B1738 — Mirror Driver Horizontal Switch Circuit Open #

Note: The wording of this code may change depending on the vehicle manufacturer (OEM).

• B1738: “Mirror Driver Horizontal Switch Circuit Open” (Ford, Chrysler, Honda, Nissan)
• B1738-11: “Mirror Driver Horizontal Switch Circuit Short to Ground” (Toyota)
• B1738-00: “Mirror Driver Horizontal Switch Circuit Open” (General Motors, Opel/Vauxhall)

Summary of code B1738 #

The B1738 diagnostic trouble code (DTC) indicates an open circuit in the driver side mirror horizontal switch wiring. This means the system has detected a break or disconnection in the electrical path controlling the left mirror’s left/right movement. The switch is typically mounted on the driver’s door panel and allows you to adjust the side mirror horizontally. When the circuit is open, the mirror cannot respond to adjustment commands, which may affect driver comfort and visibility. While this code does not usually indicate a critical safety issue, it can be a sign of wiring problems or component failure that may impact other door functions.

Common symptoms for code B1738 #

When the B1738 code is present, the most noticeable symptom is the inability to adjust the driver’s side mirror horizontally. This can be inconvenient, especially if multiple drivers use the vehicle or if visibility needs to be fine-tuned. You may also notice that the mirror switch feels loose or unresponsive. In some cases, other mirror functions (vertical movement, heating) might still work normally, adding to the confusion.

• Driver’s side mirror does not move left or right
• No response when using the mirror adjustment switch horizontally
• Mirror switch may feel loose or have “dead spots”
• No warning lights in most cases; sometimes a “mirror malfunction” message on the dash
• Other mirror functions (vertical, heating) may still work

Probable causes by frequency for code B1738 #

This code is generally triggered by a break in the electrical connection between the switch and the mirror motor. The most common root causes relate to wear and tear, exposure to moisture, or physical damage to the door wiring harness. Some of these issues can be intermittent, depending on door movement or vibration.

1. Faulty mirror adjustment switch (internal failure or worn contacts)
2. Broken or damaged wiring in the door harness (often in the flex area between door and body)
3. Corroded or loose electrical connectors at the switch or mirror motor
4. Failed mirror motor (horizontal movement circuit open)
5. Blown fuse or relay in rare cases (if shared with other mirror functions)

Step-by-step diagnostic for code B1738 #

A thorough step-by-step diagnosis is crucial to pinpoint the exact failure. Rushing may lead to replacing the wrong part or overlooking a simple wiring issue. Here’s how a professional technician would approach this code:

• Step 1: Confirm the code using an OBD-II/EOBD scan tool; clear the code and see if it returns.
• Step 2: Inspect the mirror switch for physical damage, looseness, or contamination.
• Step 3: Check the mirror adjustment operation—does vertical movement work? Are other mirrors affected?
• Step 4: Remove the door panel and inspect wiring for visible damage, pinched wires, or corrosion, especially in the door hinge area.
• Step 5: Test the continuity of the horizontal circuit wiring using a multimeter from the switch to the mirror motor.
• Step 6: Check the connectors at both the switch and mirror motor for corrosion or loose pins; clean and reseat as needed.
• Step 7: If wiring and connectors are good, test the switch for proper function with an ohmmeter; replace if faulty.
• Step 8: As a last resort, test or replace the mirror motor itself if all wiring and the switch check out.

Possible repairs for code B1738 #

Once the root cause is identified, repairs can range from simple cleaning to component replacement. Always address the underlying issue to prevent recurrence.

• Replace the mirror adjustment switch if internal contacts are worn or broken.
• Repair or replace damaged wiring in the door harness, especially at high-flex points.
• Clean or repair corroded connectors at the switch or mirror motor.
• Replace the mirror motor assembly if the horizontal circuit is open internally.
• Replace blown fuses or relays only if they have failed and after confirming the cause (rare for this code).

Is it safe to drive with code B1738? #

Yes, you can safely drive with code B1738 present. This code does not affect engine, braking, or critical safety systems. However, you may find it difficult to adjust your driver’s side mirror for optimal visibility, which could be a minor safety concern, especially if multiple drivers use the car or if you need to adjust for towing or parking. It is best to repair it at your earliest convenience, but it will not leave you stranded.

Vehicles most commonly affected by code B1738 #

While any vehicle with power mirrors can encounter this code, it is most frequently seen on models where the mirror switch and wiring are exposed to frequent use or moisture. The following vehicles are often reported with B1738 in forums and repair databases:

• Ford F-Series (F-150, F-250, etc.)
• Honda Accord and Civic
• Chrysler 300, Dodge Charger
• Nissan Altima, Sentra
• Chevrolet Silverado, GMC Sierra
• Toyota Camry, Corolla (variant B1738-11)

Common mistakes & best practices for code B1738 #

Misdiagnosis is common with electrical mirror faults. Technicians sometimes replace the mirror motor or switch without checking the wiring, leading to unnecessary costs. Use a methodical approach and avoid these pitfalls:

• Assuming the switch is always the problem—wiring damage is just as common.
• Not inspecting the door harness flex point, where wires often break due to repeated door opening/closing.
• Overlooking corroded connectors—moisture intrusion is a frequent culprit.
• Replacing the mirror motor prematurely without confirming a circuit open inside it.
• Best practice: Always test for continuity and check for 12V power and ground at the mirror connector before replacing parts.

Express FAQ for code B1738 #

Here are quick answers to some common questions about this code:

• Q: Can I fix code B1738 myself?
  A: If you’re comfortable removing the door panel and using a multimeter, you can check for obvious wiring or switch problems. However, professional diagnosis is recommended for hidden wiring faults.
• Q: Will the mirror adjustment work again if I clear the code?
  A: Clearing the code alone will not restore mirror function. The underlying electrical fault must be repaired for the feature to work reliably again.