Code
B1899
Other
B — Body
Microphone Input Signal Circuit Open
AI status
Completed
Completed
100%
Causes
- Broken or damaged microphone wiring (open conductor)
- Disconnected or corroded microphone connector or mating socket
- Failed microphone element or microphone assembly (open internal element)
- Improper or missing pin at the module connector (pulled out pin)
- Poor ground at related circuit (if microphone requires ground return)
- Faulty infotainment/body control module or internal input circuit failure
Symptoms
- No voice input to hands‑free phone or voice recognition
- Other occupants cannot hear driver during calls
- Infotainment displays microphone error or “mic not detected” message
- Voice commands not recognized or intermittent operation
What to check
- Retrieve and confirm the B1899 code and any related microphone or audio codes
- Perform a visual inspection of microphone, wiring harness, and connectors for damage, corrosion, or loose pins
- Wiggle test harness and mic while attempting a voice input to reproduce intermittent behavior
- Consult vehicle wiring diagram to locate microphone connector and module pins
- Backprobe microphone connector and control module connector while measuring voltages and continuity
Signal parameters
- Typical electret microphone bias voltage: approximately 2–5 V DC on the microphone signal/bias line (varies by vehicle; confirm service manual)
- Expected continuity: low resistance between microphone signal conductor and module input pin (open = very high resistance or infinite)
- Audio signal: small AC audio waveform (mV level) on signal line when speaking into the microphone
- If present, ground continuity should be near 0 Ω between microphone ground and vehicle ground
Diagnostic algorithm
- Confirm and record freeze frame data and related codes, then clear codes and attempt to re‑produce B1899
- Visually inspect microphone and wiring for obvious damage, moisture, or disconnected connectors
- Locate microphone connector and unplug; inspect for corrosion, bent or pulled pins and repair as needed
- Measure continuity between the microphone signal pin and the module input pin. An open indicates damaged wiring or connectors
- Backprobe the microphone connector with ignition on. Check for expected bias voltage on the signal/bias wire (see service manual). If no bias, trace back to module and check module output pin and fuse/power feed
- With connector connected, speak into the mic and measure AC waveform on signal line with an oscilloscope or high‑sensitivity AC meter — substitute a known good microphone if available
- If wiring and microphone check good, scan/inspect the module connector pins at the control unit; repair any pin damage or reinsert terminal
- If wiring and mic are good and module pin has correct bias but there is still no signal, consider replacing the microphone assembly. If replacement fails, suspect module input failure and consult service manual for module replacement or further module‑level tests
- After repair, clear codes and road/test to confirm the code does not return
Likely causes
- Disconnected or corroded microphone connector at headliner/door or module
- Broken wire between microphone and control module due to chafing or door/seat movement
- Failed microphone assembly (open element)
- Connector pin pushed out or bent at control module
Fault status
Status
Microphone input circuit open — no microphone signal detected by the control module.
Repair difficulty: Medium
Diagnostic time: 0.5-1.5 hours
Similar codes
Repair manuals
Brands with available manuals
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