B1740 — Mirror Driver Horizontal Switch Circuit Short To Ground

The diagnostic trouble code B1740 indicates a **short circuit to ground** in the **horizontal adjustment switch circuit** of the **driver side mirror**. This sensor or switch is responsible for controlling the horizontal movement of the mirror, and when a short occurs, it disrupts normal operation. Please note that labels and coding can vary between different vehicle manufacturers.

Manufacturer variations for trouble code B1740

Different vehicle manufacturers may label or code this fault differently, especially since the **mirror adjustment switch circuits** are part of the **body control system**. While the underlying cause remains the same, the specific code or terminology used may vary.

• Volkswagen / Audi: 5F0 959 761 J
• Ford: B1740 (or similar body control module codes)
• Toyota: Often not specified as B1740 but related codes within the body ECU
• BMW: 61358380288 (body switching unit faults)

Always refer to the specific OEM diagnostic guides for exact labelings and code definitions relevant to your vehicle.

What does trouble code B1740 mean?

At its core, B1740 signals that the vehicle’s Electronic Control Unit (ECU) has detected an interruption or short circuit in the horizontal mirror adjustment switch circuit. Essentially, the ECU monitors the circuit for proper operation, and when it finds that the switch’s circuitry is **shorted to ground**, it triggers this fault code. This specific switch allows the driver to move the side mirror left or right with a button press.

This trigger typically occurs when there is an **internal wiring fault**, a **damaged switch**, or a **short-circuit in the wiring harness**. Usually, this code appears in the context of problems related to **mirror control functionality** but may also be accompanied by warning lights on the dash or in the vehicle’s information display system.

Severity and risks of trouble code B1740

The B1740 fault generally presents a **moderate** level of risk. While it **does not** directly affect the engine or critical safety systems, it can impair **manual adjustment of the side mirror**, which is essential for proper driving visibility. If the mirror cannot be adjusted correctly, it may lead to blind spots or reduced awareness, especially in tight parking situations or lane changes.

**Can the vehicle be driven?**Yes, but with caution. If the mirror adjustment feature is vital for safe driving in your particular model or situation, consider having the issue addressed promptly.

Symptoms of trouble code B1740

When this code is active, drivers might notice specific symptoms that can help identify the problem:

• Mirror adjustment controls do not respond
• Mirror movement is erratic or stuck in a position
• Warning lights related to mirror or body control systems
• Unusual noises or electrical behaviour when using mirror controls
• In some cases, the mirror may vibrate or flicker during adjustment attempts

Most likely causes of trouble code B1740

This fault is most often caused by issues related to wiring, switches, or internal component failure. Below are the most probable causes, listed from most to least common:

1. Short circuit or damaged wiring in the mirror adjustment circuit — Usually caused by wear, pinched wires, or corrosion in connectors.
2. Faulty driver-side mirror horizontal adjustment switch — The switch button or internal components may be defective or stuck.
3. Corrosion or dirt within the switch or connectors — Moisture ingress can cause intermittent or permanent shorts.
4. Malfunctioning or damaged body control module (BCM) — If the ECU misreads signals or has internal faults.
5. Internal wiring damage due to previous repairs or modifications

How to diagnose trouble code B1740

Diagnosing this fault requires a systematic approach to identify the root cause. Here are generic steps to assist the process:

1. Visually inspect the wiring harness and connectors around the driver’s side mirror area. Look for signs of wear, corrosion, or damage.
2. Check the condition of the mirror adjustment switch, ensuring it moves freely and shows no visible signs of internal failure.
3. Use a multimeter or diagnostic scanner to read live data or sensor status, focusing on the mirror control signals.
4. Test continuity of the wiring circuit from the switch to the vehicle’s body control module (BCM).
5. Clear the fault code and operate the mirror control to see if the code re-appears, indicating an active fault.
6. Inspect the BCM for related codes or faults that could influence mirror operation.

Possible repairs for trouble code B1740

Once the root cause is identified, repairs might include the following actions. Most repairs should be carried out by trained professionals to ensure safety and proper function.

• Repair or replace wiring harnesses or connectors — Basic repair if damage is minor, or full replacement if wiring is severely compromised.
• Replace the mirror adjustment switch — Required if the switch is faulty or physically damaged.
• Clean contacts and connectors — Remove corrosion or dirt that may cause shorts or poor contact.
• Replace or upgrade the body control module (BCM) — If internal faulting or malfunction is confirmed.
• Check and repair internal wiring or components within the mirror assembly — For internal faults or damages.

Vehicles commonly associated with trouble code B1740 in Europe

In Europe, this code is most frequently observed in vehicles where mirror control systems are integrated with the body control unit. Many makes and models may show this fault, especially in models with electronically controlled mirrors.

Groupings include:

• Volkswagen Group: Volkswagen, Audi, Seat, Skoda — related to the electrical mirror adjustment system
• Ford: Many models with body control and mirror modules
• BMW: Particularly models with complex mirror control circuits

Frequent mistakes with trouble code B1740

Diagnosticians and vehicle owners should be cautious of common pitfalls that could delay proper repair, such as:

• Replacing parts without confirming the actual cause — For example, swapping out the switch without testing wiring or connector integrity.
• Ignoring visual checks prior to electrical testing — Missing damage, corrosion, or wiring issues that are apparent on inspection.
• Clearing codes prematurely — Doing so without repairing the root cause, leading to recurring faults.
• Assuming the fault is in the switch alone — Ignoring possible wiring or BCM defects.

Quick FAQ — trouble code B1740

Can this code disappear on its own? As a general rule, no. Faults related to wiring or switch failure usually require intervention. Sometimes, intermittent shorts may temporarily clear, but the underlying cause remains.

Can I keep driving? Yes, but with caution. If the mirror adjustment feature is critical for your safety or compliance, it’s best to have it inspected promptly.

Why does the code return after clearing? If the root cause, such as damaged wiring or a faulty switch, is not repaired, the code will inevitably reappear when the circuit shorts again or the fault recurs.