AU
B1789-00

This DTC indicates a short-to-ground fault in the Stage 2 firing circuit of the dual-stage driver airbag — Seal 6 EV

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 Seal 6 EV indicates a high-severity short to ground in the Stage 2 driver airbag firing circuit. This can disable enhanced second-stage airbag deployment and turn on the airbag warning light. Common causes include damaged clock spring ribbon cable insulation 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.
5
Cases Logged
5
Causes
Likely Causes — Seal 6 EV
  • 1Damaged or broken insulation on the internal flat ribbon cable of 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 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.
  • 3The steering wheel-to-steering column wiring harness wears over time due to repeated steering wheel rotation, causing damaged insulation to contact the metal vehicle frame.
  • 4Airbag module squib internal insulation failure or internal short circuit (less common; usually occurs with abnormal airbag resistance)
  • 5SRS control unit (ACU) internal driver circuit fault or output stage breakdown, 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 across the airbag terminals directly.
  • 2
    Fault confirmation: Use the BYD VDS2000 or Launch X431 diagnostic tool to read the fault code. Confirm B1789-00 is a current fault (Active) and not a history fault. Record the resistance value in the freeze frame data (usually <1Ω).
  • 3
    Visual inspection: Inspect the airbag wiring harness connector (yellow marking) under the steering wheel for looseness, water ingress, oxidation, or bent pins. Inspect the clock spring 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 the following 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 isolates the short circuit to either 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 of the Stage 2 circuit (usually the yellow/black wire) from both terminals to the housing and between the terminals. Normal resistance to the housing is >1 MΩ. 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 the damage is severe, replace the instrument panel wiring harness or the engine compartment-to-cabin wiring harness.
  • 7
    Component replacement: If confirming an internal short circuit in the clock spring, replace the clock spring with one of the same part number (maintain the center position during installation); if confirming an internal short circuit in the airbag module, replace the driver airbag assembly.
  • 8
    System verification: Restore all connections, connect the battery, and use the diagnostic tool to clear the fault code. Perform 'SRS System Self-Diagnosis' and read the Stage 2 circuit resistance value (must be 1.5-3.5 Ω). Verify the airbag warning light turns off.
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

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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

✓
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 Seal 6 EV 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.B1737DTC B1737 indicates the Supplemental Restraint System (SRS) detected abnormal continuity between the right middle-row side airbag squib circuit (typically the second-row right seat side airbag or right curtain airbag) and the vehicle power supply (B+, battery positive). The SRS ECU monitors the airbag inflator resistance via an internal current source (normal resistance: 2.0–3.0 Ω). If the ECU detects the voltage across the inflator circuit remaining close to battery voltage (>5 V and approaching 12 V) instead of the expected low potential or floating state, it identifies a short to power. This fault prevents the airbag from deploying normally during a collision because the short circuit bypasses the firing current. In extreme cases, abnormal current can cause unintended deployment, posing a severe safety hazard.B173BDTC B173B indicates an abnormal electric A/C compressor speed feedback signal or a communication fault between the compressor controller and the motor. In BYD new energy models (e.g., Tang, Song, Qin, and Yuan series), this DTC belongs to the HVAC subsystem within the Body Control system and specifically involves the electric compressor closed-loop control circuit. The ECU sets this DTC when the compressor controller (IPM) fails to receive a valid pulse signal from the Hall speed sensor for more than 3 continuous seconds, or when the deviation between the detected actual speed and the target commanded speed exceeds the calibrated threshold (typically >500 rpm). This fault forces the A/C system into fail-safe mode and stops compressor operation. Symptoms include a complete lack of cooling, intermittent cooling, or a sharp decrease in cooling performance. The instrument cluster A/C warning lamp may also illuminate. Prolonged operation with this fault can degrade high-voltage system insulation or cause controller overcurrent damage.
Common problems reported for Seal 6 EV →Seal 6 EV 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.