B164A – Front passenger seatbelt pretensioner not connected (BYD)

B164A means the front passenger seatbelt pretensioner circuit is being seen as “not connected,” and that usually turns the SRS/airbag warning on and may reduce occupant protection in a crash. In plain terms, the car thinks the passenger-side belt pretensioner isn’t electrically present, so the system can’t rely on it. According to BYD factory diagnostic data, this is a BYD-defined body/SRS-related code for “Front passenger seatbelt pretensioner not connected,” and manufacturer-specific codes like this can vary by BYD platform and model year. Treat it as a safety-critical fault: follow BYD SRS depowering procedures before touching any related connectors.

B164A Quick Answer

This code points to an open or disconnected front passenger seatbelt pretensioner circuit on a BYD, most often caused by a loose/contaminated connector or wiring issue at the seat/buckle/pretensioner assembly—not a confirmed bad part until the circuit is verified with OEM-approved methods.

What Does B164A Mean?

Official definition (BYD): “Front passenger seatbelt pretensioner not connected.” What the module detected: the SRS/occupant restraint control logic is not seeing the expected electrical presence of the front passenger pretensioner. What that means in practice: the airbag/SRS system will typically illuminate a warning and may disable or limit deployment strategy for the passenger belt pretensioner because it cannot confirm the device is connected and ready.

What it is actually checking (technical): the SRS controller monitors the pretensioner firing loop and connector integrity using internal diagnostics (continuity/plausibility checks and circuit supervision). B164A sets when the measured condition looks like an open circuit/disconnect at the pretensioner, connector, harness, or intermediate coupler. Why that matters for diagnosis: the message points to a suspected trouble area (loop integrity), not a guaranteed failed pretensioner; the correct next step is safe depowering and circuit/connector verification using BYD-approved test procedures—never back-probe or ohm-check the igniter with standard leads.

Theory of Operation

Under normal conditions, the BYD Dolphin’s SRS system continuously supervises each restraint “firing loop,” including the front passenger seatbelt pretensioner. The pretensioner is a pyrotechnic device integrated into the belt system, and the SRS controller expects to see a stable, in-range loop signature through dedicated wiring and connectors. If the system detects a crash meeting deployment criteria, it commands current to the pretensioner to tighten the belt early in the event.

For B164A, that normal supervision fails because the controller sees the passenger pretensioner as electrically missing. The usual breakdown is not “it didn’t deploy,” but “it can’t be confirmed connected”: an unplugged connector under the seat, a partially latched connector, terminal push-out, harness damage from seat movement, corrosion/contamination, or an incorrect component/connector mating after interior work. Because this is a safety-critical circuit, BYD procedures require the SRS to be depowered before any connector handling, and only OEM-approved test methods should be used to avoid accidental deployment or module damage.

Symptoms

Typical symptoms you’ll notice with B164A on a BYD include:

• SRS warning illuminated on the instrument cluster (often airbag/seatbelt symbol or “SRS” message)
• Passenger restraint status messages indicating a restraint/airbag system fault, depending on cluster software
• Stored SRS DTC B164A present in SRS/Body-related diagnostics (may be current or history)
• Inspection failure because the SRS light is on (where safety inspections apply)
• Intermittent fault that appears after moving the passenger seat fore/aft or changing seat height (harness strain symptom)
• Post-repair onset immediately after seat removal, upholstery work, console work, or wiring accessory installation near the seat
• Reduced protection potential for the front passenger belt pretensioner function due to a supervised circuit fault

Common Causes

• Front passenger pretensioner connector not fully seated: A partially latched connector at the seatbelt buckle/pretensioner or seat-base junction creates an intermittent open that the SRS module interprets as “not connected.”
• High resistance from corrosion or terminal fretting: Light oxidation or micro-movement at terminals increases resistance enough that the SRS module sees an out-of-range circuit condition even though the connector appears plugged in.
• Harness damage under the front passenger seat: Seat track movement, pinching, or abrasion can break conductors internally, producing an open circuit that flags a “not connected” DTC.
• Poor terminal tension or backed-out pin: A spread terminal or a pin that has pushed back in the connector housing prevents reliable contact and mimics an unplugged pretensioner.
• Previous seat removal/repair with improper reconnection: After interior work, the pretensioner circuit may be routed incorrectly, left disconnected, or latched to the wrong mate, triggering B164A immediately at key-on.
• Incorrect or non-approved seat/seatbelt component installed: A mismatched BYD Dolphin seatbelt/pretensioner assembly or sub-harness can present an unexpected electrical signature that the SRS module treats as “not connected.”
• Wiring splice/repair not SRS-compliant: Non-OEM splices, crimp connectors, or repairs near the SRS harness can introduce resistance/opens and are commonly responsible for repeat faults.
• Fault in the SRS wiring between seat connector and SRS control module: An open or high resistance in the body-side harness (not the pretensioner itself) can cause the same “not connected” detection.

