B1899: Microphone Input Circuit Open
The B1899 code indicates that the vehicle's control module has detected an open circuit in the microphone input signal. This microphone is part of the hands-free system or communication module (such as Ford's SYNC), and its purpose is to capture the driver's voice for phone calls or voice commands. An open circuit means there is a break in electrical continuity between the microphone and the receiving module, preventing the audio signal from reaching it properly. Diagnosis should focus on checking the wiring harness, connectors, and the microphone itself. Always consult the specific vehicle wiring diagram, as microphone and module locations vary by model and year. Per SAE J2012, this is a body code (B) affecting comfort and convenience systems.
1. Commonly Affected Makes
2. Most Common Causes
- Microphone disconnected or connector corroded
- Microphone wiring cut, broken, or with bent pins
- Harness damaged by friction near steering column or rearview mirror
- Internal microphone short or open circuit
- Communication module (APIM) with faulty audio input port
- Control module connector loose or moisture-contaminated
3. Symptoms You Will Notice
- Inoperative hands-free calling
- Voice commands not recognized
4. Step-by-Step Diagnosis
Check for technical service bulletins (TSBs) related to the microphone circuit.
Visually inspect the microphone connector and wiring for damage, corrosion, or loose pins.
Test microphone continuity and resistance using a multimeter; compare to specifications.
Verify power and ground at the microphone connector.
Inspect the communication module (APIM) connector for bent pins or moisture.
If all else is good, suspect a faulty microphone or APIM module.
5. Frequently Asked Questions
Is it safe to drive?▼
Yes, the vehicle is safe to drive. This code only affects hands-free calling and voice command functions.
How much does it cost to fix?▼
Repair costs typically range from $100 to $400, depending on whether the issue is a simple connector fix or requires replacing the microphone or APIM module.