B1740 — Mirror Driver Horizontal Switch Circuit Short To Ground #

Note: The description for code B1740 may vary depending on the vehicle manufacturer. Always refer to your vehicle’s specific service information.

• Mirror Driver Horizontal Switch Circuit Short To Ground (Generic/OEM)
• Driver Side Mirror Horizontal Adjustment Switch Circuit Low (Ford)
• Left Door Mirror Horizontal Motor Switch Shorted (Toyota)
• Outside Mirror Horizontal Position Switch Malfunction (Nissan)

Summary of DTC B1740 #

The B1740 diagnostic trouble code (DTC) indicates a problem within the driver’s side mirror horizontal adjustment switch circuit. Specifically, this code means the circuit is experiencing a short to ground, which disrupts the normal operation of the mirror’s horizontal movement (left-right adjustment). The vehicle’s Body Control Module (BCM) or related control unit detects this abnormal voltage condition when the driver attempts to use the adjustment switch. As a result, the affected mirror may not respond correctly or at all to input commands. Although this is not a safety-critical code, it can be inconvenient and may mask other electrical issues if ignored. Early diagnosis helps prevent further complications in the mirror or related door wiring.

Common Symptoms for DTC B1740 #

A short to ground in the mirror’s switch circuit usually causes noticeable and consistent symptoms. The most obvious is the inability to adjust the driver’s side mirror horizontally, but there can be other clues as well. Here’s what you might notice:

• Driver’s side mirror does not move left or right when using the adjustment switch
• Other mirror adjustment directions (up/down) may still work normally
• Clicking, buzzing, or faint electrical noises from the driver’s door when using the switch
• Mirror adjustment switch feels “dead” or unresponsive
• Intermittent operation if the short is not constant
• Potential illumination of a door module warning light (on some vehicles)

Most Likely Causes of B1740 #

Electrical shorts in mirror adjustment circuits can stem from a variety of issues, but some causes are far more common than others. Here’s a breakdown, in order of likelihood:

1. Damaged or pinched wiring in the door harness, especially where the harness flexes between the door and body (“A-pillar” area)
2. Faulty mirror adjustment switch (internal short to ground)
3. Corroded or water-intruded connectors at the switch or mirror motor
4. Mirror horizontal motor itself shorted internally
5. Incorrect or poor-quality aftermarket parts installed in the circuit
6. BCM or door control module defect (rare)

Step-by-Step Diagnostic for Code B1740 #

Diagnosing an electrical short requires methodical troubleshooting. With B1740, the focus is on the circuit for the driver’s mirror horizontal adjustment. Use a digital multimeter (DMM) and, if available, an OEM wiring diagram to trace the fault. Here’s a proven step-by-step approach:

• 1. Verify the code: Clear the code, operate the mirror switch, and see if B1740 returns.
• 2. Inspect the mirror adjustment switch: Look for physical damage, fluid spills, or unusual wear.
• 3. Check door wiring harness: Gently move the harness between the door and body while operating the switch; watch for intermittent operation or code reset.
• 4. Test for short to ground: With the ignition off, disconnect the mirror switch connector. Measure resistance from the switch’s horizontal circuit wire to ground. Low resistance confirms a short.
• 5. Unplug the mirror motor: If the short remains with the motor disconnected, the issue is upstream (wiring or switch).
• 6. Inspect connectors: Look for corrosion, bent pins, or water intrusion at all connectors in the circuit, especially at the mirror and switch.
• 7. Isolate circuit sections: If needed, disconnect at intermediate connectors to isolate a section of the harness.
• 8. Check the control module (if all else passes): If the wiring and components test good, the BCM or door control module may be malfunctioning.

Possible Repairs for Code B1740 #

Fixing a B1740 code depends entirely on what the diagnosis reveals. Most repairs are straightforward, but precision is key to avoid repeat issues. Here are the most common solutions:

• Repair or replace damaged wiring (especially in the door hinge area where wires flex and break)
• Replace the mirror adjustment switch if an internal short is found
• Clean and secure any corroded connectors (use electrical contact cleaner and dielectric grease if needed)
• Replace the mirror motor assembly if it’s internally shorted
• Install OEM-approved parts to prevent future electrical compatibility issues
• Replace the door control module or BCM only if all wiring and hardware have been ruled out

Is It Safe to Drive With B1740? #

Yes, you can continue driving with code B1740 present, but with limitations. This code does not affect your vehicle’s safety systems or its ability to operate. However, losing the ability to adjust your driver’s mirror horizontally can create a visibility issue, especially if multiple drivers use the vehicle or if the mirror is stuck in a non-optimal position. It’s best to address the fault promptly to maintain full control of your mirror’s position and to rule out any broader electrical issues in the door.

Vehicles Most Commonly Affected by B1740 #

While B1740 is a generic OBD-II/Body code used by many manufacturers, it is most frequently encountered on vehicles equipped with power mirrors and advanced body control modules. The following makes and models have reported this code more often:

• Ford F-Series, Escape, Fusion (various years)
• Toyota Camry, Corolla, RAV4
• Nissan Altima, Sentra, Rogue
• Honda Accord, Civic, CR-V
• GM trucks and SUVs (Chevrolet Silverado, GMC Sierra)
• Hyundai and Kia sedans

Remember, this code can appear in almost any modern vehicle with power-adjustable mirrors, especially as wiring ages or is subjected to frequent movement.

Common Mistakes & Best Practices for B1740 #

Some pitfalls often catch out even experienced techs. Accurate diagnosis and repair will save time and avoid repeat visits. Here’s what to watch for:

• Replacing the mirror switch or motor without checking wiring first (the underlying issue is often in the harness)
• Overlooking corroded or loose connectors hidden inside the door or under weather seals
• Using non-OEM switches or motors that may not meet manufacturer specifications
• Ignoring intermittent faults because they self-clear temporarily (wiggle tests can help reveal these)
• Not consulting an up-to-date wiring diagram specific to your VIN and trim level

Quick FAQ for Code B1740 #

A couple of rapid-fire answers to the most common questions about B1740:

• Q: Can a blown fuse cause B1740?
  A: No, B1740 specifically indicates a short to ground, not an open circuit. However, a blown fuse may be a symptom of the same short.
• Q: Will replacing the mirror glass fix this code?
  A: No, unless the mirror glass contains integrated electronics (like memory or heating features) that are part of the horizontal adjustment circuit. The fault is typically in the switch, wiring, or mirror motor assembly.
• Q: Do I need to reprogram anything after repair?
  A: Usually not for this code. After repair, clear the code and verify proper function. Some vehicles may require a basic reset or mirror calibration, as per OEM procedure.