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B1704-00

DTC B1704-00 indicates the SRS (Supplemental Restraint System) ECU detects an open circuit fault in the left curtain shield airbag ignition circuit — Seal U

Safety System

DTC B1704-00 indicates the SRS (Supplemental Restraint System) ECU detects an open circuit fault in the left curtain shield airbag ignition circuit.

The SRS ECU continuously monitors the airbag inflator circuit resistance via an internal diagnostic circuit.

When the resistance value exceeds the normal threshold (typically >10Ω or approaching infinity), the ECU registers a 'disconnected' state.

This fault prevents the left curtain airbag from deploying during a side impact, depriving the occupant's head of lateral impact protection and posing a severe safety hazard.

Interrupted electrical connections, damaged wiring harnesses, or a failed inflator within the airbag module can cause this fault.

4
Cases Logged
Real-World Cases
BYD DTC AI Analysis

Left B-pillar connector not reconnected after accident repair, causing intermittent warnings

✓
A 2018 Qin EV450 developed an intermittent airbag warning light after left front door sheet metal repair. VDS scan showed DTC B1704-00 (current). Removed the left B-pillar trim and found the curtain airbag connector (yellow) only partially inserted—about halfway—with the locking tab not engaged. The technician had removed interior trim during the repair and did not properly reseat the connector; the connector requires two audible clicks to confirm full engagement. Re-seated the connector fully and wrapped it with electrical tape for added security. Cleared the DTC; no recurrence.
BYD DTC AI Analysis

Blocked sunroof drain tube caused wiring harness corrosion and open circuit

✓
A 2019 BYD E1 developed a constant airbag warning light after heavy rain, logging DTC B1704-00. Inspection found water staining below the left A-pillar. Removing the headliner revealed the left curtain airbag harness connector covered in green copper corrosion; the severely oxidised pins caused contact resistance >50 Ω. Further inspection showed the left rear sunroof drain hose had detached, allowing rainwater to track down the A-pillar. Replaced the left curtain airbag harness assembly (including connector), cleaned the SRS ECU terminals, re-secured the drain hose, and resolved the fault.
BYD DTC AI Analysis

Aftermarket roof lining modification accidentally severed airbag harness.

✓
A 2017 BYD Qin 80 came in with an illuminated airbag warning light after a starlight headliner retrofit. The scan tool displayed DTC B1704-00. Disassembly revealed that the retrofit technician had accidentally drilled through the protective corrugated tubing of the curtain airbag wiring harness while drilling into the left roof rail, severing two wires. The curtain airbag wiring harness is a non-serviceable part integrated into the roof harness and cannot be repaired separately. The shop replaced the entire left roof wiring harness (including the curtain airbag branch) and coded and matched the SRS ECU to resolve the fault.
BYD DTC AI Analysis

Curtain airbag module internal squib open circuit due to aging

✓
The airbag warning light suddenly illuminated on a 2017 Qin EV300 with 120,000 km, logging DTC B1704-00. Resistance at the harness end measured 2.3 Ω (normal), but a direct measurement at the airbag module terminals showed open circuit (OL). Removed the left curtain airbag (after removing the front and rear sections of the headliner) and found a cold solder joint on the igniter pin inside the gas generator, causing the open circuit. Replaced the left curtain airbag module with a genuine part, performed the 'Replace Airbag Module' configuration procedure using a diagnostic tool, and fixed the fault. This is a rare but possible hardware failure mode in high-mileage vehicles.
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: Community This information is for reference only. Always consult a qualified technician for diagnosis and repair. Do not attempt high-voltage system repairs yourself.