B1746 — Mirror Passenger Horizontal Switch Circuit Open

**Overview of the code**

OBD-II trouble code B1746 indicates that there is an electrical issue related to the passenger side mirror’s horizontal adjustment switch. In simple terms, the vehicle’s electronic control unit (ECU) detects a problem in the wiring or switch circuit responsible for controlling the mirror’s left-right movement. It’s important to note that the label or description may vary depending on the vehicle manufacturer, but the functional focus remains on the passenger side mirror’s horizontal switching system.

**Fast Facts**

  • System affected: Mirror control switch circuit
  • Severity: Moderate
  • Main symptoms: Mirror adjustment malfunction, warning light illumination in some cases
  • Driveability: Yes

—

**Manufacturer variations for trouble code B1746**

Different vehicle manufacturers may assign unique labels or codes that point to similar underlying issues. Such variations can make diagnosis a bit more complex if you’re unsure about the exact vehicle specifications.

Typical label variations for B1746 include:

  • Honda: B1746 – Passenger Side Mirror Horizontal Switch Circuit Open
  • Ford: B1746 – Passenger Mirror Adjust Switch Circuit Fault
  • Volkswagen: B1746 – Passenger Side Mirror Adjustment Circuit Open
  • BMW: B1746 – Passenger Mirror Control Circuit Malfunction

It’s crucial to consult the specific vehicle’s repair manual or technical documentation to confirm label correspondences.

—

**What does trouble code B1746 mean?**

This diagnostic trouble code (DTC) signals that the ECU has detected an problem in the circuit connected to the passenger side mirror’s horizontal adjustment switch.

The ECU continuously monitors electrical signals, wiring integrity, and switch operation. When faulty signals are observed—such as an open circuit, short circuit, or malfunctioning switch—the code gets stored.

Typically, this code appears in situations where a passenger mirror’s left-right adjustment no longer functions correctly or intermittently, often accompanied by a dashboard warning light. The problem can be caused by wiring issues, switch failures, or even connector problems.

—

**Severity and risks of trouble code B1746**

This code represents a moderate level of severity. It primarily affects the functionality of the passenger side mirror, specifically the horizontal adjustment feature. While it does not directly impact vehicle safety or drivability, it can hinder visibility adjustments and, consequently, driver awareness.

If left unaddressed, it could lead to:

  • Inability to properly adjust the passenger mirror, impairing visibility
  • Potential distraction if the mirror cannot be set correctly for driving conditions
  • Possible electrical issues evolving if the underlying wiring fault worsens

**Can the vehicle be driven?**
Yes, in most cases, the vehicle remains drivable. However, addressing the issue promptly is advisable, especially if mirror adjustment is essential for safe driving.

—

**Symptoms of trouble code B1746**

Common symptoms related to this code are primarily linked to the malfunction of the passenger mirror’s horizontal adjustment. Drivers might notice:

  • Passenger mirror not adjusting via the control switch
  • Intermittent mirror movement or unresponsiveness
  • Warning lights related to electrical or mirror system
  • Visual inspection revealing damaged wiring or loose connectors near the passenger side mirror

Since mirror control issues are generally localized, many drivers observe a straightforward dysfunction rather than multiple symptoms.

—

**Most likely causes of trouble code B1746**

Understanding the typical causes can streamline diagnosis and repair. The causes are ordered from most common to less common:

1. **Open or damaged wiring in the passenger side mirror circuit** — often caused by wear, corrosion, or physical damage.
2. **Faulty passenger side mirror horizontal adjustment switch** — internal switch failure or malfunction.
3. **Loose or corroded connectors or wiring harness connectors** — especially at the mirror or vehicle door junction.
4. **Blown fuse or relay related to mirror control** — less common but possible in some vehicle configurations.
5. **ECU or body control module (BCM) internal fault** — rare, but it can be a source if all wiring and switches test good.

—

**How to diagnose trouble code B1746**

Diagnosis involves a systematic approach to verify wiring, switch operation, and connector integrity without requiring proprietary manufacturer tools initially.

1. **Visual inspection**
Check the wiring connected to the passenger mirror and control switch for obvious damage, corrosion, or loose connections.
2. **Test the switch**
Operate the passenger side mirror’s horizontal adjustment switch and observe whether the switch responds physically and if the wiring harness shows signs of stress.
3. **Use a multimeter or test light**
Perform continuity tests on the wiring circuits associated with the switch and mirror motor wiring.
4. **Check for voltage supply and ground**
Ensure the switch circuit is receiving proper voltage and grounding.
5. **Examine connectors and wiring harnesses**
Disconnect and inspect connectors for signs of corrosion, dirt, or damage.
6. **Use live data (if available)**
Access the vehicle’s CAN data or body control module (BCM) readings to check if the mirror control signals are being sent and received correctly.
7. **Test the mirror motor**
In some cases, directly testing the mirror motor can confirm whether the fault resides within the motor itself or the control circuit.

—

**Possible repairs for trouble code B1746**

Repair strategies depend on the identified cause and can range from simple to more complex procedures:

– **Repair or replace damaged wiring or connectors** — This is a basic repair typically performed by technicians or capable DIYers.
– **Replace the passenger side mirror adjustment switch** — When the switch appears faulty or fails continuity tests; this repair is straightforward but often requires removing door panels.
– **Fix or replace connectors** — Clean or re-seat electrical connectors where corrosion or looseness is detected.
– **Replace blown fuse or relay** — If the circuit is protected by a fuse or relay, replacing it can resolve the issue.
– **Replace the mirror motor** — When testing indicates the motor itself is defective; this repair is more complex and might require removing the mirror assembly.
– **Reprogram or replace the ECU/BCM** — In rare cases when internal module faults are suspected, professional diagnosis and programming are required.

—

**Vehicles commonly associated with trouble code B1746 in Europe**

This specific code is found across various brands, especially those with electronically adjustable passenger mirrors. Typical affected vehicle groups include:

– **Volkswagen Group**
– VW Golf, Passat, Tiguan, Polo, Audi A3
– **BMW**
– F30, F20, F10 series with electric mirrors
– **Ford**
– Focus, Fiesta, Mondeo
– **Honda**
– Civic, CR-V, Accord with power mirrors

While this list is not exhaustive, it reflects common European models where electrical mirror adjustment systems are standard.

—

**Frequent mistakes & best practices**

Misdiagnosis or incorrect repairs can prolong vehicle downtime or worsen the problem. Recognize typical pitfalls:

– **Assuming the switch is faulty without checking wiring continuity** — always perform electrical testing before replacement.
– **Overlooking connector corrosion or damage** — connectors should be thoroughly inspected during diagnosis.
– **Replacing parts without verifying the actual cause** — such as replacing the switch when wiring is the real culprit.
– **Ignoring the possibility of blown fuses or relays** — check these electrical protections early.
– **Failing to clear DTCs after repairs** — always clear codes and verify that the problem is resolved.

—

**FAQ — trouble code B1746**

Here are some common questions from technicians and vehicle owners:

**Can this code disappear on its own?**
Generally, no. Once stored, this code persists until the fault is fixed and the ECU is reset or the code is cleared with a diagnostic tool.

**Can I keep driving?**
Yes, if the mirror adjustment function isn’t critical for safe driving. However, it’s advisable to repair it promptly to ensure full vehicle functionality and safety.

**Why does the code return after clearing it?**
This indicates the underlying electrical fault or damaged component has not been fixed. The issue is persistent or recurring, so diagnosis and repair are necessary.

Retour en haut