10 Problems Cars Can Diagnose By Themselves

How does your car communicate with you? C. Lyttle/Corbis

Finding 10 problems a car can diagnose on its own is actually a lot harder to pin down than you might think. Now that we're firmly in the twenty-first century, a better question might be, "What problems can't a car diagnose for itself?" Other reasonable questions: "If my car knows so dang much, why isn't it as cool as K.I.T.T.?" and "Are cars actually our robot overlords?"

Cars today are surrounded by sensors -- they're in the engine, the tires, the reservoirs, the windshield, the electrical system, the seat, your brain ... wait. No, not your brain. Probably. All these sensors and the systems that keep track of them are known as on-board diagnostics, or OBD (not to be confused with deceased rapper ODB).

The point is that vehicles of all kinds can keep track of their own health. The problem often comes when they try to communicate their information with the driver. Like a cranky baby who cries no matter what is wrong, from an ingrown fingernail to Hantavirus, cars will light up that "service engine" light in the dashboard for nearly every problem from a loose gas cap to an engine that's about to explode.

And that's where the diagnostic trouble codes come in. The car's computer spits out a code that can only be deciphered by a reader, which is usually in the hands of your mechanic. He'll probably tell you your gas cap is loose, and you'll want to kick in your own windshield to teach the car a lesson about what's important in this life. Robot overlords indeed.

But there are specific things a car can diagnose and share with you in plain English. Here are 10 of the most common and most interesting, in no particular order.

Change Is Good
Some newer cars can monitor your driving habits and make oil change suggestions accordingly. Najlah Feanny/Corbis

Back in the bad old days, conventional wisdom said everyone had to change their engine oil every 3,000 miles (4,828 kilometers) (or until their dad bawled them out for leaving that crud in the engine for more than three months.) Then engine technologies and oil formulations improved, and that guideline was raised to 5,000 miles (8,047 kilometers), then 10,000 miles (16,093 kilometers).

Miles are so old-school, yo.

All the cool kids now have sensors that can tell how filthy your oil is. Cars also monitor your driving habits and make oil change suggestions accordingly. Drive low and slow? You can squeeze out a few more miles. Treat every red light like the drag race in "Better Off Dead?" You're going to need to change that oil often. And your overlord ... er, car will tell you about it. And if that car is a BMW with its fancy teleservice system, it'll rat you out to the dealer by calling in the filthy state of your oil.

Under Pressure, You Hope
A flat car tire is never fun. Pete Leonard/Corbis

Tire pressure monitoring (TPM) is one of your basic self-diagnosing systems. In the simplest (read: cheapest) TPM systems, the car will tell you when one of your tires is feeling a little flabby. Not how flabby, or specifically which tire might be having a low-self-esteem day. That's up to you to figure out. Lucky for you, you've only got four choices.

Your more lah-dee-da luxury cars give you much more information. They'll tell you which tire is low and by how much. They'll even draw you a little diagram in the center console screen or right in front of your face in the dashboard. And they'll blink and beep and turn the little diagram an angry red if things get dire.

Your automotive robot overlords are very particular about their continued ability to roll along the road. They're also quite vain. No flabby tires allowed.

Brake It Down
In some cars, sensors will tell you when the brake pads are getting thin and losing their stopping power. Transtock/Corbis

Cars without fancy sensors have a low-tech way to tell you that your brake pads need changing: they squeal like angry piglets. They screech like baby bald eagles waiting to be fed. They scream like your mother did whenever you came home after curfew. You get the idea. It's not pleasant.

But thanks to modern sensor science, your car can tell you when the brake pads are getting thin and losing their stopping power. Better yet, your automotive robot overlords will tell on you. BMWs and Acuras both will use their on-board communications capabilities to call the dealership to tell them that you're a menace to other drivers, and the car fears for its own safety. Or they'll relay a simple code, and the dealer will call to set an appointment at your convenience. Whichever.

