Car Won’t Start With a Jump? Here’s What It Could Be

We’ve all been there before. You get in your car and turn the key, but nothing happens. As an experienced driver and car owner, you know to reach for your jumper cables to get your engine running again. But what do you do if your car won’t start with a jump?

Why Your Car Won’t Start With a Jump

There are many possible reasons your car won’t start with a jump, and some are easier to fix than others. Here are some of the most common causes to help you understand what’s going on with your engine.

Improper Jumping

The most straightforward reason your car may not jump-start is user error. Mistakes are easy to make and even easier to miss. You or another driver might’ve placed the clamps on the wrong terminals. Alternatively, a clamp may be on the negative terminal of the dead battery instead of another metal surface.

Sometimes, it may take a few tries for a jump-start to work, so you may only need to give it another go. The jumper cables you should keep in your car may also have an issue, like faulty wiring or corroded clamps, which could stop them from working properly.

Dead Battery

A dead battery is another common reason a car won’t start with a jump. While a jump-start can bring a nearly dead battery back to life, it needs a little juice left to work. Batteries also have a limited life span, which factors like extreme cold can shorten, so this is a fairly common problem.

Other battery problems can stop a jump-start from working, too. The battery terminals may be corroded, which will render your jumper cables useless even if there’s still enough left in the battery for a jump. Alternatively, the terminals or other connections could be loose.

Alternator Issues

If it’s not a battery problem, it could be something with your alternator. The alternator recharges your battery to make up for the energy you lose starting your car and running the electronics without the engine on. If it’s not working, your battery may not get the power it needs to start your car, even with a jump.

Alternators normally last longer than batteries, but they’ll still degrade over time. You can normally expect them to last between around six to 10 years or roughly 80,000 to 150,000 miles.

Bad Starter

Your car’s starter is another component that can stop it from jump-starting. The starter is a small gear that initially cranks your engine before it can start running on its own power. It also requires a lot of electricity to work, which is why your battery may have enough juice for your lights but not to start your car.

If your starter isn’t working properly, your car won’t start regardless of how much power your battery has. These issues aren’t as common as battery or alternator problems, but they can still happen.

Safety Switch Failure

If you, like 97% of American drivers, drive an automatic, a faulty safety switch could be why your car won’t jump-start. This switch keeps your vehicle from starting if it’s not in park or neutral. Consequently, if it’s broken, your car may think it’s in another gear, stopping it from starting even if everything else is working.

Fuel Pump Failure

Without fuel, the engine won’t start. If the fuel pump fails and the gasoline can’t make it from the tank to the engine, the car won’t start, and jumper cables won’t make any difference. 

What Causes Batteries to Die?

The average car battery will last between three and five years under the hood. Other than age, what causes batteries to stop functioning and leave you stranded?

Deep or Frequent Discharges

Automotive batteries can discharge now and then, but running them empty and recharging them will shorten their lifespan. 

Extreme Heat

Lead-acid automotive batteries use a diluted acid as their electrolyte. Exposure to excessive heat can cause the water to evaporate, which will weaken its charge and can cause the lead plates to rust as the acid gets replaced with oxygen. 

Extreme Cold

Automotive batteries lose much of their starting power when they get cold. Once it gets to 0 F, it can lose up to 50% of its power. Exposure to cold weather can also decrease the lifespan of the battery.

Excessive Vibration

Automotive batteries can withstand some vibration, but they can handle only so much. Too much vibration can cause the cell connectors to break apart, interrupting the circuit and causing it to stop charging. 

Fast Charging

Waiting for a discharged battery might take a while, but running a fast charger too frequently can damage the internal components and shorten the battery’s lifespan.

Overcharging

The very best outcome from overcharging is just a dead battery. The other potential side effects can be downright dangerous. Overcharging your battery can boil the acid electrolyte mixture. The heat causes the water to evaporate and, in extreme cases, can even melt or warp the battery case. 

Testing Your Battery

There are two different ways to test your battery. The first requires a multimeter, which you may already have in your garage. The second requires a load tester. If you don’t have one of these, you may be able to get your local auto parts store to test your battery for you. 

For the first test, set your multimeter to volts and touch the sensors to the positive and negative terminals of the battery. You should see a reading of 12.6 volts in a properly charged battery. Anything lower than that could indicate a problem. If you drop below 12 volts, the chances are pretty high that the battery won’t start the car. Once the vehicle starts, the multimeter reading should be between 14.4-14.6 volts if the alternator is functioning properly. 

The second test puts the battery under a load to simulate when the car starts. From the 12.6 volt baseline, your battery shouldn’t drop below 12 volts when placed under a load. Even if the battery starts the vehicle, a low reading could indicate a dead or dying cell and might tell you that the battery needs replacement. 

What to Do if Your Car Won’t Start With a Jump

Now that you know what may keep your car from starting, it’ll be easier to find the solution. If your car won’t start with a jump, here’s what you can do.

Make Sure You’re Jumping It Correctly

First, make sure you’ve set the jumper cables up correctly before assuming it won’t jump-start. Check that both cars are in park or neutral, the positive terminals are connected and you’ve joined the negative terminal on the good battery to a non-battery piece of metal on the dead car.

Let the working car run for a few minutes before trying to start the dead one. You may also have to try jumping a few times before it works.

Troubleshoot Common Issues

If you’ve followed all the steps correctly and it’s still not working, check your jumper cables for corrosion or other damage. Next, look at the dead car’s battery to see if there’s any corrosion on the terminals. If there is, try cleaning it off before jumping it again.

If you hear any clicking or grinding when you try to start your car, it’s likely a problem with the starter. If you’ve noticed other problems with the electronics in your vehicle beforehand, it’s probably the battery or alternator.

Take It to a Mechanic

If you can’t get it started, it’s time to turn to the professionals. You may need a new battery, alternator, starter or other parts. Write down any issues you’ve noticed, like unusual noises or flashing lights, as these will help your mechanic narrow down the problem.

You can start your car without jumper cables a few different ways, which will help you get going so you can drive to a repair shop. If that doesn’t work, call for a tow to take it to a garage.

Keep an Eye Out for These Issues

It can be frustrating when your car won’t start with a jump. But if you know what could cause it, you can address the situation calmly and effectively. It may take some work, but you’ll get your engine running the way it should again.

Originally posted 2/16/13 – Updated 3/20/24