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 — Atto 3

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.

The B1694-00 fault code on the Atto 3 indicates the airbag control unit has detected low operating voltage, typically below 9.0V–10.5V, which may prevent proper airbag deployment or trigger unintentional deployment. This medium-severity issue is commonly caused by a weak battery, charging system faults, or corroded ground connections. You should visit an authorised dealer for diagnosis and repair. Typical repair cost data is available.
3
Cases Logged
5
Causes
Likely Causes — Atto 3
  • 1Battery aging or depletion, or charging system fault: Battery voltage is below 11V, or DC-DC converter output voltage is unstable, causing a voltage drop during startup or under high-current loads.
  • 2Loose or oxidized ground point: Loose or corroded SRS ECU housing ground or G10/G36 connector ground points (G10-28, G10-35, G36-35), increasing circuit resistance (>1Ω).
  • 3Instrument panel power distribution box power supply fault: Abnormal output voltage at terminal G2C-3, or burnt IG1 main relay contacts or coil fault, 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 causing a false low voltage reading (rule out external circuits before confirming).
What To Do
  • 1
    Basic check: Measure battery static voltage (should be ≥12.4V) and starting/charging voltage (should be 13.5-14.5V). Check battery terminals for tightness and oxidation. Charge or replace battery if necessary.
  • 2
    Fuse check: Inspect the SRS system-related fuse (such as F2/17) in the instrument panel fuse box for a blown condition or poor contact. Measure the voltage drop across the fuse holder.
  • 3
    Ground point check: Disconnect the battery negative terminal. Check the bolt tightening torque of the SRS ECU housing ground and G10-28/G10-35 (or G36-35) ground points (normally 8-10 N·m). Clean off any oxidation layer. Measure the resistance between the ground point and the vehicle body (should be <1 Ω).
  • 4
    Power distribution box and relay check: Measure terminal G2C-3 voltage with the ignition ON (should be 11-14V). Remove the IG1 main relay (K2-1) and test: apply power to pins 1-2; pins 3-5 should show continuity (<10Ω). Disconnect power; pins 3-5 should be open (>10KΩ). 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 supply wire (e.g., G10-1, G36-36) (11-14V with ignition ON). Measure the ground wire resistance to ground (<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 matching 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 Atto 3 Fault Codes
P0AA6Hybrid Battery Voltage System Isolation FaultB1108For 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.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.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.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.
Common problems reported for Atto 3 →Atto 3 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.