What a back view mirror does and why you need one
Your back view mirror — also called the rearview mirror — is the mirror mounted on your windshield inside the car, pointing backward. It shows you what is behind your vehicle without turning your head. This matters because it lets you see traffic, pedestrians, and obstacles before you brake, change lanes, or back up, which is why every car sold in the United States is required to have one.
The mirror itself is a flat or slightly curved piece of glass coated on the back with reflective material. Light bounces off that coating and into your eyes, creating the image you see. The frame holds the mirror at an angle so the reflection points toward the driver's seat, and the mounting bracket attaches it to the windshield or the headliner (the fabric ceiling inside the car).
A back view mirror is different from your side mirrors, which show the areas to your left and right. Together, all three mirrors create a view of most of the space around your car — though there are still blind spots where a mirror cannot see, which is why turning your head before changing lanes is still important.
Key Takeaways
- The back view mirror reflects light from behind your car so you can see traffic and obstacles without turning around.
- Most back view mirrors have a manual or automatic dimming feature that reduces glare from headlights behind you at night.
- If your mirror is loose, cracked, or fogged, it needs repair or replacement because it affects your ability to see clearly.
- Adjusting your mirror correctly — so you see mostly road and a thin slice of your car's rear — takes a few seconds and improves your view.
How to adjust your back view mirror for the best view
Sit in the driver's seat in your normal driving position. Grab the mirror frame or the adjustment knob (usually on the back or bottom of the mirror) and tilt it so you see the road and traffic behind you. The goal is to see mostly the road stretching behind your car, with just a thin edge of your car's rear visible on the sides of the mirror.
If you see too much of your own car and not enough road, the mirror is tilted too far down or toward you. If you see mostly road but cannot see your car's rear at all, it is tilted too far up or away. The right position takes practice, but once you find it, you should be able to see a car approaching from behind in any lane, and you should see pedestrians or cyclists on the road behind you.
Some mirrors have a small lever or button on the back that switches between day and night modes. In night mode, the mirror tilts slightly to reduce the glare from headlights behind you, which can be blinding. Check your mirror's manual or look for a small lever if bright headlights are a problem.
Automatic dimming mirrors and how they work
Many newer cars have mirrors that dim automatically when headlights behind you are bright. These mirrors contain a light sensor and a layer of electrochromic material — a substance that darkens when electricity passes through it. When the sensor detects bright light from behind, it sends a small electrical current to the mirror coating, which darkens to reduce glare.
Automatic dimming mirrors usually have a switch or button labeled "Auto" or a symbol showing a mirror with a sun. Turning this feature on or off is your choice; some drivers prefer it, others find it distracting. The mirror returns to normal brightness within a few seconds after the bright light passes.
If your automatic dimming mirror stops working, the sensor or the electrical connection may have failed. This does not make the mirror unsafe — it just stops dimming. You can still use the mirror normally, and you can switch to manual night mode if your mirror has that option.
Common problems with back view mirrors and when to fix them
A loose mirror vibrates or moves when you hit a bump, making it hard to see clearly. The mounting bracket may have come loose from the windshield or headliner. Tightening the bracket usually fixes this, but if the adhesive holding the bracket to the windshield has failed, the mirror may need to be remounted or replaced.
A cracked or chipped mirror distorts the image and creates blind spots. Even a small crack can split the reflection into pieces, making it unsafe to rely on. A cracked mirror should be replaced, not repaired, because the damage usually spreads and the mirror will eventually fail.
A fogged or cloudy mirror happens when moisture gets between the glass and the reflective coating on the back. This is usually permanent and means the mirror seal has failed. Fogging makes the reflection dim and blurry, so the mirror should be replaced.
A mirror that will not stay in position after you adjust it may have a worn pivot joint or a broken adjustment mechanism. If you adjust it and it slowly drifts out of position, the internal mechanism needs repair or replacement.
Replacing a back view mirror
If your mirror is damaged or broken, you have two main options: replace just the mirror glass, or replace the entire mirror assembly (glass plus frame and bracket).
Replacing the mirror glass alone is cheaper and faster. You can buy a replacement mirror glass that matches your car's size and shape, and it usually attaches with adhesive or clips to the existing frame. This works if the frame and bracket are still in good condition. Many auto parts stores sell universal mirror glass kits, and some are made for specific car models.
Replacing the entire mirror assembly is necessary if the frame is cracked, the bracket is broken, or the automatic dimming feature has failed. You will need to remove the old mirror from the windshield or headliner and install the new one. Some assemblies bolt on, others are glued. If your car has automatic dimming, you may also need to connect an electrical plug. A mechanic or glass shop can do this, or you can do it yourself if you are comfortable with basic car work.
The difference between your back view mirror and your side mirrors
Your back view mirror shows you what is directly behind your car. Your two side mirrors (left and right) show you what is to the sides and slightly behind. Together, they cover most angles around your car, but not all — there are still blind spots on either side where a car can hide between your side mirror and your back view mirror.
This is why checking your back view mirror before braking or backing up is important, and why turning your head to check your blind spot before changing lanes is still necessary. No mirror setup can see everywhere at once. The mirrors give you most of the picture, but your head turn fills in the gaps.
Side mirrors can be adjusted from inside the car using a control dial or buttons, and they can also be folded in or out. Your back view mirror usually cannot be folded, and it is adjusted by hand or with a small lever. If your car has automatic dimming on the back view mirror, the side mirrors usually do not have this feature.
Frequently Asked Questions
Why does my back view mirror show a distorted or wavy image?
The mirror glass may be slightly warped, or the reflective coating on the back may be damaged. If the distortion is minor, it is usually just an optical quirk of that particular mirror. If it is severe or gets worse, the mirror should be replaced because a distorted image can make it hard to judge distance and speed of vehicles behind you.
Can I replace my back view mirror myself?
Yes, if you are replacing just the mirror glass. You can buy a replacement glass kit and attach it to your existing frame using the adhesive or clips provided. If you need to replace the entire assembly or reconnect electrical wiring for automatic dimming, it is more involved, and a mechanic or glass shop may be faster and safer.
What should I do if my mirror keeps fogging up?
Fogging between the glass and the reflective coating means the seal has failed, and the mirror cannot be dried out or fixed. The mirror will need to be replaced. You can buy a replacement mirror glass or a full assembly depending on whether the frame is still in good condition.
Is it legal to drive without a back view mirror?
No. Federal law requires every car to have a back view mirror. If yours is broken or missing, you should have it repaired or replaced before driving. If it is temporarily unavailable, you should not drive the car until it is fixed.
Why does my automatic dimming mirror sometimes not dim when I need it to?
The sensor may be dirty or blocked, or the automatic dimming feature may be turned off. Check that the "Auto" button or switch is on. If it is on and the mirror still does not dim, try cleaning the sensor (usually a small spot on the mirror) with a soft cloth. If cleaning does not help, the sensor or electrical connection may have failed.