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B17801B

DTC B17801B indicates the SRS (Supplemental Restraint System) control unit detects an open circuit in the right middle-row seat belt pretensioner circuit (resistance exceeds the normal range, typically >10Ω or infinite) — Atto 3

Safety System

DTC B17801B indicates the SRS (Supplemental Restraint System) control unit detects an open circuit in the right middle-row seat belt pretensioner circuit (resistance exceeds the normal range, typically >10Ω or infinite).

This fault essentially constitutes a 'passenger restraint system communication loss'.

During a collision, the pretensioner for this seat cannot receive the ignition signal and fails to retract the seat belt at the moment of impact to eliminate slack between the occupant and the belt.

This fault triggers the SRS downgrade protection strategy, potentially altering the airbag deployment logic for this seat and surrounding areas (such as delayed deployment or non-deployment), severely compromising passive safety performance.

For BYD E2/E3/Qin EV models, the right middle row typically refers to the second-row right seat.

The pretensioner integrates into the seat belt retractor and communicates with the SRS ECU via a dedicated yellow connector under the seat.

5
Cases Logged
Real-World Cases
BYD DTC AI Analysis

Wear on the right second-row seat rail severed the pretensioner wiring harness on the E3 ride-hailing vehicle.

✓
A BYD E3 rideshare vehicle with 120,000 km came in with the SRS warning light constantly illuminated. Scanned and retrieved DTC B17801B. Inspection revealed frequent seat sliding adjustments during commercial operation had chafed the wiring harness sheath at the right middle seat runner. Two internal conductors had completely fractured, though externally only minor scratches were visible. Repair: Cut out the damaged section, resoldered using 0.5 mm² high-temperature-resistant wire, insulated with double-layer heat-shrink tubing, and adjusted the harness routing to increase slack and prevent future chafing. Fault resolved.
BYD DTC AI Analysis

Qin EV pretensioner connector not plugged in after accident repair

✓
2019 BYD Qin EV. After a right rear collision, a non-authorised garage replaced the right rear door and seat. The owner noticed the SRS warning light on. Diagnosis revealed the right rear seat pre-tensioner connector was completely unplugged (technician likely forgot to reconnect it). Reconnected the yellow connector, confirmed the locking tab engaged, cleared the fault codes, and the system returned to normal. After accident repairs, check all SRS component connections.
BYD DTC AI Analysis

E2: Aftermarket seat replacement resulted in missing pretensioners

✓
The BYD E2 owner replaced the right-hand second-row seat assembly with an aftermarket unit after the original seat was damaged. After the replacement, the instrument cluster displayed an SRS warning. Inspection revealed the aftermarket seat lacked a seatbelt pretensioner and the connector hung loose. Solution: Installed an OEM seat assembly with the pretensioner, reconnected the wiring and configured the seat presence sensor parameters. DTC B17801B cleared.
BYD DTC AI Analysis

Pretensioner internal igniter open circuit due to aging

✓
An E3 parked for several days threw a B17801B immediately after startup. Connectors checked good and harness continuity was normal, but the pretensioner body measured infinite resistance. Disassembly found oxidized, fractured igniter terminals inside (likely from long-term humidity). Replaced the seatbelt pretensioner assembly (requires replacing the retractor as well). Fault cleared.
BYD DTC AI Analysis

SRS control unit software false positive (intermittent fault)

✓
Qin EV owner reported the SRS warning light comes on intermittently. Historical DTC B17801B present; current status shows historical fault. Checked wiring and resistance—normal. Suspected outdated SRS ECU software causing overly sensitive resistance threshold detection. Solution: Upgraded SRS control unit software to V2.1 or higher and cleared adaptive learning values. No recurrence after one month of monitoring.
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: Community This information is for reference only. Always consult a qualified technician for diagnosis and repair. Do not attempt high-voltage system repairs yourself.