Diagnosis Steps

Tools: a scan tool with full BYD SRS access (DTCs, freeze frame/event data, and live data), OEM wiring diagrams and connector views, a quality DMM, and approved SRS test equipment/procedures. Do not back-probe SRS connectors with standard leads or use a test light. Depower/disable the SRS system using OEM procedures before touching any pretensioner-related connector.

1. Confirm the DTC and capture event data: Using an SRS-capable scan tool, read all SRS/Body DTCs and record B164A status (stored/confirmed vs history). Save freeze frame/event parameters relevant to a circuit DTC: battery voltage, ignition state, and any companion SRS codes. Freeze frame shows the conditions when B164A set; a scan tool snapshot is different and can be triggered later to catch an intermittent dropout while you wiggle-test.
2. Perform a quick visual check of the circuit path before meter work: With ignition OFF and following BYD SRS depowering procedure, inspect the front passenger seat area for signs of recent seat removal, interior work, water intrusion, crushed loom, or harness tension. Confirm the under-seat harness is properly routed and not trapped in the seat track. Do not unplug SRS connectors until the system is depowered per OEM steps.
3. Check fuses and power distribution first (do not start at the module): Identify the SRS/Body power feeds in BYD service information and verify related fuses are correct rating and seated. Confirm the fuse box and power distribution connections are tight and clean. A low-voltage event can create false SRS circuit faults; compare freeze frame battery voltage to current system voltage and charging condition.
4. Verify SRS module power and ground with voltage-drop testing under load: With the vehicle in the correct state per service info (typically ignition ON for module operation) and using OEM-approved test points/methods, perform voltage-drop tests on SRS ECU grounds while the circuit is operating. Ground drop must be less than 0.1 V under load. Do not rely on continuity checks alone—high resistance can pass continuity but fail under load.
5. Inspect and secure the front passenger pretensioner circuit connectors: Depower SRS again before disconnecting anything. Locate the front passenger seatbelt pretensioner/buckle connector(s) and any intermediate under-seat connector. Check for incomplete latching, CPA/secondary locks not engaged (if used), damaged housings, moisture, debris, or pulled wires. Look closely for backed-out terminals and poor terminal tension signs.
6. Check harness integrity along the seat movement zone: With SRS depowered, inspect the harness where it flexes with seat travel. Look for flat spots, cuts, or pinch points at seat rails and brackets. Perform a gentle tug test at each wire near the connector to find broken conductors inside insulation. If you find damaged loom, open it and inspect each conductor; do not “twist and tape” any SRS wiring.
7. Use scan tool live data to validate the fault is circuit-related and repeatable: After re-securing connectors and restoring the system per OEM procedure, view SRS live data/PIDs that reflect passenger pretensioner status (naming varies by BYD platform). Key ON and observe whether the status toggles while lightly manipulating the harness (wiggle test). If the fault is hard, it will typically return quickly at key-on on a continuously monitored circuit.
8. Perform OEM-approved circuit tests (no improvised probing): Follow BYD service information for pretensioner circuit checking. Use only approved breakout leads/adapters or test harnesses designed for SRS connectors. Verify the circuit for opens/high resistance between the pretensioner connector and the body-side harness path. If service info calls for a specified load tool or simulator, use it; do not substitute resistors or apply power to the pretensioner circuit.
9. Differentiate component vs wiring by isolation: If wiring checks good up to the under-seat/body harness connector, isolate the section that moves with the seat from the fixed body harness. A fault that changes with seat position strongly indicates a harness/connector issue in the seat-side section rather than the SRS ECU. If the fault persists regardless of seat movement, focus on connector pin fit, corrosion, or the body-side harness path.
10. Confirm the repair without “clear-and-hope”: After correcting the verified issue, reassemble and secure the harness routing so it cannot be pinched through full seat travel. Use the scan tool to clear SRS DTCs only after the fault is corrected, then cycle ignition and recheck for immediate return. Perform a controlled functional verification (key cycles and seat movement) and confirm no current/pending SRS faults reappear.

