Lamp Anti-Theft Indicator Circuit Failure
The anti-theft indicator lamp circuit isn't communicating properly with the body control module, similar to a warning light that's broken or disconnected. The vehicle's security system can't confirm the lamp is working to alert you of a theft attempt.
The body control module continuously monitors the anti-theft lamp circuit for proper voltage and ground continuity during self-diagnostic cycles. It expects the lamp to draw a specific current when commanded on, and flags a fault if voltage is absent, shorted, or open.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| Lamp circuit current draw | 0.15–0.5 A when commanded on | No current or >0.5 A (short condition) |
| Circuit voltage at module | 12–14 V supply, 0 V ground when off | Open circuit or constant short to ground |
Code B1603 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, B1603 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.