AU
B1694-00

The SRS (airbag system) control unit records DTC B1694-00 when it detects its operating supply voltage falls below the calibrated threshold (typically 9 — Qin Plus

Safety System

The SRS (airbag system) control unit records DTC B1694-00 when it detects its operating supply voltage falls below the calibrated threshold (typically 9.0V-10.5V, depending on specific vehicle calibration).

This fault indicates a voltage drop in the airbag ECU constant power or IGN supply circuit, which may prevent the airbag system from deploying properly during a collision or cause unintentional deployment while driving.

This fault triggers a safety system degraded mode.

The ECU illuminates the airbag fault warning lamp and stores the fault code.

On some models, this condition also limits functions such as the seat belt pretensioners and airbag backup power supply.

3
Cases Logged
5
Causes
Likely Causes — Qin Plus
  • 1Battery aging, discharged battery, or charging system fault: Battery voltage is below 11 V, or generator output voltage is unstable, causing a voltage drop during startup or under high-current loads.
  • 2Ground point loose or oxidized: Loose or corroded SRS ECU housing ground or G10/G36 connector ground points (G10-28, G10-35, G36-35) causing increased circuit resistance (>1Ω).
  • 3Instrument panel distribution box power supply fault: Abnormal output voltage at terminal G2C-3, or burnt contacts or coil failure in the IG1 main relay, causing insufficient power supply in the ON position.
  • 4Poor contact at wiring harness connectors: Terminal back-out, oxidation, or water ingress at key connectors such as G10, G36, and G2C, or internal open or short circuit in the power wiring harness.
  • 5SRS ECU internal fault: Damaged ECU internal power management module causes a false low voltage reading (confirm after ruling out external circuits).
What To Do
  • 1
    Basic check: Measure the battery static voltage (should be ≥12.4V) and starting/charging voltage (should be 13.5-14.5V). Check the battery terminals for tightness and oxidation. Charge or replace the battery if necessary.
  • 2
    Fuse check: Inspect the SRS system-related fuse (such as F2/17) in the instrument panel distribution box for a blown element or poor contact. Measure the voltage drop across the fuse holder.
  • 3
    Ground point check: Disconnect the battery negative terminal, check the tightening torque of the SRS ECU housing ground and G10-28/G10-35 (or G36-35) ground point bolts (normally 8-10 N·m), clean the oxidation layer, and measure the resistance between the ground point and the vehicle body (should be <1Ω).
  • 4
    Power distribution box and relay inspection: Measure the ON-position voltage at terminal G2C-3 (should be 11-14 V). Remove and test the IG1 main relay (K2-1): Apply power to pins 1-2; pins 3-5 must show continuity (<10 Ω). Disconnect power; pins 3-5 must be open (>10 kΩ). If abnormal, replace the relay or power distribution box.
  • 5
    Wiring harness continuity test: Disconnect connectors G10/G36. Measure the voltage to ground of the harness-side power wire (e.g., G10-1, G36-36) (11-14V in ON position). Measure the resistance to ground of the ground wire (<1Ω). Measure the continuity resistance from the harness side to the power distribution box (<1Ω).
  • 6
    ECU replacement verification: If all above checks are normal, disconnect all loads and retain only the basic power supply. If the fault code persists, replace the airbag ECU (Note: Perform coding and system calibration after replacement).
Real-World Cases
BYD DTC AI Analysis

Qin EV450 airbag warning light stays on after starting (B1694-00)

✓
Symptoms: After starting the vehicle, the airbag warning light stayed on constantly. The diagnostic scanner retrieved code B1694-00 (Supply Voltage Low). Diagnostic Process: Measured battery voltage at 12.2V (low), but the charging system worked normally. Checked the G36 connector and found the G36-35 ground terminal loose. Measured resistance to ground at 3.2Ω (exceeded specification). Cleaned the ground point and tightened the connection, reducing resistance to 0.3Ω. Cleared the fault code and the system returned to normal. Resolution: Tightened the SRS system ground point. Advised the owner to check battery health (4 years old, replacement recommended).
Original source ↗
BYD DTC AI Analysis

BYD S6 intermittently logs B1694-00 fault

✓
Symptoms: Airbag light would intermittently come on while driving, then clear after stopping and restarting. Historical DTC B1694-00 stored. Diagnosis: Checked battery and alternator – both normal. Found slight burning on the IG1 main relay (K2-1) contacts in the instrument panel fuse box. Measured resistance between relay pins 3-5; it was unstable, sometimes exceeding 20Ω. Replaced the relay and road tested; voltage at terminal G2C-3 stayed stable and the fault did not recur. Fix: Replaced IG1 main relay; inspected fuse box base – no signs of burning.
Original source ↗
BYD DTC AI Analysis

E1 EV low voltage with multiple system faults

✓
Symptoms: E1 model instrument cluster displayed the airbag warning light and system fault light simultaneously. Scanned the SRS system, retrieved DTC B1694-00. Diagnosis: Inspection found an aftermarket dashcam fitted with non-standard power tapping causing voltage drop. Measured G10-1 terminal voltage dropped to 9.8V with headlights switched on. Restored factory wiring and separately checked the SRS power supply circuit. Found G2C-3 terminal pin backed out, causing poor contact. Solution: Repaired the backed-out terminal pin, eliminated the non-standard power tapping, and confirmed voltage stable above 12.5V under load.
Original source ↗
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: Official This information is for reference only. Always consult a qualified technician for diagnosis and repair. Do not attempt high-voltage system repairs yourself.