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B1784-00

This fault code indicates a low resistance or short circuit in the driver-side front airbag Stage 2 inflator circuit — Seal U

Safety System

This fault code indicates a low resistance or short circuit in the driver-side front airbag Stage 2 inflator circuit.

The SRS control unit detects a circuit resistance of 0 ohms (normal range: 2.0-3.0 ohms).

Dual-stage airbag systems deploy based on collision severity: Stage 1 provides partial inflation, and Stage 2 provides full deployment for maximum protection.

A 0-ohm resistance typically indicates a short circuit in the inflator itself, the internal wiring of the clock spring (spiral cable), or a wiring harness short to ground.

This fault causes the SRS system to identify a risk of unintended Stage 2 deployment.

Consequently, the system illuminates the airbag warning light and may disable the entire driver-side front airbag, severely compromising occupant protection during a collision.

3
Cases Logged
Real-World Cases
BYD DTC AI Analysis

BYD Qin EV450 clock spring internal short circuit causing B1784-00

✓
2018 Qin EV450, 62,000 km. Airbag warning light on. DTCs B1784-00 and B1783-00 (first-stage resistance abnormal). Disassembly found the clock spring damaged during a previous steering wheel modification. Measuring continuity from top to bottom showed 0.3Ω between second-stage circuit pins (normal: continuity with measurable resistance). Replaced with OEM clock spring (part number: BYD-3658310-XX). Second-stage circuit resistance restored to 2.4Ω. Cleared codes; system normal.
BYD DTC AI Analysis

Qin 100 airbag connector corroded and short-circuited after water wading

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2017 BYD Qin 100. After driving through water, instrument cluster displayed "Check SRS System". Scanning revealed active DTC B1784-00. Removed driver airbag; connector (grey 2-pin) had significant water staining and green corrosion. Cleaned and dried terminals, but still measured 0Ω — igniter internally short-circuited. Replaced driver airbag module (new mounting bolts required) and applied anti-corrosion treatment to wiring harness connector. Fault resolved.
BYD DTC AI Analysis

Aftermarket steering wheel caused wiring harness to chafe and short circuit.

✓
A 2017 BYD Qin 80 showed an airbag warning light after the owner installed a third-party steering wheel cover and modifications. Diagnostics revealed intermittent DTC B1784-00. Inspection found the SRS wiring harness had not been secured correctly during the modification; it was rubbing against a metal bracket inside the steering column, wearing through the insulation and causing an intermittent short to ground. Repaired the damaged wiring with high-temperature tape and corrugated tubing, then re-routed and secured the harness to factory specifications with adequate slack for steering wheel rotation. The fault did not recur.
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.