Code
BF00
DS
B — Body
Microphone input fault: Short circuit to earth
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UK: 1
EN: 0
RU: 2
AI status
Completed
Completed
100%
Causes
- Damaged microphone element or internal short
- Damaged/deteriorated wiring harness with insulation chafing to chassis or ground
- Corroded or contaminated connector causing a short to ground
- Water ingress in microphone or connector (moisture bridging to ground)
- Faulty amplifier/input stage in the head unit or hands-free control module
- Incorrectly fitted or damaged aftermarket audio device or adapter
Symptoms
- Microphone not working for phone calls or voice commands
- Hands-free/voice recognition error messages or no voice input detected
- Intermittent loss of microphone function, often correlated with door closure or vibration
- DTC BF00 stored in infotainment/telephone module diagnostic memory
What to check
- Read stored faults and freeze-frame data from infotainment or hands-free module
- Inspect microphone connector(s) and wiring harness visually for damage, corrosion, bent pins or water ingress
- With ignition ON, back-probe microphone signal and ground at the connector and check voltages with a digital multimeter
- Check continuity between microphone signal pin and chassis ground (looking for low resistance indicating a short)
- Disconnect the microphone and cycle ignition to see if fault clears or changes
- Wiggle test the harness while monitoring live data/voltage to reproduce the fault
Signal parameters
- Expected microphone bias voltage (at microphone signal pin with mic connected and ignition/accessory ON): typically a few volts (commonly ~2–5 V) — should NOT be 0 V or hard-grounded
- DC resistance from microphone signal pin to chassis ground when circuit healthy: high (typically >10 kΩ) — short-to-ground will show near 0 Ω
- AC audio signal: small mV-level audio waveform when speaking into microphone (observable with an oscilloscope)
- If microphone disconnected, bias voltage should be present at head unit input (if preamp powered) — absence indicates upstream power/input fault
Diagnostic algorithm
- Read and record BF00 fault details, occurrence count and freeze frame data from the telephone/infotainment module.
- Consult wiring diagram to locate microphone(s), connectors, ground points and the module input pin used by the vehicle.
- Perform a visual inspection of microphone(s) and harness for damage, corrosion, water, or pin intrusion. Repair obvious damage.
- With ignition ON, measure DC voltage at the microphone connector signal pin relative to chassis ground. Note voltage with microphone connected and then with it disconnected.
- Measure resistance/continuity between the microphone signal pin and chassis ground with ignition OFF. A low resistance (< a few ohms) indicates a short to ground.
- If a short is present, isolate sections of the harness: disconnect at intermediate connectors/modules and repeat continuity check to locate the shorted segment.
- Back-probe or use an oscilloscope on the microphone input while speaking into microphone to confirm presence/absence of AC audio and to check for noise or low-level signal.
- Perform a wiggle test along harness routing while monitoring voltage/continuity to reproduce intermittent faults.
- If wiring and connectors check good, test or swap the microphone (or head unit input/preamp) with a known-good unit if available to determine whether microphone or module is faulty.
- Repair wiring: repair/replace damaged sections, clean or replace corroded connectors, reseal against moisture, or replace microphone/module as required.
- Clear codes, re-test system operations and perform a function test with calls/voice commands to confirm repair. Re-scan for codes and road test if necessary.
Likely causes
- Connector pin pushed out and touching chassis or ground terminal
- Wiring abrasion where harness rubs against body panel or bracket
- Moisture or corrosion in the microphone connector
- Failed microphone preamp inside head unit or external microphone assembly
Fault status
Status
Microphone input: short to earth detected on microphone signal line. Fault stored in telephone/infotainment module.
Repair difficulty: Medium
Diagnostic time: 0.5-1.5 hours
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