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 — Atto 3

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 — Atto 3
  • 1Front passenger seat belt pretensioner internal short circuit: Moisture, aging, or manufacturing defects short-circuit the squib's internal resistance wire, dropping the resistance to nearly 0 Ω.
  • 2Harness short to ground: Wear, crushing, or rodent chewing damages the wire insulation on the pretensioner harness under the seat or near the B-pillar, causing contact with the vehicle body ground.
  • 3Connector fault: Water ingress, oxidation, backed-out terminals, or short circuit between terminals at 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 reading (confirm after ruling out wiring faults).
  • 5Improper modification or repair: Retaining screws piercing the wiring harness when installing seat heating pads or full-coverage seat covers, or failing to seat the connector correctly during previous repairs, causing bent pins and a short circuit.
What To Do
  • 1
    Safe power-down: Turn off the ignition switch, disconnect the battery negative terminal, and wait at least 90 seconds to fully discharge the SRS system capacitor and prevent accidental airbag deployment.
  • 2
    Visual inspection: Remove the front passenger seat (or move it to the fully forward/rearmost position). 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. Normal resistance is 2.0-3.5Ω (refer to the specific vehicle repair manual). If 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. Resistance must be infinite (>1 MΩ). If continuity exists, the harness is shorted to ground. Repair or replace the harness.
  • 5
    Cross-check: If wiring harness and pretensioner measurements are normal, inspect 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 usually integrates with the seat belt retractor; replace the entire assembly). Reconnect all connectors, install the seat, and connect the battery. Use the VDS2000/VDS1000 to clear the fault codes and perform an SRS system self-check. Confirm no fault codes remain and the airbag warning light turns 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 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: 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]