Car side mirror and rearview mirror: silent guardians of driving safety and their technical soul

A modern vehicle is a complex electromechanical system, where every detail plays a specific role. If the engine is the heart of the car and the electronics are its brain, then the mirrors are undoubtedly the eyes of the car. Driving a vehicle without a complete overview of the surroundings is unthinkable and extremely dangerous. Historically, the car mirror system has evolved from a simple piece of polished metal or glass to a complex technological assembly that includes heating elements, electric motors, memory modules, temperature sensors and even turn signals.

In this in-depth article, we'll take a look at the basics of car mirror management. We won't just talk about how to adjust a mirror, we'll dive deep into the system. We'll explore what's going on behind the exterior mirror adjustment switch , why the mirror heater stops working, how the interior mirror is constructed, and what are the common faults of different car brands. This is a guide for both the car owner who wants to better understand their vehicle and the hobby mechanic who is faced with the need for a repair.

1. Side mirror or exterior mirror: anatomy and structure

A car's side mirror is no longer just a single spare part. It is a module consisting of several replaceable components. Understanding what a mirror consists of can save you money – often it is not necessary to replace the entire mirror, but simply replacing one part is enough.

1.1 Mirror cover and housing

The outer shell of the mirror, or mirror cover, is usually painted in the body color or is a contrasting black (matte or glossy). The function of the cover is to protect the interior of the mirror (motors and wires) from wind, rain, snow and road dirt. Since the mirrors are the widest points of the car, it is the covers that can suffer the most in parking lots and narrow streets. On most cars, the cover can be removed and replaced separately, which makes cosmetic repairs affordable.

1.2 mirror frame and mounting foot

This is the "skeleton" of the mirror. The frame is usually made of aluminum alloy or reinforced plastic and is bolted to the door. Wire bundles run inside the frame. If the mirror wobbles or vibrates while driving, the fault is often in the frame itself, broken or loose mounting bolts, not the glass itself.

1.3 adjustment motors

Behind the mirror glass is a round or square block of electric motors. There are usually two small electric motors there: one moves the glass up and down, the other left and right. These motors work on the principle of a worm gear and are quite reliable, but they are sensitive to moisture and icing. If you wash your car in the winter and water gets in between the motor and freezes, the adjustment can break the plastic gears.

2. Mirror glass: more than just a reflection

The mirror glass is the most important, but also the most vulnerable part of the system. In the automotive industry, glasses with different optics are used to improve visibility and reduce dangerous areas.

2.1 Types of glasses

• Flat glass (planar): This is a regular mirror that shows the image without distortion (ratio 1:1). Its disadvantage is a very narrow field of view, which creates a large blind spot. In modern cars, it is rarely used, or only on the passenger side (in US market cars).
• Convex glass: the surface of the glass is slightly spherical. This significantly expands the field of view, but creates an optical illusion - objects appear further away than they actually are. Hence the famous English warning: "objects in a mirror are closer than they appear".
• Aspherical glass: This is the European standard and the safest solution. The glass is largely curved, but its outer edge (often separated by a vertical dotted line) has a sharply greater radius of curvature. This "broken" angle allows the driver to see directly into the car in the next row, almost completely eliminating the blind spot.

2.2 auto-dimming exterior mirrors

Premium cars often have electrochromic, or self-dimming, exterior mirrors. There is a special gel between the layers of glass that darkens when exposed to electric current. This is convenient for nighttime driving, but it makes the price of the spare part many times higher. A typical malfunction is gel leakage – the glass turns brown or a "bubble" forms.

3. mirror heating and its diagnostics

In our climate, mirror heating is an indispensable helper. It is necessary not only to melt ice in winter, but also to remove raindrops and fog in autumn and spring. A dry mirror ensures a clear image and safety.

How does the system work?

In simpler systems, the mirror heater is connected to the rear window heater and is switched on with the same button. In more complex cars, the heater is controlled by the door control unit or the air conditioning system, which switches the heater on automatically when the outside temperature drops below a certain limit (e.g. +5°C).

Why is the heating not working?

It is worth starting troubleshooting from the simplest to the most complex:

1. fuse and outside mirror heating relay: check the fuse box for the corresponding fuse. Older cars may have a separate relay that has burnt out the contacts.
2. Heating element on glass: this is statistically the most common fault. A resistance wire is glued or evaporated to the back of the mirror glass. Over time, a microcrack or corrosion occurs and the circuit is interrupted. The diagnosis is simple: remove the glass, take a multimeter and measure the resistance between the two terminals. If the resistance is infinite, the heating element is broken and the mirror glass must be replaced.
3. Wires in the door hinge: if the mirror glass is fine and the fuses are intact, the problem may be in the rubber seal between the door and the body. Constant opening and closing of the door breaks the wires inside.

4. Adjustment and folding: switches and electronics

The entire mirror system is controlled by the car's mirror adjustment button or exterior mirror adjustment switch located in the cabin. It is a small but complex electromechanical device.

switch construction and faults

The switch consists of a circuit board and physical contacts. Since the switch is often located on the door trim (armrest), it is exposed to rain (when the door or window is open) and dust. Moisture and dirt cause oxide to form, causing the switch to no longer make contact. A symptom is when the mirror only moves up and down, but not left and right.

electric folding (power folding)

a convenience feature that folds the mirrors against the body when parked. the mechanism consists of a separate electric motor and reducer. a common problem is when the mirror "rides over", i.e. does not stop in the correct position, or moves with great difficulty. the cause is often the hardening of the lubricant inside the mechanism or the breakage of the plastic limiter.

