How It Works: The magic behind some of your vehicle's features

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We do a lot with our vehicles – lock them with the fob, put up the windows, turn on the wipers – without thinking about it.

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But there’s a lot going on “behind the scenes” for these functions to work so seamlessly, and how they do it might surprise you. Here are the secrets behind some of your vehicle’s features.

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An open-and-shut case

Most vehicles open or lock their doors when you press the key fob. Some also do this when you touch the door handle, or even when you’re close to the vehicle, as long as the fob is in your pocket.

The magic is radio signals, which the fob uses to communicate with a module in the vehicle. The fob sends a code, the module receives it, and if they match, the car unlocks its doors. For theft protection, the system uses “rolling” or “hopping” codes that change each time, to prevent anyone capturing the code with an electronic device, and then opening your vehicle.

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An open-but-not-always-shut case

Several vehicles have auto-down windows, where you tap the switch to open the window all the way. But not every one-touch down window is also one-touch up.

It’s because auto-up windows must have an auto-reverse sensor. If the sensor detects something in the way, such as fingers, the window motor immediately reverses direction to avoid injury. If the automaker didn’t opt to spend for that sensor, your window is auto-one-way only.

The difference is night-and-day

No one likes being blinded by headlights from behind, and so your rearview mirror is equipped to gear down the glare. Manual day-night mirrors have a lever on the bottom that you flip to switch them, while auto-dimming mirrors do it by themselves. Some vehicles have auto-dimming exterior mirrors also.

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The manual version actually has a wedge-shaped mirror inside it, with a piece of plain glass in front. In the “day” position, you’re looking at objects reflected in that internal mirror. When you flip it to “night,” the mirror moves so headlights are reflected up and out of your eyes.

Auto-dimming mirrors use two pieces of glass, coated with electrically-conductive material. Between them is a layer of electrochromic gel, which darkens when exposed to electric current. When it’s dark outside, sensors monitor light hitting the mirror. When headlights are detected, the control unit sends electricity to the glass, and the gel darkens. Once the lights are gone, the power switches off, and the gel goes clear again.

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Making sense of rain

Rain-sensing wipers, which are becoming available on a wide variety of vehicles, can be left on all the time. They not only know it’s raining, but how much, and adjust their speed as required.

Most use a sensor mounted behind the windshield, close to the rearview mirror. Whenever the wiper switch is turned on, the sensor aims infrared light at the glass, at a 45-degree angle, and then determines how it reflects back. Water droplets reflect the light differently, and this tells the sensor it’s raining, and how much, so it can activate the wipers.

Seeing the light

Automatic headlamps come on by themselves, using a photoelectric sensor on top of the dash, or by the rearview mirror. When ambient light drops, either with nightfall, or when you’ve gone into a garage or tunnel, the sensor activates the headlamps. They don’t always come on in low-visibility daytime situations such as rain or fog, so be sure to switch the lights on manually in these conditions.

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An increasing number of vehicles add automatic high-beam headlamps. These use a forward-facing camera or sensor to assess how much light there is overall — you want high-beams on a dark rural road, not in a brightly-lit city. If the area is sufficiently dark, the high-beams come on. If the sensors detect oncoming headlights, they shut the high-beams off, and then switch them back on when it’s completely dark again. It sounds like brand-new technology, but GM introduced a similar system, called Autronic Eye, back in 1952.

Pressure looker

Tire pressure monitoring systems (TPMS) aren’t mandatory on new vehicles in Canada as they are in the U.S., but most vehicles here have them. They warn when a tire falls below the recommended air pressure.

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There are two types. Direct TPMS uses sensors inside the tire to measure the pressure. Most are part of the tire valve, but a few are strapped around the inside of the rim. Indirect TPMS uses the speed sensors from the anti-lock brake system (ABS) to determine if one wheel is spinning at a different speed, which can indicate a low tire. Direct TPMS is more accurate, but doesn’t work if the wheels don’t contain sensors – such as when you switch to winter rims and tires – and their batteries eventually run down. Indirect TPMS works on all tires and doesn’t need batteries.

There’s no free air

This isn’t part of your vehicle, but we’ll throw it in. It used to be free to pump up your tires, but gas stations now charge as much as two bucks for air — and it’s not just because they can. It was free when gas stations contained repair shops, and the air pump ran off the shop compressor that powered the tools. Now the mechanics are gone, replaced with a convenience store. The compressor is there solely to run the air pump, and your toonie goes toward the cost of its installation and maintenance.