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 — Seal U

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 Seal U indicates the airbag system control unit has detected low operating voltage, typically below 9–10.5 volts, which may prevent airbags from deploying in a crash or cause accidental deployment. Severity is medium. Common causes include a weak battery, charging system faults, or corroded ground connections at the SRS ECU. You should visit an authorised dealer for inspection and repair. Typical repair cost data is available based on three recorded cases.
3
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Battery aging, low charge, or charging system fault: battery voltage is below 11V, 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 ground connections at the SRS ECU housing and G10/G36 connectors (G10-28, G10-35, G36-35) increase circuit resistance (>1Ω).
  • 3Instrument panel power distribution box power supply fault: Abnormal output voltage at terminal G2C-3, burnt IG1 main relay contacts, or faulty coil, causing insufficient power supply in the ON position.
  • 4Poor wiring harness connector contact: 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.
  • 5Internal SRS ECU fault: A damaged ECU internal power management module causes a false low voltage report (rule out external circuits before confirming).
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: Check if the SRS-related fuses in the instrument panel distribution box (such as F2/17) are blown or have poor contact. Measure the voltage drop across the fuse holder.
  • 3
    Ground point check: Disconnect the negative battery terminal. Check the tightening torque of the ground bolts for the SRS ECU housing and G10-28/G10-35 (or G36-35) ground points (typically 8-10 N·m). Remove any oxidation. Measure the resistance between the ground points and the vehicle body (should be <1 Ω).
  • 4
    Power distribution box and relay inspection: Measure the ON-position voltage at terminal G2C-3 (should be 11-14V). Remove the IG1 main relay (K2-1) and test: apply power to pins 1-2; pins 3-5 should have continuity (<10Ω). Remove power; pins 3-5 should disconnect (>10KΩ). If abnormal, replace the relay or power distribution box.
  • 5
    Harness continuity test: Disconnect connectors G10/G36. Measure the voltage to ground of the harness-side power supply wires (e.g., G10-1, G36-36) (11-14 V in the ON position). Measure the resistance to ground of the ground wires (<1 Ω). Measure the continuity resistance from the harness side to the power distribution box (<1 Ω).
  • 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 Seal U Fault Codes
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.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.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.B173712DTC B173712 indicates a short to power in the firing circuit of the right second-row side airbag module in the Supplemental Restraint System (SRS). Specifically, the "right second-row side airbag" typically refers to the side impact airbag located in the right B-pillar or the side of the right seat. The "12" suffix indicates a circuit short to battery positive (B+). This fault causes the following conditions: 1) The airbag may fail to ignite and deploy during a collision, resulting in a loss of side impact protection. 2) In extreme cases, unintended triggering may cause accidental airbag deployment. 3) The SRS control unit detects abnormally high circuit voltage (typically above 4.5V) and enters fault protection mode. This may disable the entire airbag system and continuously illuminate the instrument cluster airbag warning light.
Common problems reported for Seal U →Seal U 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.