How to jump-start a car

Step by step, with a jump starter or with cables: where each clamp goes, what order to do it in, and what to do if it still won't start.

If the car clicks, or the dash lights come on but the engine won't turn over, the battery is usually too weak to start it. A jump start gives it enough power to get going. It's safe to do yourself if you take it step by step and connect things in the right order.

Before you start

Turn the car off and take the key out, or turn off the push-button ignition. Turn off the headlights, the radio and the heat. Put on gloves if you have them. Look at the battery: if it's cracked, leaking, bulging or smells like rotten eggs, don't jump it. That battery needs replacing, and jumping it can be dangerous. On some cars the battery is in the trunk or under a seat; then the hood usually has marked jump points, and your owner's manual shows where.

With a jump starter

This is the easier way, and you don't need another car.

1. Make sure the jump starter is off.
2. Clamp the red clamp to the battery's positive (+) post. It's usually the one with a red cover.
3. Clamp the black clamp to the negative (−) post, or to a bare, unpainted metal bolt on the engine.
4. Turn the jump starter on. Most, like the NOCO GB40, show a green light when the clamps are on right.
5. Start the car. If it doesn't start, wait about a minute before you try again, so neither the pack nor the starter overheats.
6. Once it's running, turn the jump starter off, then take off the black clamp first and the red clamp last.

With jumper cables and a second car

1. Park the good car close, but don't let the cars touch. Turn both off.
2. Red clamp on the dead battery's positive (+).
3. The other red clamp on the good battery's positive (+).
4. Black clamp on the good battery's negative (−).
5. The last black clamp on bare metal on the dead car's engine, away from the battery. Not on the dead battery itself: this last connection can spark.
6. Start the good car and let it run for a few minutes, then start the dead car.
7. Take the clamps off in the reverse order: black from the engine, black from the good battery, red from the good battery, red from the dead battery. Don't let the clamps touch each other while any are still connected.

Thin, cheap cables often aren't enough. If you use cables, get heavy-duty ones.

After it starts

Let the car run, then drive it for at least 20 to 30 minutes so the battery can charge back up. A short trip around the block isn't enough. If the battery died for no clear reason, like lights left on, have it tested soon. Many auto parts stores test batteries for free, or a battery tester tells you in a minute.

If it still won't start

• Clicking, but the engine doesn't turn: check that the clamps are tight on clean metal. White or green crust on the battery posts blocks the power; terminal cleaner and a wire brush clean it off.
• Nothing at all, not even dash lights: the battery may be completely dead, or a cable may be loose at the battery.
• Starts, then dies a few minutes later: the alternator, which charges the battery while you drive, may not be working. That's a job for a shop.
• The engine turns over but won't catch: the battery is fine, and the problem is something else, like fuel or spark.

For trucks and big engines, a stronger pack like the NOCO GB150 helps. The NOCO AX65 is a jump starter and tire inflator in one. Our jump starter or cables guide compares them.