AU
B164F1A

DTC B164F1A indicates the Airbag Control Unit (ACU) detects a front passenger seat belt pretensioner circuit resistance of 0 ohms or close to 0 ohms, determining a short circuit fault — Atto 3

Safety System

DTC B164F1A indicates the Airbag Control Unit (ACU) detects a front passenger seat belt pretensioner circuit resistance of 0 ohms or close to 0 ohms, determining a short circuit fault.

The pretensioner contains a pyrotechnic squib with a normal resistance between 1.5 and 3.0 Ω.

A resistance of 0 indicates an internal short circuit in the pretensioner, a wiring harness short to ground, or a pin-to-pin short at the connector.

This fault prevents the SRS system from triggering the front passenger seat belt pretensioner during a collision (failing to tighten the seat belt).

In extreme cases, the short circuit illuminates the airbag warning light continuously and locks the entire airbag system, severely compromising passive safety performance.

5
Cases Logged
5
Causes
Likely Causes — Atto 3
  • 1Pretensioner squib internal short circuit: Damaged insulation on the internal heating wire of the pretensioner body shorts the positive and negative terminals. Manufacturing defects or hidden damage in an unreplaced unit following an accident usually cause this fault.
  • 2Harness damaged and shorted to ground: Frequent seat sliding, pinching by foreign objects, or abrasion against metal edges damages the pretensioner harness insulation under the front passenger seat or inside the B-pillar trim panel, shorting the harness to the vehicle body.
  • 3Connector water ingress, corrosion, and short circuit: Vehicle wading, car washing, or sunroof leaks allow water to enter the pretensioner connector (usually located below the B-pillar or under the seat), causing electrolyte conduction between the pins and creating a short circuit.
  • 4SRS control unit internal fault: Damaged ACU internal monitoring circuit triggers a false short circuit, while actual pretensioner and wiring harness resistance is normal.
  • 5Improper accident repair: Failing to fully seat the pretensioner connector when replacing the front passenger airbag or seat belt after an accident, causing a short circuit, or installing an aftermarket pretensioner with an incorrect resistance value.
What To Do
  • 1
    Safe power-down: Switch off the ignition, disconnect the 12V battery negative terminal, and wait at least 3 minutes to fully discharge the SRS system high-voltage capacitors and prevent accidental airbag deployment.
  • 2
    Fault confirmation: Connect the VDS2000 or Launch X-431 diagnostic tool, read the SRS system fault codes, and confirm B164F1A is a current fault that returns after clearing.
  • 3
    Locate the pretensioner: Determine the front passenger seat belt pretensioner location based on the vehicle model (E2/E3/Qin EV) (usually integrated into the seat belt retractor, located below the B-pillar or on the outer side of the seat). Remove the lower B-pillar trim panel or seat side trim panel.
  • 4
    Connector inspection: Disconnect the pretensioner connector. Visually inspect the connector interior for signs of water ingress, terminal corrosion, green crimp (verdigris), or bent terminals causing a short circuit. If necessary, clean with electrical contact cleaner.
  • 5
    Resistance measurement: Use a multimeter to measure the pretensioner body resistance (connector side). Normal resistance is 1.5-3.0 Ω. If the reading is 0-0.5 Ω, replace the pretensioner. Measure the resistance to ground on the wiring harness side. The resistance must be infinite. If continuity exists, repair the wiring harness.
  • 6
    Harness inspection: Trace the pretensioner harness routing (via the floor harness to the ACU) and check for pinched, damaged, or worn-through points. Focus on the areas near the seat slide rail and B-pillar pass-through. Repair and re-wrap any damaged harness sections.
  • 7
    Insulation test: Use a megohmmeter to measure the insulation resistance between the pretensioner circuit and the vehicle body. The resistance must be greater than 1MΩ to rule out the risk of an intermittent short circuit.
  • 8
    Component replacement: If confirming an internal short circuit in the pretensioner, install an OEM front passenger seat belt assembly (the pretensioner is typically unavailable separately; replace the entire seat belt retractor assembly). Verify the part number matches the vehicle model.
  • 9
    System verification: Reconnect all connectors and the 12V battery negative terminal. Use the diagnostic tool to clear the fault code and perform an SRS system self-check. Confirm B164F1A does not return and the airbag warning light turns off.
  • 10
    Function test: Perform a simulated crash test (use the diagnostic tool to execute the active test function; this checks circuit continuity only and does not actually deploy the system) or perform a road test to confirm normal system operation.
Real-World Cases
BYD DTC AI AnalysisFrom Chinese market (translated)

