Microphone Input Signal Circuit Open
The microphone that picks up sound input for your vehicle's voice command or hands-free system has a broken wire or loose connection, like a disconnected microphone cord. The ECU can't detect any signal coming from it.
The ECU monitors the microphone input circuit for a valid voltage signal, typically a variable signal indicating audio input levels. When the circuit is open (broken or disconnected), the ECU receives zero or no signal instead of the expected fluctuating voltage pattern.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| Microphone Signal Voltage | 0.5V - 4.5V with audio input variation | 0V constant or no signal detected |
| Circuit Continuity | Circuit resistance under 10 ohms | Open circuit, infinite resistance |
Code B1899 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, B1899 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.