How to Jump a Car

A Step-by-Step Guide on How to Jump-Start Your Car - from Actual Mechanics

Red and black jumper cables on car battery

The sputtering of an engine trying to turn over but not quite catching can be one of the most frustrating car sounds. Here you are, all ready to go in your car, but it won’t start. Whether you’ve left the headlights on all night, or your battery has simply breathed its last breath, you’re in a must-fix situation. Luckily, a simple jump-start will usually get it going. We’ll review how to jump a car below, but first — a few very important safety considerations.

Know This Before You Get Started

“The most important thing to try and avoid when jumping a car is causing a spark near a charging battery or a battery that was just recently charged,” said Evan Pokorny, a mechanic working in Austin, Texas (but known as the “Motor City Mechanic”). “Charging batteries create hydrogen gas which is extremely explosive. So making the last jumper cable connection on the dead car’s engine block is imperative. This insures that if a spark is created, it’s farthest from the hydrogen.”

Pokorny added that while hooking up the cables and laying them on the ground, to be sure not to lay them in a puddle and otherwise keep them away from any moisture.

And if either vehicle’s battery is leaking, don’t attempt a jump and call a pro.

Green car parked on roadside with hood open

How to Jump Your Car

If you’re ultra-proactive, check out your vehicle’s handbook and read up about jumping before you find yourself in the unsavory position of being stuck with a dead battery. And remember that every car is different, so even though you might’ve jumped your old beater back in high school every time it rained, you don’t necessarily know what to do with your current ride.

In order to jump-start your car without a mechanic or roadside service, two things are crucial: another working vehicle, and jumper cables (gauge 6 is standard). Once you have both, you can begin.

A step-by-step jump-start how-to (with advice from Pokorny, Halfords, and Meineke):

  • Park both vehicles facing each other, about 18 inches apart, but never touching. Set each parking brake, put a manual car in neutral and an automatic car in park, and turn off each vehicle (Meineke recommends removing the keys from the ignition, too).
  • Rest the jumper cables on the ground, taking care that none of the clamps touch each other.
  • Open each hood and locate each battery and its two battery terminals. You need to determine which of the two terminals is positive (+) and which is negative (-) on each battery. Each terminal is usually red or black with a plus or minus sign. Wipe the terminals if they’re dirty.
  • Now attach the clamps, following these steps:
  1. Attach one red positive clamp to the dead battery’s positive battery terminal.
  2. Repeat for the functioning vehicle: attach the second red positive clamp to the positive terminal.
  3. Attach one black negative clamp to the functioning battery’s negative terminal.
  4. IMPORTANT: Do NOT attach the second negative clamp to the dead battery’s negative terminal. Instead, attach it to an unpainted, metal part of the vehicle, away from the battery (Meineke suggests a nut on the engine block). Some cars have jump-starting poles, so check your manual. This will ensure a safe jump.
  • For best results, Pokorny recommends wiggling the clamps once they are in position to achieve the best connection. So, without releasing the bite pressure of the clamp, wiggle them slightly so they bite into the metal, with the teeth on the clamps actually cutting into the metal to achieve a fresh clean connection. “It’s also important to note the side of the clamp with the wire attached is the important side that needs the best connection,” Pokorny said.
  • Once any of the clamps is connected to a vehicle, don’t touch the other clamps to anything but the battery terminals or an earthing point. Ensure each of the four clamps is secured on each terminal and that the jumper cables are not laying on any rotating parts of the engine.
  • Start the functioning vehicle. Let it run (charging the other car’s dead battery) for a few minutes (longer if the battery has been dead awhile or is very old).
  • Try starting the vehicle with the dead battery. If it doesn’t work, let the other car charge the battery for another minute or two. You can even rev the engine of the running vehicle, but double check that the vehicle is in park or neutral and that the parking brake is engaged first.
  • Once the car with the dead battery is running, keep it on and begin removing the jumper cables, starting with the negative, black clamps.
  • Do not let any of the clamps touch each other while any one of them is still attached to either vehicle.
  • Take the vehicle with the formerly dead battery on a drive (30 minutes should do it), so the alternator can adequately charge the battery, helping to ensure it doesn’t die again. You might want to consider driving straight to an auto parts store, but then don’t shut off the dead battery when you get there.

To figure out why your battery died, you want to have your battery checked at an auto parts store, not a body shop, says Pokorny. “A parts store will check the charge of the battery, the charging system of the car, and will even charge the battery and re-check it if necessary — all free of charge. They will also sell you a new battery on the spot if needed and install it for free most of the time.” (This excludes cars with remotely mounted batteries.)

Important safety tip: never jump a frozen battery because it can explode. Dead (or flat) batteries freeze more quickly than live ones, so if, for example, you left your car light on all night in sub-freezing temperatures, don’t simply conduct a do-it-yourself jump. Call a professional.

If the Jump Fails

The most likely reason behind a failed jump is the connections on the jumper cables (not the dead battery), Pokorny said. (You can actually successfully jump a car with no battery.) However, you might also just need a new battery. Batteries are past their prime after about four years and long periods of vehicle inactivity can reduce your battery’s life, as can taking a majority of short drives writes How Stuff Works. Take a look at your battery: obvious corrosion means you have a leak, which will shorten its life, too.

Other possible reasons for a failed jump:

  • Insufficient jumper cable connection
  • Starter connection problem
  • Ignition switch problem
  • Fuse problems
  • Vehicle immobilizer
  • Battery corrosion
  • Faulty alternator

Springs inside car

How to Care for Your Battery

How Stuff Works suggests car owners perform some simple battery care to ensure proper working order:

  • If your battery is covered in a case or insulating sleeve, remove it every once in awhile to see what’s going on underneath.
  • Look for buildup around the terminals. You can clean the buildup off with baking soda and water–just remember to use gloves and safety glasses while working.
  • Smell the battery, paying attention to rotten egg odors (sulfur) or the smell of the battery overheating.

Battery maintenance tip: during each oil change and each vehicle inspection, have your car’s battery tested by a mechanic and ask to see the results. Keeping an eye on weak batteries is the best way to ensure you never have to jump your car in the first place.