BYD E2 front passenger pretensioner connector oxidised and shorted

✓
Symptoms: 2019 E2 airbag warning light stays on. Diagnostic scan tool retrieved DTC B164F1A (passenger pretensioner resistance 0 ohms). Diagnosis: Disconnected the pretensioner connector under the passenger seat and found obvious green corrosion inside the connector from previous water ingress. Measured pretensioner body resistance at 2.1 ohms (normal), but resistance across the connector pins was 0.3 ohms (short circuit). Repair: Cleaned the connector pins, applied conductive grease, and replaced the connector housing (with waterproof seal). Fault resolved.
Original source ↗
BYD DTC AI AnalysisFrom Chinese market (translated)

Qin EV seat rail pinched the pretensioner wiring harness, causing a short circuit.

✓
Symptoms: While driving the 2020 Qin EV over rough roads, the airbag warning light illuminated intermittently. Scanning revealed DTC B164F1A appearing intermittently. Diagnosis: Inspected the front passenger seat base and found the pretensioner wiring harness pinched at the foremost position of the seat rail. The damaged insulation let copper conductors contact the seat frame (ground). Resistance between the harness and ground fluctuated when shaking the seat. Repair: Repaired the damaged harness by re-wrapping it with insulation tape, rerouted the wiring and added corrugated tube protection, ensuring a minimum 20mm clearance from the seat rail.
Original source ↗
BYD DTC AI AnalysisFrom Chinese market (translated)

Passenger pretensioner internally shorted after accident repair

✓
Symptoms: After front collision repairs on a 2019 Qin EV, the airbag warning light stays on and DTC B164F1A cannot be cleared. Diagnosis: The passenger airbag deployed previously, but the seatbelt pretensioner was only reset—not replaced. Measured passenger pretensioner resistance: 0.2 Ω. The pretensioner's internal heating wire had deformed and short-circuited due to the earlier collision impact. Repair: Replaced the passenger seatbelt assembly (includes pretensioner, part number: MEF-3657940). Coded and configured with VDS. Fault code cleared.
Original source ↗
BYD DTC AI AnalysisFrom Chinese market (translated)

Liquid corrosion shorted the pins of the front passenger pretensioner connector.

✓
Symptom: The E3 owner reported spilling a beverage on the passenger seat, after which the airbag warning light remained on, logging DTC B164F1A. Diagnosis: Removed the passenger side lower B-pillar trim panel and found liquid residue inside the pre-tensioner connector. The residue created a conductive path between the pins; resistance measured close to 0Ω. Repair: Thoroughly cleaned the connector with isopropyl alcohol, blow-dried it, and replaced the waterproof seal. Advised the owner to prevent liquid from getting into the seat and to install waterproof seat covers if necessary.
Original source ↗
BYD DTC AI AnalysisFrom Chinese market (translated)

Wiring harness near front passenger seat belt buckle chafed through and shorted

✓
Symptoms: The Yuan Plus airbag light illuminated intermittently while driving. Diagnosed as DTC B164F1A. Diagnosis: Inspection found the wiring harness near the front passenger seatbelt buckle had chafed against the seat frame over time, causing both the pretensioner power supply and earth wires to wear through and short together, creating a 0Ω path. Repair: Repaired the damaged harness (section replacement), rerouted using abrasion-resistant corrugated tubing, and adjusted the retaining clip positions to prevent interference with moving parts.
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]