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.

The B1789-00 fault code on the Qin Plus indicates a short to ground in the Stage 2 firing circuit of the dual-stage driver airbag. This is a high-severity airbag fault because enhanced second-stage deployment may be disabled in a severe crash. Common causes include damaged clock spring ribbon cable insulation or faulty, corroded, or loose driver airbag connector pins. Visit an authorised dealer for diagnosis and repair. Typical repair cost data is available from 5 recorded cases.
5
Cases Logged
5
Causes
Likely Causes — Qin Plus
  • 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 in 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 wiring harness between the steering wheel and steering column wears over time due to repeated steering wheel rotation. Damaged insulation allows the harness to contact the metal vehicle frame.
  • 4Internal insulation failure or internal short circuit in the airbag module squib (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 ensure the SRS capacitor discharges completely. 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 (Active) fault, not a history fault. Record the resistance value in the freeze frame data (usually displays <1Ω).
  • 3
    Visual inspection: Check the airbag wiring harness connector (yellow marking) below the steering wheel for looseness, water ingress, oxidation, or bent pins. Check the clock spring 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 the following separately: ① resistance to ground at the upper clock spring (to the airbag); ② resistance to ground at the lower clock spring (to the ECU). This isolates the short circuit to either the steering wheel side or the body harness side.
  • 5
    Clock spring test: Remove the steering wheel (use a special puller; impact tools prohibited). Remove the clock spring. Measure the resistance from the Stage 2 circuit terminals (usually the yellow/black wire) to the housing, and between the terminals. Normal resistance is >1MΩ, and continuity resistance is 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 testing confirms an internal short circuit in the clock spring, replace it with a clock spring of the same part number (maintain the centered position during installation); if testing confirms 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 the 'SRS System Self-Diagnosis'. Read the Stage 2 circuit resistance value; it should be 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

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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

✓
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.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.B110BDTC B110B indicates a fault in the internal air pump (sampling pump) of the PM2.5 air quality detector. This pump draws cabin or outside air into the PM2.5 sensor detection chamber, enabling the laser scattering sensor to measure real-time particulate matter concentration. The air conditioning controller (or BCM) sets this DTC upon detecting an open or short circuit in the pump drive circuit, or abnormal current caused by a seized pump motor. This fault disables the "Green Clean" system, causes the instrument cluster air quality display to read abnormally or disappear, and disables the automatic fresh air/recirculation switching function. It does not affect the vehicle powertrain or core thermal management functions.B173A1ADTC B173A1A indicates the right middle-row side airbag (typically located on the side of the right second-row seat or inside the C-pillar trim panel) igniter circuit resistance measures 0 Ω. In the Supplemental Restraint System (SRS), normal airbag igniter resistance ranges between 2.0 and 5.0 Ω. A resistance of 0 Ω indicates a short to ground or a short between circuit wires, preventing the Airbag Control Unit (ACU) from establishing a normal monitoring circuit. This safety-critical fault prevents the airbag from deploying during a collision, continuously illuminates the instrument panel SRS warning lamp, and may force the entire airbag system into fail-safe mode.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 Qin Plus →Qin Plus 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.