5. Interior mirror or rearview mirror: from simplicity to high technology

The rear-view mirror , or interior mirror, is located on the windshield and gives the driver a view directly behind. There has also been a major development here.

5.1 ordinary prism mirror

This is a classic solution, where there is a small "click" at the bottom of the mirror. The glass is wedge-shaped (prism). In the daytime position, it reflects light from the rear (silvered) surface. In the night position, moving the click changes the angle of the mirror so that the driver sees the reflection from the front (glass) surface, which is much dimmer and does not dazzle.

5.2 automatically dimming (electrochromic) interior mirror

This is a convenience feature that works without the driver's intervention. The mirror housing has two light sensors: one facing forward (measures the ambient light) and the other facing backward (measures the lights of a car coming from behind). If the rear sensor receives a stronger signal than the front one (for example, it is dark and someone is driving behind with full headlights on), the electronics give the command to darken the glass.

Warning: Auto-dimming mirrors contain a corrosive fluid. If the mirror is hit or becomes old, this fluid may leak. If it gets on the dashboard, gear lever or seat covers, it will corrode the plastic and leather, permanently damaging them. If a leak occurs, the mirror must be removed immediately.

6. common car model errors

Each car manufacturer has its own engineering characteristics, which also manifest themselves in specific problems with mirrors.

BMW (3 Series E46/E90, 5 Series E39/E60, X5)

• lin-bus errors: bmw mirrors are often connected to the car's data interface. if one mirror fails (the electronics get wet), it can "take down" the entire door electronics, causing the windows and central locking to not work either.
• Mirror "overturning": E46 and E39 models have a common fault where the electrically folding mirror does not stop in the correct position, but instead turns 180 degrees forward. The fault is in the position sensor or microswitch inside the motor.
• Window heating: BMW often heats the mirrors continuously. This burns out the heating element over time and causes brown spots on the glass.

volkswagen group (vw golf, passat, audi a4/a6, skoda)

• Adjustment knob breakage: On VAG Group cars, the car mirror adjustment knob is a small joystick that is physically quite fragile. It tends to simply break off. Fortunately, it is a cheap spare part.
• Glass bonding: Passats and Golfs have had problems where the glass separates from the heating element and simply falls off.
• Turn signal in mirror: The LED turn signal in the mirror housing tends to let moisture in and stop working. Upon inspection, this is an immediate fault.

mercedes-benz (c-class, e-class)

• Wire insulation: Older models (late 90s, early 2000s) used biodegradable wire insulation. The wires inside the mirror would fray, causing short circuits and strange anomalies.

honda and toyota (civic, avensis, cr-v)

• Slow folding: Japanese cars have a common fault where the "poly fuse" (thermal fuse) in the mirror folding mechanism becomes fatigued. The mirror moves very slowly or stops halfway. Repair requires dismantling the module and replacing the component.

Volvo (V70, S60, S80 - P2 and P3 platform)

• Temperature sensor: Volvo has an outside temperature sensor in the right (passenger) mirror. If it breaks down or the connection oxidizes, the car's instrument panel will show the wrong temperature and – even worse – the engine control unit and air conditioning system may start to function incorrectly (e.g. the air conditioning will not blow cold).

7. Spare parts selection and recommendations

If your mirror needs replacing, there are a wide range of options on the market. You don't always have to rush to the dealership for an original part, but it's worth being careful.

original (oem) vs. aftermarket

For mirror covers and turn signals, B-parts (aftermarket) are usually a very good alternative. But for mirror glass and engines, the quality difference is more noticeable.

Well-known and reliable aftermarket brands are:

• tyc and depo: these are large asian manufacturers whose products are very close to the original in quality. their mirrors fit well and the glass does not distort.
• alkar: european (spanish) manufacturer, specialized in mirrors. good price-quality ratio.
• van wezel and blic: large packagers whose boxes often contain products of decent quality.
• vemo: a good choice for electrical components such as switches and motors.

What to look for when buying glass?

When choosing glass, make sure you order glass with the correct curvature (whether you want aspherical or convex). Also check if the glass has heating terminals. The cheapest glasses are often unheated and have a simple "flat mirror", which makes driving uncomfortable. In the case of category B glasses, the image can sometimes have a slight "waving" at the edges, so it is worth giving preference to more well-known manufacturers.

8. Maintenance and prevention

How to extend the life of mirrors?

• Silicone oil: At the beginning of winter, it's a good idea to put a little silicone oil between the mirror folding mechanism. This will keep water out and prevent icing.
• Do not force fold manually: If your car has electrically folding mirrors, avoid moving them manually. This can damage the gear wheels of the reducer.
• Clean the drains: Some mirrors have small holes under the housing to drain water. Make sure they are not clogged with dirt so that water does not collect inside the housing and drown the electronics.

In conclusion , car mirrors are a critical part of your safety equipment. Keeping them in good condition – clean and intact glass, working heating and smooth adjustment – ​​ensures that you always have full control over the situation in traffic. Timely diagnostics and the use of high-quality spare parts ensure years of worry-free driving.