How To Turn On Heated Mirrors

Heated mirrors, a seemingly simple feature, are a testament to automotive engineering's constant pursuit of safety and convenience. This article provides an in-depth exploration of how they work, their evolution, and their place in the modern automotive landscape. We will cover the technical specifications, engineering choices, real-world performance, and reliability aspects crucial for automotive professionals.

Activating Heated Mirrors: A Practical Guide

The method of activating heated mirrors varies across vehicle manufacturers and models. However, the most common methods are:

Dedicated Button: Many vehicles, particularly older models, feature a dedicated button, often symbolized by a mirror icon with wavy lines representing heat. Pressing this button typically activates the heating element in both side mirrors.
Rear Defroster Synchronization: A widespread approach is to link the heated mirrors to the rear window defroster. Activating the rear defroster simultaneously engages the heated mirrors. This is often the most economical and simple integration choice.
Automatic Activation: Some high-end vehicles incorporate sensors that detect ambient temperature and moisture. If the temperature drops below a certain threshold (e.g., 4°C or 40°F) and moisture is detected, the heated mirrors automatically activate. This system may also be linked to rain sensors on the windshield.
Infotainment System Control: Modern vehicles with sophisticated infotainment systems sometimes integrate heated mirror control within the touchscreen interface. This allows for granular control over the feature but can be less intuitive than a physical button.

Before assuming a malfunction, consult the vehicle's owner's manual to understand the specific activation procedure. Familiarizing yourself with the location of the control and the indicator light (if present) is essential for efficient troubleshooting.

Technical Specifications and Engineering Choices

The core of a heated mirror is the heating element. This is typically a resistive element embedded within the mirror glass assembly. Here's a breakdown:

Resistive Element: The element is usually a thin-film resistor, often made of a metallic alloy like nickel-chromium (NiCr). This material offers a good balance of resistance, thermal stability, and corrosion resistance. The element is designed to distribute heat evenly across the mirror surface.
Power Consumption: Heated mirrors typically draw between 1 and 3 amps per mirror, depending on the size of the mirror and the desired heating rate. A typical vehicle with two heated mirrors might draw 2-6 amps total, translating to roughly 25-75 watts.
Temperature Control: Most heated mirror systems are designed to reach a surface temperature of around 40-50°C (104-122°F). A thermostat or temperature sensor may be incorporated to prevent overheating and potential damage to the mirror glass or housing. In simpler designs, the heating is time-limited by the Body Control Module (BCM) or the defrost timer.
Wiring and Connections: Robust wiring and connectors are crucial for reliable operation. The wiring harness must be designed to withstand exposure to moisture, vibration, and temperature fluctuations. High-quality connectors with proper seals are essential to prevent corrosion and electrical shorts.

The design of the mirror glass itself also plays a role. The glass must be thin enough to allow heat to transfer efficiently to the surface but strong enough to withstand impacts and vibrations. Some manufacturers use coated glass to improve thermal conductivity and heat distribution. Consideration must also be given to the mirror's reflective coating, ensuring it is not negatively impacted by the heat.

Engineering Trade-offs

Engineers face several trade-offs when designing heated mirrors:

Heating Rate vs. Power Consumption: A faster heating rate requires more power, potentially impacting fuel efficiency and putting a greater load on the vehicle's electrical system. A slower heating rate might be insufficient for quickly clearing ice or fog.
Heat Distribution vs. Cost: Even heat distribution is essential for optimal performance. However, complex heating element designs and advanced materials can increase manufacturing costs.
Reliability vs. Complexity: Simpler designs are generally more reliable. However, more complex systems with temperature sensors and automatic activation can offer greater convenience and efficiency.

Real-World Performance and Comparisons

Heated mirrors are highly effective in clearing frost, ice, and fog from the mirror surface, improving visibility and safety, especially in inclement weather. They outperform non-heated mirrors significantly in these conditions. The effectiveness, however, depends on several factors:

Ambient Temperature: The colder the ambient temperature, the longer it takes for the heated mirrors to clear the surface. In extreme cold, the heating element may struggle to keep the mirror completely clear.
Moisture Level: Heavy snow or freezing rain can overwhelm the heating element, especially if the system is not operating at full capacity.
Vehicle Speed: At higher speeds, airflow can help clear moisture from the mirror surface, reducing the load on the heating element.
System Age: Over time, the heating element can degrade, reducing its effectiveness. Wiring and connectors can also corrode, leading to reduced performance.