Professional tip: On BYD vehicles, under-seat SRS connectors are frequently disturbed by seat movement or prior interior work. If B164A resets immediately after key-on, treat it as a hard “open/high resistance” condition and focus on connector latch/terminal fit and the flexing harness segment first. Always use OEM-approved SRS test adapters—standard meter probes can spread terminals and create the very “not connected” problem you’re chasing.

Possible Fixes

• Reseat and correctly lock the front passenger pretensioner connector(s): Restore proper engagement of primary latch and any secondary lock after verifying terminals are correctly positioned.
• Repair damaged wiring in the under-seat harness section: Replace or OEM-approved repair of the affected harness segment where pinching/abrasion/open circuit was confirmed.
• Correct terminal issues: Replace/repair backed-out, spread, or corroded terminals using proper BYD terminal service procedures and parts.
• Restore correct harness routing and retention: Reclip/secure the loom so it cannot contact seat rails and has adequate slack through full seat travel.
• Replace the seatbelt pretensioner/buckle assembly only after circuit proof: If the wiring/connector path is verified good with approved methods and the fault isolates to the pretensioner side, replace the matched BYD part per OEM procedure.
• Address power/ground integrity issues affecting SRS monitoring: Clean/repair confirmed high-resistance grounds or power distribution faults found by voltage-drop testing under load.

Can I Still Drive With B164A?

You can usually drive a 2020 BYD Dolphin with DTC B164A present, but you should treat it as a safety-critical condition rather than “just a warning light.” This code indicates the front passenger seatbelt pretensioner circuit is seen by the SRS as not connected, which means the occupant protection strategy for the front passenger position may be compromised in a crash. Driving the vehicle does not typically create immediate drivability problems, but it does increase risk because the SRS may disable that pretensioner (and in some strategies, may alter related deployment decisions). Do not attempt DIY probing or connector work on SRS circuits; the system must be depowered using BYD procedures before any inspection.

How Serious Is This Code?

B164A is serious because it involves the SRS restraint system and specifically a component that tightens the passenger belt during a collision. In day-to-day driving it may be “inconvenient” in the sense that the vehicle still operates normally, but it is a safety issue because the front passenger protection may not perform as designed. Assume the SRS is potentially compromised until proven otherwise. Proper diagnosis requires a scan tool with full BYD SRS access and OEM-approved test methods; standard test leads and improvised resistance checks can deploy a pretensioner or damage the SRS ECU. If you are not trained and equipped for SRS work, this is not a DIY repair.

Common Misdiagnoses

The most common mistake is replacing the front passenger seatbelt buckle/pretensioner assembly immediately because the description says “not connected.” On BYD platforms this DTC often sets from connection integrity problems: a partially seated under-seat connector, harness strain from seat travel, terminal tension loss, corrosion, or improper connector handling during interior work. Another frequent error is using a multimeter or test light directly on pretensioner circuits; that can skew readings, set more SRS faults, or create a safety hazard. Technicians also waste time clearing codes repeatedly instead of checking SRS live data for the pretensioner circuit status, verifying connector locks, and confirming continuity with OEM-approved methods only after the SRS is correctly depowered.

Most Likely Fix

The most frequently confirmed repair direction for B164A on a BYD is restoring a reliable connection at the front passenger seatbelt pretensioner circuit: correctly depower the SRS, then inspect the passenger seat/pretensioner connector for full engagement, secondary lock position, pushed-out terminals, and harness damage from seat movement; repair wiring/terminals as needed and secure the harness to prevent repeat strain. If circuit integrity checks and connector repairs do not restore normal pretensioner “connected” status in SRS data, the next common direction is replacing the affected pretensioner/belt assembly only after verifying power/ground paths and circuit continuity per BYD procedures, then confirming the repair with a full SRS self-test and re-scan.

Repair Costs

SRS/airbag repair costs vary significantly by component. Diagnosis must be performed by a qualified technician with SRS-capable equipment. Do not attempt airbag system repairs without proper training and safety procedures.

Last updated: March 29, 2026