How to Jump-start Your Vehicle
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How to Jump-start Your Vehicle

The last thing you want to hear this winter is the clicking of a weak starter when you’re ready to drive your car. Why does this happen, and what can you do to jump-start your automobile safely?

Why Do Cars Need to Be Jump Started in Winter?

The chemical reactions inside the battery become less active as temperatures drop: at 32°F, the battery is 65% efficient, and at 0°F, it’s only about 40% efficient. Breakdown of the electrolytes and plates inside the battery reduce available power, as do outside factors like corroded battery terminals. The engine itself also takes more power to start due to tighter clearances between cold parts and thicker engine oil.

The end result: the battery may have enough power to start the engine when it’s warm out, but the combination of lower available power and higher power demands from the starter keep the car from starting when temperatures dip.

What Should I Look For when Buying Jumper Cables?

The cables should be at least 12 feet long to reach between vehicles, and the clamps should be large enough to easily grip the battery terminals.

Look for thick wires to help transfer power with less resistance. A lower gauge, meaning thicker wire: 8 or 6 is good enough for most situations.

Some cables have a fault detector that will keep power from being transferred if the negative and positive connectors are hooked together. Spending a few extra bucks on this feature can keep you from causing a short that will do serious damage to your car’s electrical system.

Where Do I Connect the Terminals?

Most cars have one battery located on the driver’s side of the engine compartment, but you may encounter a vehicle with a battery in an odd place or connectors that lead to the battery for easy access from under the hood.

Mercedes-Benz usually places their batteries in the trunk or under the rear seat. Older models may need to be connected to directly, while newer models have jumper connectors under the hood. The positive connector is under a red plastic cover located next to one of the strut towers, while the negative wire is an exposed wire nearby. Chrysler uses a similar system on their products, but these connectors are usually located next to the air box.

On a Prius, the positive connector is located underneath the fuse box cover, next to the driver’s side fender.

Diesel engines usually use two batteries. The positive clamp can be connected to the positive terminal of either battery, although GM recommends connecting to the driver’s side battery on their trucks.

Connecting the Cars

1. Turn off both cars and set their parking brakes.
2. Connect the positive cable to the positive terminal of the assisting vehicle then the positive terminal of the dead vehicle.
3. Connect the negative cable to the negative terminal of the assisting vehicle and a ground point on the dead vehicle. This can be any unpainted, non-moving part like an alternator bracket or a bolt on the block.

Why not connect both batteries directly? Batteries release explosive hydrogen gas when stressed, which can be ignited by the spark from the final connection of the circuit.

Jump Starting

Once the electrical systems are correctly connected, start the assisting car and let it run for a few minutes. Since the dead vehicle’s battery is attached, it will be charged by the alternator.

Turn the assisting vehicle off and remove the key from the ignition, then try starting the dead car. If the car is a hybrid, put the starter in “On” mode: depending on your model, either the engine will start, or, if it’s a Toyota, the display will say “Ready” when there’s enough power to start the engine. If it doesn’t want to start, shut off the dead car, restart the assisting car, and wait a few more minutes.

Once the dead car is running again, disconnect the cables in reverse order.

Why Does My Car Have Error Codes After Jump Starting It?

Running electronics at a low voltage or getting a voltage spike when two vehicle electrical systems are connected can lead to odd sensor readings, making the computer think there’s a fault. This can trigger the “Check Engine” light. Some anti-theft systems can also be triggered by low voltage or a jump start. This may go away on its own or need to be turned off by typing into the stereo or infotainment system.

For Rust and Other Body-Related Problems, Go to Merton Auto Body

In addition to installing new batteries for customers at their request, when doing repairs, we offer a variety of helpful services. If your car suffers from rust from road salt or has autobody damage from a winter collision, you can get it fixed at Merton Auto Body. Our ASE-certified staff receives the latest training through I-CAR, so we always have the latest techniques available to repair your vehicle. Have an insurance claim? Our Autobody Estimating Center will get work approved quickly so you can be back on the road in no time. To learn more, visit our website, at or stop by our Sussex, WI location. We proudly service the Lake Country and Waukesha County areas, including Oconomowoc, Delafield, Hartland, and Pewaukee.


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