Alternatives and Their Pros and Cons

While heated mirrors are a common solution, other technologies exist:

Mirror Defrosting Sprays: These sprays chemically melt frost and ice.
Pros: Relatively inexpensive, can be used on any vehicle. Cons: Requires manual application, effectiveness can be limited, chemicals may damage mirror surface.
Hydrophobic Coatings: These coatings repel water, reducing the build-up of moisture on the mirror surface.
Pros: Passive solution, relatively inexpensive, improves visibility in rain. Cons: Not effective against ice or frost, requires periodic reapplication.
Ultrasonic Vibration: Using ultrasonic vibrations to dislodge ice and water.
Pros: No heating element required, energy efficient. Cons: More complex and expensive to implement, effectiveness can be limited by ice thickness.

Heated mirrors provide the best balance of effectiveness, convenience, and cost compared to most alternatives, making them the preferred choice for many vehicle manufacturers.

Reliability Aspects and Maintenance Tips

Heated mirrors are generally reliable, but failures can occur. Common issues include:

Heating Element Failure: The resistive element can burn out over time, especially if the system is frequently used or exposed to high temperatures.
Wiring and Connector Corrosion: Moisture and road salt can corrode wiring and connectors, leading to electrical shorts or open circuits.
Thermostat Failure: If the system uses a thermostat, it can fail, causing the heating element to overheat or not activate at all.
Fuse Failure: A blown fuse can disable the heated mirrors. Check the fuse box and replace any blown fuses.

Regular maintenance can help extend the life of heated mirrors:

Inspect Wiring and Connectors: Periodically inspect the wiring and connectors for signs of corrosion or damage. Clean corroded connections with a wire brush and apply dielectric grease to protect them from moisture.
Test the System: Regularly test the heated mirrors to ensure they are functioning correctly. Check the mirror surface temperature to verify that the heating element is working effectively.
Replace Damaged Components: If any components are damaged, replace them promptly to prevent further damage to the system.

When replacing a heated mirror, use only high-quality replacement parts that meet the vehicle manufacturer's specifications. Ensure that the replacement mirror is compatible with the vehicle's electrical system.

Future Trends

The future of heated mirrors will likely involve:

Integration with Advanced Driver-Assistance Systems (ADAS): Heated mirrors may be integrated with ADAS features such as blind-spot monitoring and lane departure warning systems. This integration could improve the performance of these systems in inclement weather.
Improved Heating Element Technology: New materials and designs could lead to more efficient and reliable heating elements. Self-regulating heating elements that automatically adjust their output based on ambient conditions could further improve efficiency.
Smart Mirror Technology: Combining heated mirrors with electrochromic dimming, cameras, and other sensors could create "smart" mirrors that provide enhanced visibility and safety features.
More efficient power management: Better integration with the vehicle's overall energy management system to optimize power usage. This could involve using predictive algorithms to anticipate the need for heated mirrors and pre-emptively activate them.

Furthermore, the increasing prevalence of camera-based side-view "mirrors" (CMS - Camera Monitoring Systems) will impact the future of heated mirrors. While offering benefits in terms of aerodynamics and field of view, CMS still require measures to ensure clear visibility in inclement weather. Heated camera lenses and software-based image enhancement could be alternatives to traditional heated mirrors in this context.

Conclusion

Heated mirrors, while a seemingly simple convenience feature, represent a thoughtful application of engineering principles to enhance vehicle safety and usability. As the automotive industry continues to evolve, we can expect further advancements in heated mirror technology, driven by the pursuit of greater efficiency, reliability, and integration with advanced vehicle systems. Understanding the technical aspects, performance characteristics, and maintenance requirements of heated mirrors is crucial for automotive professionals in diagnosing and resolving issues, as well as staying abreast of emerging trends in the industry. The integration of these systems within larger ADAS frameworks, and the potential replacement by CMS, highlights the dynamic nature of automotive technology and the need for continuous learning within the profession.