Reasons Why Your Car Won’t Start With a Jump

Before we start, let’s explain that if your engine is spinning normally when you turn the key or push the start button, it’s probable that a jump won’t help anyway.

However, the caveat is that there are some platforms that may sound like they’re spinning normally but won’t operate the injectors if the battery voltage goes below about 8 volts. You will probably never see this, but it’s possible.

That said, a ‘no start’ condition can be stressful, especially if you have somewhere important to go. If you’re not new to cars and driving, you’d probably try to jump-start your vehicle. However, this solution doesn’t work all of the time.

But let’s get our terms and phrases right. A “cranks normally but won’t start” situation isn’t a jumper cable situation. But a “slow crank” or “no crank” situation typically calls for an attempted jump.

If you jump the car off and it starts but then dies when you remove the jumper cables, suspect a charging system issue.

Important caution: Always wear safety glasses while working around car batteries–no exceptions. While you never may have seen it happen, a car battery can explode without warning and cause severe eye injury. Keep a pair of safety glasses in your glove compartment all the time. Regular prescription glasses only provide partial protection and won’t stop debris coming in from the sides.

Why Won’t My Car Start Even With a Jump?

There are several reasons why your car won’t start even with a jump. The issue could be caused by a dead battery, loose or corroded battery terminals, faulty jumper cables, a malfunctioning neutral safety switch, a failed power control module, or a  jumped timing belt.

Let’s look at each of them in detail.

Damaged or Dead Battery

Replace your car battery every four to five years. A dead battery won’t be able to supply power to your engine even with the help of a jump.

Cold cranking amps is a good measurable indicator of how much power your battery has to spin the engine, but you need a tool that will measure it. Your replacement battery needs to have at least as many CCA as the original battery.

Cold cranking amps is a good measurable indicator of how much power your battery has to spin the engine, but you need a tool that will measure it.

– Richard McCuistian, ASE Certified Master Automobile Technician

So let’s say your new battery starts out with 650 cold cranking amps. By the time a year goes by, that same battery will usually have only about 550, and after another year you’ll measure about  450 CCA with additional losses every year. You may notice that your engine spins a bit slower on first start then catches and runs. In that case, you need to have the battery checked.

Aside from a completely dead battery, a defective battery is also a problem.

Batteries can short out or become open (opposite problems) without warning. It doesn’t happen on every vehicle or very often, but it does happen.

A damaged battery cell or a short circuit may cause electrical issues which jumpstarting can’t solve. You’ll have to replace your car battery to fix the problem.

Loose or Corroded Battery Terminals

You can also check the condition of your battery terminals. Loose or corroded terminals can disrupt the flow of electrical current to the starter.

Note that even if the terminals look just fine, there can still be a lot of voltage drop (resistance that prevents voltage flow) between the battery post and the terminal even without visible corrosion. GM side-terminal batteries can have a lot of corrosion that is totally invisible.

You can attempt to tighten the clamps or remove the corrosion with a wire brush to solve the issue. You can also try to tighten the bolts. If you’re not into DIY auto repair, you can always take it to the nearest shop.

Jumper Cable Issues

Sometimes the problem can be as simple as a bad jumper cable. A good jumper cable should be well-insulated. It should also have the right length so that it can be properly connected from one vehicle to another.

Also keep in mind that longer cables tend to have more internal resistance, so they might not be able to transfer adequate power to your car. When shopping for jumper cables, make sure to check the specifications of the item you’re ordering.

Bad Neutral Safety Switch or Starter Relay

The main function of a neutral safety switch is to prevent your starter motor from operating unless your transmission is in park (P) or neutral (N). This switch is usually attached to the steering column or on the side of the transmission. Some neutral safety switches simply provide a ground or a signal to the starter relay, which can also be the cause of a no-crank.

PCM Failure

Like any other computer system, your vehicle’s powertrain control module (PCM) can also fail. There can be many reasons why this may happen. For example, power surges or an overloaded circuit can cause PCM issues. If its internal power supply fails, the fuel injectors won’t function, and they won’t be able to supply your engine with the fuel it needs to start.

Timing Belt Issues

Your engine won’t start if the timing belt has failed. If you hear your starter motor engage, but the engine won’t start or if it sounds uneven while spinning, the issue might be related to your timing belt.

Aside from the reasons enumerated above, there can be other issues that can cause a ‘no start’ condition.  Some of these have nothing to do with your charging and ignition systems. Whatever the reason may be, the best course of action is to let a trusted mechanic inspect your vehicle for possible faults once you have difficulty starting your car.

Safety Tips for Jumpstarting Your Vehicle

Jumpstarting your car is easy, and most seasoned drivers know how to do it. However, that doesn’t mean you shouldn’t be cautious when doing it.

Here are some safety tips that you should keep in mind when jumpstarting your car:

Don’t let the cable ends or vehicles touch during a jumpstart. Contact while jumpstarting can be a safety hazard. Make sure that you check the position of your cables before doing the procedure.

Check if both vehicles are turned off. As an extra safety precaution, you can set the parking brakes. Place an automatic in park (P) and a manual in neutral (N).

Read your owner’s manual. Before doing anything with your vehicle, make sure that you consult your owner’s manual first. You’ll be able to locate your battery terminals more easily if you read up on the specifications of your vehicle in the manual.

Ask for help from a professional. If you’re not a seasoned DIYer, it’s always a good idea to seek the help of a professional. There are many ASE-certified mechanics out there who can offer quality service, so you don’t have to worry about anything.