Cut the Crud
Diesel fuel spews out a lot of crud, known more scientifically as "particulates." Patrick Byrd/Science Faction/Corbis

As more kinds of fuels become available (besides plain old gasoline) drivers need to get used to entirely new systems and problems. Electric cars are pretty much a bundle of sensors with a body, wheels and seats attached, so when they beep at you, it isn't surprising.

But diesel vehicles have been around for decades. They're solid and familiar and just like a gasoline car, right? Mostly, but diesel fuel spews out a lot of crud, known more scientifically as "particulates." This is why diesel had such a stinky reputation for so long and why the EPA requires particulate diesel vehicles to have filters these days.

It took a lot of technology to get diesel fuel that clean, and a lot of the job is still left to the particulate filter in the exhaust system to keep as much crud out of the air as possible. Since a clogged up filter can't keep the soot out of the air, it has to be changed in order to comply with emissions regulations.

Your car wants to be compliant, so its sensors keep tabs on the particulate filter and it lets you know when it's gotten too cruddy to go on.

I Get Misty
Some cars, like the Acura RLX, can sense the humidity level in the cabin. Frank May/dpa/Corbis

Cars don't just diagnose dangerous things. They can also use their sensors to make your life easier and more pleasant. Without you, who would your automotive robot overlord lord over? It's in the car's best interest to keep you happy.

Take, for example, the Acura RLX, which senses the humidity level in the cabin. If the interior gets too damp, it will turn on the air conditioning and recirculate the air to prevent fog or frost from collecting on the windows.

Now, if the humidity is of a more "steamy" nature, wink wink, the cold blast of air the car sends out of the vents is due to a fit of jealousy. Guaranteed.

Tighten Up
If your check engine light illuminates, try tightening the gas cap. Friso Gentsch/dpa/Corbis

This one has caused nearly every driver to have a heart attack, followed by relief, followed by irritation that lasts for days. The gas cap.

The check engine light comes on while you're driving. Your heart stops. Should you pull over right now? Is a piston about to come flying through the hood? What does your automotive robot overlord want you to do? How do you appease him?

You drive straight to the dealership in a panic. The mechanic takes out his diagnostic device, plugs it into the car's computer and then he gives you the bad news: the gas cap isn't screwed on all the way. You nearly faint with relief that it isn't a $1,000 problem. You wouldn't have lost your life had you continued on your way.

Wait. You wouldn't have lost your life. This was not an emergency. It didn't have anything to do with the engine, which is important. It had to do with the gas cap, which is important, but hardly in the same league.

If you're a BMW driver, your car will give you a bit of a reprieve. If the service engine light comes on and you think, "Huh, I did just get gas. Maybe I'll check that before I continue with my panic attack," and screw the cap on yourself, the light will go off without the assistance of a diagnostic tool to clear the code. Crisis averted.

Fluid Levels
Sensors or not, you can still open the hood and check the dipsticks or eyeball the fluid reservoirs. KidStock/Blend Images/Corbis

There are more fluids in your car than just oil. There's transmission fluid, brake fluid, power steering fluid, coolant and more. You used to be able to check most of these by opening the hood and checking the dipsticks or eyeballing the reservoirs. Actually, you still could, but who has time for that? After all, you want to get home so you can rewatch "Lost" from start to finish and really pay attention this time.

Good news for you. Sensors can easily track the levels of these fluids and let you know when they're low or in need of a change.

Down the Drain
Some new BMW models have sensors that keep track of the drain on the car's battery. They'll even call you if you happen to leave your light on. Linda Patterson/Design Pics/Design Pics/Corbis

Sometimes when your car rats you out to the dealership, it's for your own good. Take, for instance, your habit of leaving your lights on until your battery is dead and you have to call your brother-in-law, the one with jumper cables, who is starting to hate you a little bit because you always call for help just as "The Bachelor" is starting the rose ceremony, and he loves that part.

