or inside the B-pillar trim), causing abnormal resistance.
  • 4SRS control module (ACU) internal fault: Damaged internal sampling circuit causes a false low resistance report (confirm after ruling out wiring faults).
  • 5Improper modification or repair: Fixing screws pierced the wiring harness during installation of seat heating pads or full-coverage seat covers, or incorrectly seated connectors during previous repairs caused bent pins and 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 system capacitors and prevent accidental airbag deployment.
  • 2
    Visual inspection: Remove the front passenger seat (or move it fully forward or backward). Inspect the seat belt pretensioner connector (usually a yellow plug) for looseness, water ingress, or oxidation. Inspect the wiring harness under the seat and at the B-pillar for signs of abrasion, crushing, or damage.
  • 3
    Resistance measurement: Use a multimeter to measure the resistance between the pretensioner connector terminals. Standard resistance is 2.0-3.5Ω (refer to the specific vehicle workshop manual). If the resistance is <1.0Ω, disconnect the pretensioner plug and measure the component directly. If the resistance remains low, replace the pretensioner assembly.
  • 4
    Harness continuity check: Measure the resistance between the pretensioner connector terminal and body ground. The resistance should be infinite (>1MΩ). If continuity exists, this indicates a harness short to ground. Repair or replace the harness.
  • 5
    Cross-check: If the wiring harness and pretensioner measure normal, check the SRS ECU connector for oxidation. If necessary, test with a known-good pretensioner to confirm an internal ACU fault.
  • 6
    Component replacement and reset: After confirming the fault source, replace the faulty component (the pretensioner is usually integrated with the seat belt retractor; replace the entire assembly). Reconnect all connectors, install the seat, and connect the battery. Use VDS2000/VDS1000 to clear the fault codes and perform an SRS system self-check. Confirm no fault codes remain and the airbag warning light is off.
Real-World Cases
BYD DTC AI AnalysisFrom Chinese market (translated)

Qin Pro DM front passenger pretensioner wiring harness worn and shorted

✓
The airbag warning light illuminated intermittently. Read DTC B16501A. Inspected beneath the front passenger seat and found the pretensioner harness chafed at the seat rail mounting bracket. The damaged insulation caused the copper wire to short directly to earth; measured resistance 0.3Ω. Repaired the damaged harness section, wrapped it with abrasion-resistant corrugated tubing, and rerouted the harness. Added retaining clips to prevent interference with the seat frame. Fault resolved.
Original source ↗
BYD DTC AI AnalysisFrom Chinese market (translated)

Qin Plus DM-i front passenger seat belt pretensioner connector water ingress and oxidation

✓
After the vehicle sat through heavy rain, the airbag warning light stayed on. Scan tool showed DTC B16501A. Inspected the pretensioner connector (yellow plug) under the front passenger seat and found water stains and copper oxide inside, shorting the terminals. Pretensioner circuit resistance measured only 0.8 Ω. Cleaned the terminals with WD-40 precision electrical contact cleaner, dried them with compressed air, and applied dielectric silicone grease. Cleared the fault code and it has not returned.
Original source ↗
BYD DTC AI AnalysisFrom Chinese market (translated)

Seat cover installation caused pretensioner wiring short circuit on Han EV

✓
Owner reported dashboard displayed 'Check Airbag System' after starting the vehicle, DTC B16501A. Inspection found recently fitted full-surround seat covers; the mounting clip screws had pierced the pretensioner wiring harness, creating an internal short between positive and negative wires. Resistance measured 0.5Ω. Removed the damaged clips and repaired the harness—cut out the damaged section, reconnected and soldered the wires. Restored harness to original routing. Fault resolved. Advised owner to avoid seat covers with invasive fixing methods.
Original source ↗
Other Qin Plus 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]