AU
B1789-00

This DTC indicates a short-to-ground fault in the Stage 2 firing circuit of the dual-stage driver airbag — Atto 3

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
5
Causes
Likely Causes — Atto 3
  • 1Damaged or broken insulation on the internal flat ribbon cable of the clock spring (spiral cable) causes the wire core to short to the steering wheel metal frame. This is the most common root cause of this fault.
  • 2Driver airbag connector (usually located beneath the steering wheel or on the back of the airbag) pins bent or backed out, or poor connector sealing causing water ingress and corrosion, resulting in a short to ground.
  • 3The wiring harness between the steering wheel and the steering column wears over time due to repeated steering wheel rotation, damaging the insulation and contacting the metal vehicle frame.
  • 4Internal insulation failure or internal short circuit in the airbag module squib (less common; typically presents with abnormal airbag resistance)
  • 5SRS control unit (ACU) internal driver circuit fault or output stage breakdown, causing a false detection of a short to ground (confirm after ruling out wiring harness faults).
What To Do
  • 1
    Safety Preparation: Disconnect the 12V battery negative terminal and wait at least 90 seconds (120 seconds for some models) to allow the SRS capacitor to fully discharge. Never use a standard multimeter to measure directly across the airbag terminals.
  • 2
    Fault confirmation: Use a BYD VDS2000 or Launch X431 diagnostic tool to read the fault code. Confirm B1789-00 is a current fault (Active), not a historical fault. Record the resistance value in the freeze frame data (usually displays <1Ω).
  • 3
    Visual inspection: Check the airbag wiring harness connector (yellow marking) under the steering wheel for looseness, water ingress, oxidation, or bent pins. Inspect the clock spring exterior for burn marks or physical damage.
  • 4
    Segmented measurement: Disconnect the lower clock spring connector and use a high-impedance multimeter (>10MΩ input impedance) to measure separately: ① resistance to ground at the upper end of the clock spring (to the airbag); ② resistance to ground at the lower end of the clock spring (to the ECU). This determines whether the short circuit is on the steering wheel side or the body wiring harness side.
  • 5
    Clock spring test: Remove the steering wheel (use the special puller; do not use impact tools). Remove the clock spring. Measure the resistance of the Stage 2 circuit (usually the yellow/black wire) from both terminals to the housing, and between the two terminals. Resistance to the housing should be >1MΩ, and continuity resistance should be approximately 2-3Ω.
  • 6
    Wiring harness repair: If the wiring harness is damaged, repair it with high-temperature tape and install an abrasion-resistant sleeve. If the damage is severe, replace the instrument panel wiring harness or the engine compartment-to-cabin wiring harness.
  • 7
    Component replacement: If an internal short circuit in the clock spring is confirmed, replace the clock spring with one of the same part number (maintain the center position during installation); if an internal short circuit in the airbag module is confirmed, replace the driver airbag assembly.
  • 8
    System verification: Restore all connections and connect the battery. Use the diagnostic tool to clear the fault code. Perform "SRS System Self-diagnosis". Read the Stage 2 circuit resistance value; it should be 1.5-3.5 Ω. Confirm the airbag warning light turns off normally.
Real-World Cases
BYD DTC AI Analysis

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

✓
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

✓
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

✓
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

✓
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

✓
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 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: Official This information is for reference only. Always consult a qualified technician for diagnosis and repair. Do not attempt high-voltage system repairs yourself.