Illuminated Entry Input Open Circuit
The illuminated entry (dome light) circuit has an open wire or bad connection, so the ECU can't detect when it should be on. It's like a light switch with a broken wire—the switch works, but power never reaches the bulb.
The body control module monitors voltage on the illuminated entry circuit. It expects a signal transition when a door opens or the switch is pressed. An open circuit creates a floating or permanently high voltage state that the ECU cannot recognize as a valid input.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| Circuit Voltage | 0V (closed/active) to 12V (open/inactive) with clean transitions | No voltage change detected or stuck at high impedance |
| Signal Response Time | Voltage transition within 500ms of door opening | No transition detected or timeout exceeded |
Code B1608 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, B1608 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.