B1899 — Microphone Input Signal Circuit Open

B1899 — Microphone Input Signal Circuit Open. A fault in the body electrical system. The car is usually drivable while you plan the repair. Typical causes: faulty switch, motor or actuator of the affected system, corroded or loose connectors, damaged wiring in door jambs or wet areas.

body electrical

Is it safe to drive?

Short-term driving is OK Usually safe to drive — body codes rarely affect drivability. Exceptions: exterior lighting and wipers in bad weather, and central locking faults that can leave the car unsecured.

How to diagnose with an OBD scanner

Read the code and freeze frame Connect an OBD2 scanner, confirm B1899 is stored, and save the freeze frame data — it shows engine conditions when the fault was detected.
Check for companion codes and TSBs Related codes often reveal the real root cause. Also check manufacturer technical service bulletins (TSB) for your make and model — many B0xxx issues have factory fixes or software updates. Search by VIN on the manufacturer site or nhtsa.gov.
Inspect wiring and connectors Visually inspect the wiring harness and connectors related to the body electrical system for damage, corrosion, chafing or poor contact.
Subsystem check Do a continuity test end-to-end on the microphone input signal circuit and wiggle the harness while measuring — intermittent opens show up as fluctuating readings.
Subsystem check Operate the affected function while watching its switch and motor PIDs in live data.
Subsystem check Inspect connectors and wiring at flex points (door jambs, tailgate hinges) — wires break there first.
Verify the repair Clear the code, complete a full drive cycle including the conditions from the freeze frame, and confirm B1899 does not return.

Approximate repair cost

Repair cost depends on which component actually failed. Typical scenarios for B1899 (parts and labor, USD, independent shop rates): BCM repair or replacement: $300–$900; Replace the switch or actuator: $120–$450; Repair wiring or connectors: $80–$250. Overall, fixing B1899 usually costs between $80 and $900. An accurate diagnosis before buying parts saves money — the most expensive scenario is rarely the first one to check.

Common questions

What is the most common cause of B1899?

The most common causes are: faulty switch, motor or actuator of the affected system, corroded or loose connectors, damaged wiring in door jambs or wet areas.

Will B1899 clear itself?

Sometimes B1899 clears after a few drive cycles if the fault was intermittent — for example a loose connector or a tank of bad fuel. The underlying cause usually remains, so the code tends to return. Clear it once; if it comes back, diagnose rather than erase it repeatedly.

What does OBD2 code B1899 mean?

How do I diagnose B1899 myself?

Start with a scan: confirm B1899, save the freeze frame and note any companion codes. Then inspect the wiring and connectors related to the microphone input signal, and verify the suspect component against live data before buying parts.

What are the symptoms of B1899?

Drivers most often notice: the affected function (locks, windows, lighting, wipers) works intermittently or not at all, no impact on engine operation in most cases, warning light on the dashboard.

When your scan tool pulls a B1899 code, the vehicle's computer is reporting an electrical fault within the body control system: specifically, an open circuit condition in the microphone input signal circuit. This falls under the B-series category that covers body and chassis electrical problems, as opposed to drivetrain or emissions-related faults.

An "open circuit" simply means that the electrical pathway the module uses to communicate with the microphone input has been interrupted somewhere along its route. Current cannot flow through a broken or disconnected path, so the module detects this absence and logs the fault after it observes the abnormal condition for the required number of drive cycles. Common culprits include severed wires, loose or corroded connectors, blown fuses, or a component that has failed internally.

The body control module continuously monitors this circuit while the vehicle operates. When sensor readings fall outside acceptable parameters, the module stores B1899 and illuminates the warning indicator. The freeze frame data captured alongside the code provides a snapshot of engine operating conditions at the exact moment the fault occurred—RPM, engine load, coolant temperature, and vehicle speed. This information proves invaluable during diagnosis because it tells you precisely what conditions triggered the code.

Common Symptoms of B1899

The specific function controlled by the affected circuit—such as power locks, windows, interior lighting, or windshield wipers—operates intermittently or stops functioning entirely
The instrument cluster displays an illuminated warning light, signaling that a body system fault has been detected
In most instances, engine performance, fuel economy, and drivability remain unaffected
The microphone or voice command system may fail to respond when prompted
Audio feedback or hands-free communication features become unavailable
Some vehicles may exhibit multiple related B-series codes alongside B1899

What Causes B1899?

A blown fuse that provides power to the microphone input signal circuit
A disconnected connector, backed-out terminal pin, or significant corrosion buildup at electrical junctions
A broken or severed wire within the microphone input signal harness
Complete internal failure of the microphone input component itself
Faulty body control module unable to process input signals correctly
A failed relay that controls power delivery to the affected circuit
Loose or corroded wiring connections at junctions throughout the harness
Wiring damage at high-flex areas such as door jambs, tailgate hinges, or other pivot points exposed to moisture

How to Diagnose B1899

Connect an OBD2 scanner and verify that B1899 is present in the stored codes. Record all freeze frame data—this information reveals exactly what engine conditions existed when the module first detected the fault.
Search for any manufacturer technical service bulletins specific to your make, model, and year. Many B-series codes have known factory defects or software updates that resolve the issue without physical repair. Check both the manufacturer website and NHTSA databases using your VIN.
Perform a thorough visual inspection of the wiring harness and connectors associated with the body electrical system. Look for damaged insulation, corrosion, broken strands, and any signs of water intrusion or overheating.
Using a digital multimeter, conduct a continuity test on the microphone input signal circuit from end to end. While monitoring readings, gently wiggle the harness—this technique often reveals intermittent opens that would otherwise go undetected.
Access live data parameters for the affected switch and motor while operating the system manually. Compare actual readings against expected values to confirm proper signal transmission.
Pay special attention to connector inspection at flex points where wires pass through door frames and body panels—these areas experience repetitive motion and are prone to fatigue failures.
Clear the code, then drive the vehicle through a complete drive cycle that recreates the conditions shown in the freeze frame data. Verify that B1899 does not reappear.

Repair Options for B1899

Address the least expensive and most common failure points before considering component replacement:

Wiring or connector repair: $80–$250 — Typically involves soldering broken wires, cleaning corrosion from terminals, or replacing damaged connectors
Switch or actuator replacement: $120–$450 — The faulty component is removed and replaced with a new or refurbished unit
Body control module repair or replacement: $300–$900 — May require module reprogramming or full replacement depending on the specific failure mode

How Much Does Fixing B1899 Cost?

Total repair expense varies based on which component triggered the code. At independent shop labor rates, expect the following ranges for parts and labor combined:

Wiring and connector repairs typically run $80 to $250 depending on accessibility and extent of damage
Switch or actuator replacement generally costs between $120 and $450 depending on the specific component and vehicle
Body control module work, including potential reprogramming, ranges from $300 to $900

Most B1899 repairs fall somewhere between $80 and $900. The critical point: perform accurate diagnosis before purchasing expensive parts. BCM replacement represents the costliest scenario and should be your last consideration after ruling out simpler issues like fuses, connectors, and wiring damage.

Can You Drive with B1899?

Generally safe to operate—the vast majority of body electrical codes do not impact engine operation or vehicle drivability. However, consider the specific function affected by the fault. If B1899 involves exterior lighting circuits, you lose visibility at night or in poor weather. Wiper motor faults create safety hazards during rain or snow. Central locking failures can leave your vehicle unsecured. Use your best judgment based on which system the code affects.