Seat Driver Occupied Switch Circuit Short To Ground
The driver's seat occupancy sensor is sending a constant "ground" signal to the ECU, like a stuck light switch that won't turn off. This tells the vehicle someone is always sitting in the driver's seat, even when it's empty.
The ECU monitors the driver occupancy switch voltage signal, which should toggle between high and low states as the seat is occupied or unoccupied. A short to ground forces the signal to remain low continuously, preventing the ECU from detecting seat status changes. The sensor circuit normally operates at 5V with pull-up resistors; a ground short collapses voltage to 0V.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| Seat Occupancy Voltage | 4.5-5.0V (empty), 0.2-0.8V (occupied) | Stuck at 0V or below 0.2V continuously |
| Signal Transition | Voltage toggles when seat state changes | No voltage change detected; remains shorted to ground |
Code B1518 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, B1518 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.