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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 — Seal U

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 — Seal U
  • 1Pretensioner squib internal short circuit: Damaged heating wire insulation inside the pretensioner body shorts the positive and negative terminals, usually resulting from manufacturing defects or hidden damage in an unreplaced pretensioner after an accident.
  • 2Wiring harness damaged and shorted to ground: Frequent seat sliding, compression by foreign objects, or abrasion against metal edges damages the pretensioner wiring harness insulation under the front passenger seat or inside the B-pillar trim panel, causing a short to body ground.
  • 3Connector water ingress, corrosion, and short circuit: Vehicle wading, car washing, or a leaking sunroof allows water to enter the pretensioner connector (usually located below the B-pillar or under the seat), causing electrolytic conduction between the pins and resulting in a short circuit.
  • 4SRS control unit internal fault: A damaged ACU internal monitoring circuit causes a false short-circuit reading, while actual pretensioner and wiring harness resistance values are normal.
  • 5Improper collision repair: failing to fully disconnect the pretensioner connector when replacing the front passenger airbag or seat belt after a collision, causing a short circuit, or installing an aftermarket pretensioner with an incorrect resistance value.
What To Do
  • 1
    Safe power-down: Turn off the ignition, disconnect the 12V battery negative terminal, and wait at least 3 minutes to fully discharge the SRS system high-voltage capacitor 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 reoccurs 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 the seat side trim panel.
  • 4
    Connector check: Disconnect the pretensioner connector and visually inspect the inside of the connector for signs of water ingress, terminal corrosion, Green Crimp (verdigris), or bent terminals causing a short circuit. Clean with electrical contact cleaner if necessary.
  • 5
    Resistance measurement: Use a multimeter to measure the pretensioner body resistance (connector side). Normal value: 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 reading must be infinite. If continuity exists, inspect and repair the wiring harness.
  • 6
    Wiring harness inspection: Trace the pretensioner wiring harness routing (via the floor harness to the ACU) and check for pinched, damaged, or chafed points. Focus on the areas near the seat slide rail and B-pillar pass-through. Repair and re-wrap any damaged wiring harness.
  • 7
    Insulation test: Use a megohmmeter to measure the insulation resistance between the pretensioner circuit and the vehicle body. Resistance must be greater than 1MΩ to rule out intermittent short circuits.
  • 8
    Component replacement: If diagnostics confirm an internal short circuit in the pretensioner, replace the OEM front passenger seat belt assembly (the pretensioner is usually unavailable separately; replace the complete seat belt retractor assembly). Verify the part number matches the vehicle model.
  • 9
    System verification: Reconnect all connectors and the 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 perform the active test function; this only checks circuit continuity and does not trigger deployment) 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 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]