1. Dead Battery: This is often the culprit when the engine won’t turn over or start. All batteries will weaken over time. Certain activities can leave the battery undercharged, like infrequent use, a lot of short trips, or using multiple accessories when the headlights are on. Even forgetting to turn off a light or listening to the radio with the engine off can drain the juice out of your battery, making it too weak to start when you need it.
   
   How to prevent it. Although the effect of a drained battery often shows up on cold mornings, it’s the high temperatures of summer that usually do the most damage. So a battery can fail at any time. Be sure to have the battery and alternator tested as part of an annual inspection.
   
   
2. Flat tire or blowout. Flats and blowouts can be caused by road hazards, a tire defect, or lack of care, and can cause you to lose control of the vehicle. If you experience either of these, Consumer Reports recommends taking a firm grip of the wheel and gently guiding the car off the road as soon as possible.
   
   How to prevent it. Many tire problems result from underinflated tires that overheat, due to low tire pressure. Keep all tires, including the spare, properly inflated to the automaker’s recommended pressure by checking them monthly. Also, inspect the tire sidewalls for bulges or cracks.
   
   
3. Fluid Leak. An undetected leak in a critical system can be devastating, possibly resulting in a blown engine or transmission or even brake failure.
   
   How to prevent it. Check the car’s fluid levels regularly, using your owner’s manual as a guide. Look for leaks on the pavement where you park. Black drips are oil; green, orange, or yellow are coolant; and brown or reddish oily drips can be transmission or brake fluid. Any of those can spell trouble and warrant a trip to the mechanic to inspect your car.
   
   
4. Worn out wipers or no fluid. Many accidents are a result of poor visibility. Often drivers don’t realize their wipers are shot or their washer tank is empty until they need them most. And a torn wiper blade can allow the wiper arm to rub against the glass, possibly ruining the windshield.
   
   How to prevent it. Consumer Reports’ auto testers have found that wipers usually degrade in their first six months so it’s best to replace them twice a year. Wipers that have done well in Consumer Reports’ tests include the Valeo 600 Series, RainX Latitude, Anco 32 Series, and Michelin RainForce. Stash spare wiper blades and a gallon of nonfreezing washer fluid in the trunk.
   
   
5. Blown fuse. When a fuse goes, it can disable a critical electrical system, such as the headlights, defroster, or antilock brake system, any of which could lead to an accident.
   
   What to do. You can’t prevent an electrical problem, but a blown fuse should be the first thing you check if one happens. Consumer Reports recommends carrying a selection of spare fuses and a fuse puller in the car. Fuse kits range from $5 to $20 and can be purchased at auto parts stores. Be sure to check your owner’s manual to make sure the fuses you buy are the correct amp rating and size. If the same fuse blows repeatedly, have a mechanic inspect the system.
   
   
6. Broken drive belt. It can disable the car’s water pump or alternator, leading to engine overheating and battery failure. And when it comes to maintenance, belts are easy to forget.
   
   How to prevent it. Consumer Reports advises periodic checks under the hood. If a belt has cracks or the rubber is fraying or feels brittle, it should be replaced. If there’s a lot of slack in the belt, the underside is shiny, or you hear squealing while driving, it should be adjusted or repaired. Most drive belts should be replaced after about 60,000 miles.
   
   
7. Locked out. We’ve all done it. At best, it’s a minor annoyance; at worse, it’s a serious problem when you’re in an unsafe environment.
   
   How to prevent it. Some carmakers provide a valet key or a plastic key for emergency use. If your spare key won’t fit in your purse or wallet, consider a magnetic box for $5 to $10, which you can hide beneath the car or behind the license plate. Often a dealer can cut a door key for much less than a locksmith would charge. Telematics services, such as GM’s OnStar, can unlock a car remotely.

With more than 7 million print and online subscribers, Consumer Reports is one of the most trusted sources for information and advice on consumer products and services. It conducts the most comprehensive auto-test program of any U.S. publication or Web site; the magazine’s auto experts have decades of experience in driving, testing, and reporting on cars. To become a subscriber, consumers can call 1-800-234-1645.  Information and articles from the magazine can be accessed online at www.ConsumerReports.org.