AU
B1789-00

This DTC indicates a short-to-ground fault in the Stage 2 firing circuit of the dual-stage driver airbag — Atto 8

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.

The B1789-00 fault code on the Atto 8 indicates a high-severity short-to-ground fault in the Stage 2 firing circuit of the driver airbag. This can disable the second-stage airbag deployment and turn on the airbag warning light. Common causes include damaged clock spring wiring or corroded/bent driver airbag connector pins. The recommended fix is to visit an authorised dealer for diagnosis and repair. Typical repair cost data is available.
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Cases Logged
5
Causes
Likely Causes — Atto 8
  • 1Damaged or broken insulation on the internal flat ribbon cable in the clock spring (spiral cable) causes the conductor to short to the steering wheel metal frame. This is the most common root cause of this fault.
  • 2Bent or backed-out pins at the driver's airbag connector (usually located under the steering wheel or on the back of the airbag), or poor connector sealing causing water ingress and corrosion, resulting in a short to ground.
  • 3Repeated steering wheel rotation wears the wiring harness between the steering wheel and the steering column over time, causing the damaged insulation to contact the metal vehicle frame.
  • 4Airbag module squib insulation failure or internal short circuit (less common, usually occurs with abnormal airbag resistance)
  • 5Internal driver circuit fault or output stage breakdown in the SRS control unit (ACU) causing a false short-to-ground detection (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 fully discharge the SRS capacitor. Never use a standard multimeter to measure directly across the airbag terminals.
  • 2
    Fault Confirmation: Use the BYD VDS2000 or Launch X431 diagnostic tool to read the fault code. Verify B1789-00 is a current fault (Active), not a historical fault. Record the resistance value in the freeze frame data (usually displaying <1Ω).
  • 3
    Visual inspection: Check the airbag wiring harness connector under the steering wheel (yellow marking) for looseness, water ingress, oxidation, or bent pins. Inspect the clock spring exterior for burn marks or physical damage.
  • 4
    Sectional measurement: Disconnect the lower clock spring connector. Use a high-impedance multimeter (>10MΩ input impedance) to measure separately: ① resistance to ground at the upper end of the clock spring (to airbag); ② resistance to ground at the lower end of the clock spring (to 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 using the special puller (do not use impact tools). Remove the clock spring. Measure the resistance from both Stage 2 circuit terminals (usually the yellow/black wire) to the housing, and between the terminals. Normal resistance is >1 MΩ and continuity resistance is approximately 2-3 Ω.
  • 6
    Wiring harness repair: If the wiring harness is damaged, repair it with high-temperature tape and install an abrasion-resistant sleeve. If severely damaged, replace the instrument panel wiring harness or the engine compartment-to-cabin wiring harness.
  • 7
    Component replacement: If the clock spring has an internal short circuit, replace the clock spring with the same part number (keep it centered during installation); if the airbag module has an internal short circuit, 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 the 'SRS System Self-Diagnosis'. Read the Stage 2 circuit resistance value; it should be within 1.5-3.5Ω. 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 8 Fault Codes
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.B110A02DTC B110A02 indicates the thermal management master control unit (HVAC ECU) or body control module (BCM) failed to receive valid CAN data frames from the PM2.5 air quality sensor over consecutive communication cycles (typically 500ms per cycle). The sensor typically mounts at the HVAC unit air inlet or behind the glove box and transmits real-time particulate concentration data (unit: μg/m³) to the HVAC controller via the CAN bus. The fault is essentially a communication link layer timeout. Potential causes include physical layer wiring faults, sensor power supply failures, sensor internal MCU lockup, or CAN network topology damage. Although this non-critical fault does not directly affect driving safety, it disables the intelligent air purification strategy and the automatic fresh air/recirculation switching function. In extreme cases, it triggers a thermal management system degraded mode, limiting compressor power or fixing the air flap position.B110B07This fault code indicates abnormal operation of the internal air pump (sampling pump) in the PM2.5 air quality detection module. The PM2.5 detector uses the laser scattering principle to measure particulate concentration and requires a built-in air pump to draw ambient air into the detection chamber at a constant flow rate. The ECU sets this code when it detects an open or short in the air pump drive circuit, abnormal current (stall or free-running), or abnormal speed feedback. This fault causes the automatic air conditioning system to lose air quality sensing capability, preventing automatic switching between fresh air and recirculation modes. The instrument cluster air quality display may show '--' or a fixed value, but the fault does not affect the vehicle powertrain or basic air conditioning cooling and heating functions.B173CDTC B173C indicates the Supplemental Restraint System (SRS) detects the Right Second Row Side Airbag squib circuit resistance exceeds the calibrated threshold (typically >4.5Ω). This fault is an active diagnostic result of the SRS system, indicating a high-resistance condition in the circuit between the Airbag Control Unit (ACU) and the airbag module. Causes for excessive resistance include increased contact resistance, a partially broken wiring harness, terminal oxidation, or an aging squib wire inside the airbag module. This fault causes the system to mark the airbag circuit as 'unreliable', meaning the airbag may fail to deploy during a collision. The fault typically illuminates the instrument cluster airbag warning light (SRS light) continuously, and some models also sound a warning buzzer.
Common problems reported for Atto 8 →Atto 8 overview →
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.