How to Jump Start a Car

by Richard Rowe
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Victor Holguin/Demand Media

Like doing a wax job or changing your first flat tire, learning how to properly jump-start a dead battery has become a kind of rite of passage into automotive maturity. Try as they might to keep us in the driver seat and out of the engine compartment, no manufacturer yet has figured out how to build a car that simply cannot deplete its electrical supply. Call it a talent of mental distraction -- people are just very good at killing batteries. Just connecting two cars together with a pair of jumper cables requires little more aptitude than killing the battery in the first place; but doing it properly and safely requires a somewhat more deliberate approach.

Step 1

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Remove or secure loose clothing: scarves, hanging jewelry, etc. You'll be working in close proximity to moving engine parts -- be careful. Pop your dead car's hood and locate the positive and negative battery terminals. Most of the time you'll find them on the battery itself, but some vehicles, like the Chrysler 300, Prius and any number of BMWs, have batteries hidden elsewhere in the car. In these cases you'll typically find stand-alone terminals under the hood. The positive terminal, denoted by a "+" symbol, typically has a red cap or cover; the negative, with a "-" symbol, uses black. If you can't find them, check your owner's manual or look near the main fuse box. Manufacturers typically place positive jump terminals right next to them.

Step 2

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Check the location of the terminals in the donor car, and have its driver park so that his battery terminals or jump posts are within cable-reach of your own. Many a has parked the donor car near their own before bothering to figure out where the terminals were, only to find the cables were too short to reach or had to be routed near moving parts. Parking nose-to-nose is usually ideal when possible; just make sure to leave a foot or so space between the vehicles so you can get by. In any case, do not let the two vehicles touch each other. With the vehicles parked and both engines off, remove the plastic or rubber protective covers from the battery terminals or jump posts. Keep track of the positive and negative posts if they're not clearly marked. Unplug all electrical accessories like cell phones, aftermarket nav systems and MP3 players from both vehicles; the power surge from jumping can easily fry delicate circuitry. Turn off all accessories and lights, except flashers if you need them for safety. Turn both ignition keys to the "Off" position.

Step 3

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Sort out your cables. Double-check that they'll reach their respective terminals without getting anywhere near fans, belts, pulleys or hot exhaust manifolds, and where you won't have to reach across moving parts to connect them. Reposition the donor car, if necessary. Keep in mind that electric cooling fans can come on at any time, for no apparent reason. Follow this sequence of attachment exactly: First, connect one end of your -- typically red-marked -- jumper cable lead to the positive terminal or jump post on the donor car, and then connect the other end to the positive terminal or jump post on the dead car. Hold an end of the black or negative cable in each of your hands, to keep one end from accidentally touching either chassis. Connect one side to the negative terminal or post on the donor car.

Step 4

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Last, connect the other end of the negative cable to a solid metal engine bracket, to an unpainted metal chassis component, or to the separate negative jump post on the dead car. Don't connect directly to the negative battery terminal. This is the final connection, and there will be sparks just as the cable is connected. A spark in this pocket of gas could turn your battery into an acid bomb. Given that, it should also go without saying: Don't smoke while you're doing this.

Step 5

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Have the donor car's driver start his engine and briefly rev it up to about 3,000 rpm. Some vehicles use alternators that don't energize until the engine reaches a certain speed -- usually 2,000 to 3,000 rpm. Failing to energize the alternator could drain the battery on the donor car. Allow the donor car to idle for about 10 minutes. Keeping the donor car's engine at about 2,000 rpm can speed things up in some cases, but revving any higher than that is just wasting gas.

Step 6

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Turn the dead car's ignition key to the "On" position, and check your interior and dashboard lights. They should be bright and steady, and shouldn't get markedly brighter or dimmer if the driver of the donor car revs his engine. That's when you know your battery is approaching sufficient starting charge. Close the doors and turn all the lights off. Don't touch the brake if you don't have to. Attempt to start the car. If the starter chugs, and sounds sluggish or slow, give the battery more time to charge. Don't waste the charge you've built up by trying to start an engine that doesn't have the juice yet.

Step 7

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Wait. Be patient. Try again. If you've given it enough time, the dead car should start. Have the driver of the donor vehicle shut off his engine, and remove the cables in the reverse order of installation: First the negative or ground cable on your car, then the negative cable from the donor, the positive cable on your car, and finally the positive cable on the donor car. Replace all of the plastic or rubber terminal or jump post caps, and shut the hoods. Allow your car to idle for at least 15 minutes, or drive it for that same amount of time.

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