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AU
B1789-00

This DTC indicates a short-to-ground fault in the Stage 2 firing circuit of the dual-stage driver airbag — Qin Plus

Safety System

This DTC indicates a short-to-ground fault in the Stage 2 firing circuit of the dual-stage driver airbag.

In modern airbag systems, the second stage usually deploys simultaneously with or after the first stage during a severe collision, providing greater inflation volume for enhanced protection.

A short to ground indicates damaged wire insulation or an internal connector fault in the circuit between the Airbag Control Unit (ACU) and the airbag squib.

This creates a low-resistance path (typically <1Ω) between the circuit and the vehicle body ground.

When the ACU detects an abnormal drop in circuit resistance, it immediately disables the Stage 2 airbag circuit and illuminates the airbag warning lamp to prevent accidental deployment or insufficient trigger energy.

If a severe collision occurs in this state, the driver receives only first-stage airbag protection.

The second-stage enhanced deployment function fails, but the first-stage airbag typically continues to operate normally.

5
Cases Logged
Real-World Cases
BYD DTC AI Analysis

BYD Qin EV450: Internal short in clock spring caused DTC B1789-00

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2018 Qin EV450 with 80,000 km: dash showed "Check SRS System". Scanner read current code B1789-00. Inspection found the fault occurred more frequently at full steering lock. Disconnecting the clock spring lower end and measuring the upper end to ground showed 0.2Ω, confirming internal Stage 2 circuit insulation had worn through and shorted to the metal housing. Replaced the clock spring (part number: K9-5820200). Circuit resistance returned to 2.4Ω and the fault cleared.
BYD DTC AI Analysis

Connector corrosion after water wading caused short to ground

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2017 BYD Qin 100. SRS warning light stayed on after the vehicle drove through water. Fault code B1789-00. Inspection found water inside the yellow airbag connector under the steering wheel, with pins oxidised green. Cleaned the connector with electronic cleaner, applied conductive grease and dried. Resistance to ground restored to >10MΩ. Cleared fault codes; system returned to normal. Check door seals and AC drain hose to prevent further water ingress.
BYD DTC AI Analysis

Aftermarket steering wheel installation pulled and chafed the wiring harness

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The customer fitted an aftermarket racing steering wheel and the B1789-00 fault appeared one week later. Inspection revealed the installer had not used an adapter harness. The modification had pulled the original clock spring to airbag wiring too tight, causing it to chafe against the steering column metal edge when the wheel turned. The damaged insulation caused the copper wires to short to ground. Repaired the damaged harness with high-temperature abrasion-resistant sleeving and refitted the factory steering wheel to clear the fault. Reminder: Aftermarket steering wheels require a compatible clock spring or airbag eliminator.
BYD DTC AI Analysis

False internal short circuit detection in airbag module

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A Qin EV300 repeatedly set DTC B1789-00. The clock spring and wiring harness were replaced, but the fault persisted. Further inspection revealed an internal short to ground in the driver airbag assembly Stage 2 igniter. Resistance from airbag connector Pins 3 and 4 (Stage 2 circuit) to the airbag housing measured 0Ω. Replacing the driver airbag assembly completely resolved the fault. Such cases are rare and usually indicate prior minor collision damage or improper airbag removal.
BYD DTC AI Analysis

Dashboard wiring harness retaining clip detached and worn

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B1789-00 appeared after accident repairs. Inspection revealed the repairer had not secured the SRS wiring harness to the factory mounting points when refitting the dashboard, allowing the harness to chafe against the metal dashboard bracket over bumps. The friction wore through the insulation and caused a short to ground. The technician rerouted the harness, secured it with OEM cable ties to the designated clips, wrapped the damaged section with insulation tape, and cleared the fault. SRS wiring must follow the factory routing exactly and maintain safe clearance from sharp edges.
Other Qin Plus 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.