B1739 — Mirror Driver Horizontal Switch Circuit Short To Battery

The diagnostic trouble code B1739 indicates a problem within the circuit of the driver’s side mirror horizontal adjustment switch. Specifically, it points to a short circuit to the battery, meaning that the switch’s wiring or internal components may be damaged or incorrectly wired, causing a low-resistance path directly to the power source. This can potentially cause electrical issues or component malfunctions.

Note that labelling conventions for this code may vary between vehicle manufacturers, and some OEMs may have different code formats or descriptions for similar issues.

Fast Facts

System affected: Mirror adjustment circuit

Severity: Moderate — potential for electrical damage but typically not dangerous

Main symptoms: Mirror control issues, warning lights, possible fuse blowout

Driveability: Limited — may affect vehicle function but often not immobilising

Manufacturer variations for trouble code B1739

While the core meaning of B1739 remains consistent across different brands, the specific labels or descriptions used by OEMs can differ. Here are some known variations:

Ford: B1739 — “Mirror Driver Horizontal Switch Circuit Short To Battery”
Volkswagen / Audi / SEAT / Škoda: May use labels indicating issues with the “Driver Side Mirror Adjustment Switch Circuit”
BMW: Similar fault codes might reference “Mirror Adjustment Switch Circuit – Short to Battery”
Toyota / Honda / Nissan: Might use specific codes referencing mirror switch electrical circuit faults

What does trouble code B1739 mean?

B1739 is an OBD-II trouble code that specifically relates to issues with the electrical circuit of the driver’s side (left side) mirror horizontal adjustment switch. The onboard diagnostic system (ECU — Engine Control Unit) continuously monitors various electrical circuits, looking for anomalies like shorts or open circuits.

This particular fault indicates that the ECU has detected a short circuit to the battery within the circuitry that controls the horizontal movement of the mirror. Typically, the code is triggered when the switch’s wiring or internal components cause an unintended low-resistance connection to the vehicle’s positive terminal, which can lead to excessive current flow and potential component damage.

The trigger scenario often involves a short circuit or wiring fault in the door mirror wiring loom, the switch itself, or connectors that have become damaged or corroded over time. The problem might also arise after repairs, modifications, or if debris causes an internal short circuit.

Severity and risks of trouble code B1739

The presence of B1739 suggests a moderate level of risk. While the issue generally does not cause immediate vehicle immobilisation or pose a safety hazard, it can lead to additional electrical problems if left unresolved. For example, a short circuit can cause fuse blowouts or damage to the switch or related wiring, potentially affecting other electrical systems in the vehicle.

Can the vehicle be driven? In most cases, yes — but it’s advisable to address the issue promptly to prevent further electrical damage. Continued operation without repair could lead to more serious issues, such as wiring melting or blown fuses.

Symptoms of trouble code B1739

The symptoms associated with B1739 can vary depending on the extent of the electrical issue. Common signs include:

Failure or unresponsiveness of the mirror adjustment functions on the driver’s side.
Warning lights on the dash, such as the electrical system or mirror-related alerts.
Fuses burning out in the mirror circuit or related electrical systems.
An intermittent or no response when attempting to control the mirror adjustment switch.
Potentially, a burning smell or overheating from the door panel if the short circuit is severe.

Most likely causes of trouble code B1739

Understanding the possible origins of this fault helps guide efficient diagnosis and repair. Here are the most common causes, ranked from most to least likely:

Damaged or shorted wiring loom within the door, especially in the mirror or switch area. Damage from rough handling, door panel removal, or age-related wear can cause insulation to break down and create a short.
Faulty or internal switch inside the mirror control, which may have developed a short circuit or internal component failure.
Corroded or loose connectors within the wiring harness or at the switch connection point, leading to poor contact and potential short circuits.
Overvoltage or power surges that may have damaged the wiring or switch components.
External damage or impact causing wiring insulation to crack or wires to cross, especially in accident aftermath.

How to diagnose trouble code B1739

Diagnosing B1739 involves careful inspection of electrical components, wiring, and operational tests. Here’s a generic approach suitable for most vehicles:

Visually inspect the door mirror wiring harness and connectors for signs of damage, corrosion, or disconnection. Check for broken wires, burnt insulation, or melted parts.
Test the circuit continuity using a multimeter to verify if there is any short circuit to the battery or open circuits in the wiring loom.
Inspect the switch itself for internal damage or signs of malfunction. If possible, remove the switch for testing or replacement.
Use live data or scan tool to observe how the circuit behaves when operating the mirror switch. Look for abnormal readings or circuit errors.
Check fuse status related to mirror control circuits, replacing any blown fuses as needed.
If necessary, perform wiring repairs, such as reconnecting, splicing, or replacing damaged sections, following manufacturer specifications.

Possible repairs for trouble code B1739

Based on the identified cause, several repair options are available. Some repairs are straightforward, while others require professional intervention:

Replace damaged wiring or connectors: Suitable for minor insulation damage or corrosion, typically a basic repair that can often be DIY if familiar with automotive wiring.
Replace the mirror adjustment switch: Usually a straightforward procedure, but recommended to be performed by a professional for proper calibration and wiring checks.
Repair or replace wiring harness sections: For extensive damage, involving splicing and crimping, best handled by experienced technicians.
Check and fix fuse issues: Replacing blown fuses, which is a quick and simple fix but only addresses symptoms, not underlying causes.

Vehicles commonly associated with trouble code B1739 in Europe

While the presence of B1739 can appear across various vehicle brands, certain models and manufacturer groups are more frequently affected due to specific wiring designs or component placement. Notable examples include:

Ford — Focus, Fiesta, and Mondeo models
Volkswagen Group — Golf, Polo, Passat, A3, Octavia
BMW — Series 3, 5, and 7 with mirror control systems
Toyota — Corolla, Yaris, RAV4 (particularly in models with electronic mirror adjustment)
Nissan — Qashqai, Juke, Altima

Frequent mistakes with trouble code B1739

Diagnosing and repairing B1739 can be complicated by common errors. Being aware of these pitfalls helps improve repair accuracy and avoid unnecessary replacements:

Assuming the switch itself is always faulty without inspecting wiring or connectors first.
Ignoring corrosion or damage in wiring harnesses that may cause intermittent faults.
Replacing components without confirming electrical faults, leading to repeated faults or misdiagnosis.
Overlooking fuse status as a cause for circuit malfunction.
Failing to clear the fault after repairs to verify if the issue is truly resolved, which can leave the fault code active.

FAQ — trouble code B1739

Can this code disappear on its own?

Typically, no. B1739 usually indicates a hardware fault that won’t resolve without intervention. However, some minor wiring issues might temporarily cause the code to clear if conditions change or wires temporarily shift, but persistent problems will usually cause the code to return.

Can I keep driving?

In most cases, yes — but it’s recommended to get the issue diagnosed and repaired promptly. Ignoring it may lead to electrical system damage or malfunction of the mirror adjustment, which can affect driving comfort and safety.

Why does the code return after clearing?

The fault persists because the underlying problem—such as damaged wiring, a faulty switch, or corrosion—has not been fixed. Clearing the code only resets the ECU’s stored fault data temporarily; the issue reappears when the fault condition is re-triggered.