Head Lamp Relay Coil Short to Battery
The headlamp relay coil is receiving too much voltage directly from the battery instead of being controlled properly by the ECU, like a light switch that's stuck in the 'on' position from a power surge. This electrical short prevents normal headlamp operation and can damage the relay or wiring.
The ECU monitors the voltage across the headlamp relay coil during normal switching cycles. It expects the coil to receive controlled voltage pulses from the relay driver circuit, typically 12V when activated and 0V when deactivated. A direct short to battery means the ECU detects constant high voltage instead of controlled switching, triggering the fault.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| Relay Coil Voltage | 0V (off) to 12V (on) with controlled switching | Continuous 12V+ voltage detected on coil |
| Coil Current Draw | 50-150mA during activation | Excessive current or no response to ECU commands |
Code B2249 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, B2249 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.