Air Bag Crash Sensor #2 Feed/Return Circuit Failure
The airbag system's crash sensor #2 has an electrical connection problem, like a loose phone charger that won't deliver power. The ECU can't properly communicate with this sensor to detect crashes and deploy airbags when needed.
The ECU monitors the voltage signal and circuit resistance from crash sensor #2's power and ground lines. It expects stable voltage levels and low resistance; any open circuits, shorts, or excessive resistance triggers this fault. The sensor must respond within specific electrical parameters to indicate proper collision detection capability.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| Circuit Voltage | 5V nominal with <1Ω resistance | Open circuit, <0.5V, or >10kΩ resistance |
| Signal Continuity | Continuous path between sensor and ECU | Broken wire, corroded connector, or disconnected harness |
Code B1904 is a low-severity fault. Your vehicle is generally safe to drive to a workshop for diagnosis. However, do not ignore it indefinitely — low-severity codes often indicate developing problems that become expensive if neglected. Book a diagnostic appointment within 2–4 weeks. If you notice any additional symptoms (rough running, power loss, unusual smells), treat it as higher priority.
Once the fault is repaired, B1904 can be cleared using any OBD-II scanner. Connect the scanner, navigate to "Clear Codes" or "Erase DTCs," and confirm. The check engine light turns off immediately.
The code will return if the root cause was not actually fixed. The ECM re-detects the fault within 1–3 drive cycles and sets the code again.