Code
B28D8
Generic
B — Body
Bluetooth Hands-Free Microphone Circuit Malfunction
AI status
Completed
Completed
100%
Causes
- Failed or damaged hands-free microphone element
- Open, short or intermittent wiring in the microphone harness
- Corroded, loose or contaminated connector pins
- Loss of microphone bias/power or poor ground
- Faulty Bluetooth/infotainment module or microphone input circuitry
- Software/firmware bug or incorrect configuration
Symptoms
- No audio transmitted from vehicle microphone during calls
- Low or distorted voice pickup on hands-free calls
- Intermittent microphone operation (works sometimes)
- Caller reports very low volume, static, clipping, or echo
- Bluetooth/phone hands-free may fall back to phone mic
What to check
- Read stored codes and freeze frame data with a diagnostic tool; record related codes
- Perform a visual inspection of microphone, mounts and harness for damage or water
- Inspect connectors for corrosion, bent pins, or loose terminals
- Wiggle test microphone harness and connectors while reproducing the symptom
- Verify microphone is selected and configured in the infotainment settings
- Check for relevant software or TSB updates for the infotainment/Bluetooth module
Signal parameters
- Microphone bias (DC) voltage: typically ~1.5–3.3 V (check vehicle-specific spec)
- DC resistance between mic signal and ground: varies by microphone type, typically 1 kΩ–10 kΩ
- Audio signal amplitude (speaking loud): tens to several hundred mV peak-to-peak at mic input
- Continuity: no open between microphone pin and module input (0 Ω to few ohms for short runs)
- Short checks: no low-resistance short to battery + or ground on the signal line
Diagnostic algorithm
- Capture and record the code(s) and related data with a scan tool; check for multiple occurrences or history.
- Verify microphone selection and Bluetooth/phone settings in the infotainment system; attempt a test call or system microphone test if available.
- Visually inspect microphone, bracket, harness, and connectors for signs of damage, water, or corrosion.
- With connector disconnected, inspect terminal condition and probe for proper bias voltage from the module at the harness side (compare to vehicle spec).
- Check continuity and for shorts between microphone pins and ground/12V using a multimeter (vehicle ignition off for resistance checks).
- With ignition and system powered, speak into the mic while measuring the AC audio signal on the mic input with an oscilloscope or AC-coupled multimeter; look for usable waveform and amplitude.
- Perform a wiggle test of harness and connectors while monitoring for changes in signal or DTC presence.
- If wiring and bias are correct but no audio, substitute a known-good microphone (or known-good module input) if available to isolate component failure.
- Check and apply any available infotainment/Bluetooth module software updates or reprogram the module if recommended by OEM procedures.
- Clear codes and retest after repairs; verify normal microphone operation with multiple test calls and drive conditions.
Likely causes
- Corroded or loose connector at microphone or module
- Broken or chafed wiring in the microphone harness (open/short to ground/12V)
- Failed microphone element
- Loss of microphone bias voltage from module
- Intermittent connection due to vibration or water ingress
Fault status
Status
Bluetooth hands-free microphone circuit malfunction detected — possible microphone, wiring, connector, or module fault.
Repair difficulty: Medium
Diagnostic time: 0.5-2.0 hours
Similar codes
Repair manuals
Brands with available manuals
7,808
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