Why won't your car start in the cold? How winter weather can impact car batteries

Picture this: It's the dead of winter in Chicago, with a cold weather advisory in place, wind chills as low as -30 -- and your car won't start.

Hopefully this isn't a familiar scene. But according to AAA, cold temperatures can leave you with a dead or stressed car battery. A car battery loses as much as 35% of its strength at 32 degrees, and 60% when the thermometer hits 0 degrees, AAA warned.

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"A car battery provides the power to start your car and run some accessories, but it doesn’t provide continual power (that’s the job of the alternator)," a blog from AAA says. "The battery generates electricity using lead-acid technology to create a chemical reaction that turns it into energy. Cold weather can slow this chemical reaction."

AAA also reported that winter weather can exacerbate an aging car battery, leading it to fail. Cold weather can also cause fuel lines to freeze or lead to cold or low engine oil.

If you're unsure if your battery could be in trouble, here are some warning signs, AAA says:

Signs you might have a dead battery

• The battery is more than three years old: The average lifespan of an automotive battery is three to five years. With the increase of electronics in vehicles, this number may skew closer to three years.
• Lights look different: If your headlights are dim and appear yellow instead of white, your battery’s power may be declining. You might also notice that interior dome lights appear dim or flicker, and warning lights may display on the dashboard.
• The car horn sounds strange: When your car horn sounds less emphatic than usual, your car battery could be on the fritz.
• Electronic accessories fail: Signs your car battery is failing include your radio, heated seats, or cell phone charger not working as usual.
• It doesn’t look or smell right: Sometimes, a simple visual inspection or smell test is all it takes to know your battery is in trouble. If you notice a sulfur or rotten egg smell, or your battery is swollen, cracked, or corroded, it may be time for a replacement.

How to prevent a dead car battery in winter

AAA suggests taking proactive steps to avoid a dead car battery in the cold:

• Get your battery tested annually before winter. A battery test can catch a weak battery before it dies entirely. 
• Clean your battery terminals. Corroded battery terminals may prevent your battery from charging properly. 
• Drive for at least a 30-minute stretch once a week. Repeated short trips can drain your battery without giving your alternator a chance to recharge it.
• Park in a garage to protect your battery from the worst of the cold, if one is available.
• If you live in an area with extreme cold, consider investing in a battery warmer or blanket if you park outdoors. 
• Turn off your radio, lights, and other accessories before turning off your car.

What to do if your car won't start

There are a variety of methods you can use to get your car running again, according to JD Power.

• Warm up the battery. You will increase the chances of starting the engine. To do this, you can flash the high beam for 20-30 seconds.
• Turn on the ignition. If you drive a car with an injector, wait a few seconds for the fuel pump to start working.
• Remember to pull the lever if your carburetor has no automatic choke.
• In cars with a manual transmission, before starting the engine, depress the clutch pedal to disengage the frozen transmission from the motor. In vehicles with automatic transmissions, skip this step.
• Try to start the car. The starter should be turned on no longer than 10-15 seconds, as it can overheat. Do it again after 1 minute passes.
• If the starter operates normally, yet the car does not start after three attempts, try depressing the gas pedal and then try starting again.
• If the starter does not turn, the most likely cause is a dead battery or the starter itself.

If those steps don't work, you may need to jumpstart your car, either using jumper cables or a portable jump starter. If you run into car trouble on an Illinois expressway or highway, you can call *999 for assistance.

"After jump-starting the car, drive around for at least 30 minutes to allow the alternator (which powers the vehicle while it’s running) to recharge the battery," AAA said. "It’s always in your best interest to have the battery checked if it dies to ensure the battery is still in working order."

How long should you warm up your car in extreme cold?

While warming up cars for a while during the winter used to be a common practice, that has changed in recent decades.

AAA Automotive recommends drivers only allow their engines to warm up for a short period of time, saying it's a "myth" that warming a car up in cold weather can improve its performance.

"Start the engine and allow it to idle only for the time it takes you to fasten your seat belt," AAA said. "This ensures that lubricating oil gets to all of the engine's vital parts. Driving the car normally and avoiding hard acceleration brings the engine to a warmer temperature faster, and also reduces wear and exhaust emissions."

AAA added that longer idle time in winter is typically OK, as drivers are often clearing snow and ice from the windshield and other car parts.

Excessive idling can take its toll on your engine, experts at Carfax say, affecting the cylinders, spark plugs and emissions system. According to Carfax, idling for longer than 30 seconds could reduce fuel economy and also cause wear on your car.

Is it illegal to warm up your car 'unattended' in Illinois in the winter?

Illinois is one of many states that have implemented laws against leaving motor vehicles unattended, making it illegal to do so.

"...No person driving or in charge of a motor vehicle shall permit it to stand unattended without first stopping the engine, locking the ignition, removing the key from the ignition, effectively setting the brake thereon and, when standing upon any perceptible grade, turning the front wheels to the curb or side of the highway," the state's vehicle code says.

In Chicago, leaving a vehicle unattended is a municipal code violation, as is the case in other communities.

But there is one way around it: Using a remote start.

A vehicle turned on using a remote starter system is not classified as an "unattended motor vehicle," the law says.

The Chicago Police Department has warned against doing so in past years, though, noting a string of vehicle thefts in which offenders targeted unattended vehicles.