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How To Jump-Start a Car

Staying safe while connecting cables

(updated February 24th, 2022)

A dead car battery can leave you stranded and be a real headache. But if you carry jumper cables or a jump box in your trunk and know how to use them properly, your problem is solved. Once your engine is running, and if the battery is still good, the alternator will recharge it. If the car battery is bad, at least you can drive to an auto parts store to buy a replacement battery. Often, stores will install a car battery for free.

Jump-starting a car is easy, but you should do it with caution. Since the car battery is located in the engine compartment, where flammable gases may be present, a spark could set off a fire. So while you're hooking up the weak battery to the live battery in the booster car, you'll want to do it without creating any sparks. Connecting the jumper cables in the right order will minimize the chance of sparking. With this in mind, here is a step-by-step guide to jump-starting a car.

It's important to make sure the metal ends of the jumper cables do not touch each other or any metal surfaces on the car until they are connected to the correct battery terminals. This is more difficult than it sounds. Under the hood, most areas are metal. If two people are available to jump-start a car, one person can simply hold the ends of the jumper cables safely separated while the other person moves between the cars, making the proper connections. One person can jump-start a car, but it requires close attention.

If possible, consult your car's manual for the correct order in which to connect the jumper cables. There may be variation among different car makes. Below is the most universally accepted method for jump-starting cars:

1. Select a good pair of jumper cables or a portable jump starter and carry them in your car. The cables should be thick, with adequate insulation and clean metal clamps. In some cases, the cables themselves will come with a chart reminding you of the proper order in which to connect them. If you have a portable unit, make sure its battery is fully charged before storing it in your car.

2. Open the hood of each car to locate each battery and its terminals. In some cases, the battery itself may be hidden, with remote positive terminal (+) and negative terminal (-) posts provided for jump-starting instead. Some vehicles may have a remote negative connection, even if you can access the battery. This is for the final connection that we'll learn about later. Those with a portable jump starter can skip to step four.

3. Park the vehicle with the good battery close to the one with the dead battery, but leave yourself just enough room to walk between them. As you are hooking up the jumper cables, make sure the metal ends of the cables don't dangle into the engine compartment, where they could get caught on such moving parts as a belt or a fan, or on the outside of the car, where they could scratch the paint. Turn off the ignitions in both vehicles, set the parking brakes and make sure that the vehicles are in either park or neutral, depending on whether they have automatic or manual transmissions. Turn off all accessories, such as the lights and radio. If the vehicles are parked in a safe area, turn off the hazard flashers too.

4. Clamp one of the positive (red) jumper cable ends to the dead battery's positive terminal. Be sure the clamp "bites" onto the battery terminal to provide a strong electrical connection. If there is corrosion on the terminal, twist the jaws of the clamp until it cuts through the corrosion and into the metal. Before moving to the other car to make connections, make sure the matching negative (black) cable clamp is not touching any metal surfaces. Those with a portable jump starter can skip to step seven.

5. Clamp the other end of the positive jumper cable to the positive terminal in the booster car. Again, confirm that a plus sign is next to the battery terminal. Connect the negative cable end to the negative battery terminal in the booster car. Now that the negative cable is connected to the battery terminal, you can attach the other end to an unpainted metal surface on the engine of the car with the dead battery. If a labeled remote negative terminal is available, use it. Otherwise, find an unpainted bolt or bracket that is at least several inches away from the dead battery. This will provide a solid ground and further reduce the possibility of sparking.

6. Make a final check to confirm that the jumper cables are not near any moving engine parts and then start the booster car. Let it idle for several minutes to build up a sufficient charge to start the other car's dead battery. If the dead battery is new and was drained by the car lights being left on for an extended time, it will probably start quickly. If it is an old battery or if the car sat without starting for a long time (more than a month), it may take longer for the battery to charge and start. It sometimes helps to rev the engine in the booster car a little to hurry the process along.

7. Start the vehicle with the dead battery and idle for a few minutes. If the vehicle won't start but it does crank quickly, then look for other problems, such as an empty gas tank.

8. Carefully disconnect the jumper cables, reversing the connection order. The first cable you remove (the negative terminal that's attached to the formerly dead battery) is the most critical. Make sure your helper holds the cable away from any metal or the other cable ends while you disconnect the others.

9. Drive the jump-started car for at least 20 minutes so its alternator can recharge the battery. Make sure you are somewhere safe before shutting off the engine because, depending on the battery's condition or the health of the alternator, the car might need to be jump-started again.

10. If the battery that you've jump-started is more than 3 years old, consider having it tested at an auto parts store. If other problems in the car caused the dead battery, take the vehicle to a mechanic for an inspection.

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