Luxury car companies such as BMW also like "The Bachelor," and they want you to stay on your brother-in-law's good side, so they've got sensors to keep track of the drain on the battery. If things are looking bad -- again -- the car will, with its last electronic breath, communicate with the dealership rather than your brother-in-law. Then someone from BMW (someone who's probably not all wrapped up in "The Bachelor" at that moment) will give you a call to let you know that you need to shut your lights off.

Breaking and Entering
Stolen cars often end up like this. Joseph Sohm/Visions of America/Corbis

You know, your automotive robot overlord needs you as much as you need him. He acts like he knows so much more than you, and without him you'd be nowhere -- literally -- but he'd like to stay with you. And intact.

Some cars, including some Acuras, can tell when they're being broken into. They sense that someone is tampering with the locks, and instead of going into a full-on freak-out, they quietly, calmly call you.

"Hey, Steve, what's up? It's the RLX. How's your day going? Yeah, Larry sure is a jerk. Hey, listen, I'm down in the parking lot being broken into. Think you could call security or the cops or someone? Thanks, buddy."

If your Acura is actually stolen, it will have a complete meltdown, if you want it to. You can turn on the lights using an app on your phone and track your loveable overlord down, LoJack-style.

Maybe Your Car Doesn't Want You to Die
You definitely don't want this stuff getting into the cabin. Jose Luis Pelaez, Inc./Corbis

You know what people breathe? Oxygen. You know what they exhale? Carbon dioxide. You actually inhale and exhale everything in the air, but these are the important parts. You and trees, working together to keep each other alive.

Speaking of breathing in things you shouldn't, you know what cars exhale? Carbon monoxide and nitric oxide -- two very dangerous things. Breathing these gases will not keep you alive. Cars are not trees.

But cars are not, as we've discovered, evil robot overlords, either. They want you to live! Thus the sensors found in the interior of the Acura RLX that detect the presence of exhaust gases and alert you to the danger. Open all the windows and get thee to a dealership pronto.


The GM Car That Has No Steering Wheel or Pedals

The GM Car That Has No Steering Wheel or Pedals

General Motors has developed a self-driving car called the Cruise AV that has no steering wheel or pedals. Learn more at HowStuffWorks.

Author's Note: 10 Problems Cars Can Diagnose By Themselves

You may wonder how we writers decide who to interview for our articles. The first criteria is that they do the thing I'm writing about, in this case, build self-diagnosing technology into their cars. The second criteria is that they call me back.

In this case, I picked BMW as one of the manufacturers to interview because I had a 7-series test car a couple of years ago that was so sophisticated it made me feel like an extra on "Jersey Shore." Not even one of the stars. It gave me more information than I could ever use about the state of the vehicle, which I promptly ignored. There was information in the dashboard, on the LCD screen -- everywhere. The car was smart.

Turns out it was also trying to tell me I had a flat tire. Like, really flat. It was making it pretty plain, with pictures and yellow and red warning lights and everything. I finally took the car in to a dealership, where they fixed everything right up.

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  • Environmental Protection Agency. "Tools and Resources, Regulator Standards." EPA.gov. (Feb. 14, 2013) http://www.epa.gov/cleandiesel/reg-prog.htm
  • Honda media room. "Acura Debuts Next-Generation AcuraLink Connected Car System at Los Angeles Auto Show." HondaNews.com. Nov, 28, 2012. (Feb. 11, 2013) http://www.hondanews.com/channels/corporate/releases/96912463-d01d-4d7f-9a1d-9cf5d0567133
  • Labrie, Paul. Technical service, electric systems, body and interior manager for BMW. Phone interview conducted on Feb. 14, 2013.
  • Shepard, Tom. Manager, automotive technical operations for Acura. Phone interview conducted on Feb. 14, 2013.
  • Unger, Don. Acura RLX staff engineer for Acura. Phone interview conducted on Feb. 14, 2013.
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