Why Your Car May Not Be able to Start After Jumping another Car?

You might have heard that you risk damaging your car’s electrical system if you use the car’s battery and jumper cables to jumpstart another car that has a drained battery.

While on the other hand, some car owners are able to jumpstart other cars without any problems.

So, where is the problem? Why does it work for some car owners and not others?

So, in this guide, I share some thoughts on why jumpstarting another car can damage your car’s electrical system, how to properly jumpstart a car with a dead battery, and what alternatives are available to start a car with a drained battery without using jumper cables.

Can Jumpstarting another Car Mess up Your Car?

Yes, it is possible for your alternator and ECU of the car used to jump to fail after starting another car.

This can happen because of an excessive current draw on the alternator and voltage spikes induced by the car being started in the electrical system.

Why Jumpstarting another Car Can Damage Your Car’s Electrical System?

When jumpstarting another car using jumper cables, there are risks that the car used to jumpstart is exposed to and need to be aware of in order to avoid them.

Car not starting
Car not starting

#1. Accidentally reversing the polarity of the jumper cables (connecting the positive battery post (car 1) to the negative (car 2) and negative battery post of (car 1) to the positive battery post using jumper cables. This can damage both the ECU and the alternator.

Solution: Double-check the planned cable connections to avoid accidentally reversing the polarity.

You can also purchase cables that have inbuilt reverse polarity protection.

They usually have an audible warning if connected the wrong way and only work when the jumper cables are connected the right way.

#2. High current drain on the starter car alternator and battery. In some cases, the car being jumpstarted can draw high currents more than the jumpstarting car can handle damaging the car alternator in the process.

Lastly, it has been reported that during the process of jumpstarting a car with a drained battery, voltage spikes can be induced in the starting car damaging its ECU (Engine Control Unit) or Engine Control Module.

When the ECU is damaged the car can fail to start, or the engine may run uncontrollably.

Related Topics: Car jumper cables – the 5 things you need to know

How to Jumpstart another Car Safely (Without Damage)

To minimize risk to your car or yourself, confirm that jumper cables are intact without any broken insulation and they are reasonably well-sized (12-16 AWG ) wire before using them to jumpstart another car.

Order of Connecting Jumper cables

1. For the car with a good battery, first, connect the red (positive) clamp of the jumper cable to the positive battery terminal (marked with a + sign).

2. Connect the second red clamp of the jumper cable to the positive battery post of the dead battery (marked with a + sign)

3. Next, connect the black clamp to the negative post (marked – sign) of the good battery.

4. Finally, connect the second black clamp of the jumper cable to the exposed, unpainted part (inside the hood) of the car with the dead battery.

Allow the dead battery to charge for about 5-10 minutes and then attempt to start the car with the dead battery.

The car engine may not start at that first attempt. Allow for another 5-10 minutes and try to start again.

It should start normally at the second attempt.

Let the car engine of the car with the dead battery run for about minutes to charge some more and then disconnect the jumper cables in this order.

To Disconnect the Jumper cables

1. First, disconnect the black clamp of the jumper cable from the exposed, unpainted part (inside the hood) of the car with the dead battery.

2. Next, disconnect the black clamp from the negative post (marked – sign) of the good battery.

3. Then disconnect the red clamp of the jumper cable from the positive battery post of the dead battery (marked with a + sign)

4. Lastly, disconnect the red (positive) clamp of the jumper cable from the positive battery terminal (marked with a + sign) of the good battery.

5. Drive the car which had a drained battery for about 15-30 min to top up its charge level.

Alternatives to Using Jumper Cables to Jumpstart a Car (minimise Risks)

You can use either of these two methods to start a car with a drained battery if you do not want to use jumper cables.

#1. Use a portable jumper box. You can buy a portable jumper starter box that you can use to jump a car with a drained battery in an emergency. These portable jumper boxes are usually easily recharged in under 6 hours using a USB port and are capable of jumpstarting a car between 20-40 times.

Plus, they are able to hold charge for several months (confirm with the owner manual of the jumpstarter box)

#2. Use a car battery charger. A fast battery charger can get your car battery crankable in about 30 min or less.

Final Word

Jumpstarting another car using jumper cables connected to another car can damage the car’s electrical system.

The car’s electrical system may be damaged if you accidentally reverse the battery jumper cables or attempt to charge a deeply drained car battery.

It is important that you follow the correct order of connecting and disconnecting jumper cables to minimize damage to the car’s electrical system.

Related Topics

Leave a Comment