Car Won’t Start With Jump? Here’s Why

Is your car still not starting even after an attempted jump? Here are the most common causes why a car won't start with a jump and how to fix it.

Jumpstarting can, in itself, be a challenge. You need high-quality leads, an available power supply, and to connect everything up the right way.

But what happens if your engine still won’t start even after an attempted jump? Why won’t it turn over or get going? What if nothing’s happening even while the jumper cables are connected?

In this guide, I will guide you through the most common causes of these issues.

Let’s jump right into it.

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Why Won’t My Car Start With A Jump? Reducing Uncertainty

Businessman turning key to start car engine

It’s possible to definitively say whether there’s an error with the battery, alternator, and/or starter motor. For this, you’ll require a high-quality battery tester.

Do yourself a favor, and buy from your local hardware store. They know what you need. An Amazon purchase is always hit or miss, and when it comes to your car’s electrical system, the last thing you want is a low-quality product. (In a worst-case scenario, this could erase your entire ECU!)

Request the shop assistant to indicate where to find an automotive electrical tester. This will examine the battery, the alternator, and the starter motor.

Once you have it, return to your car. Connect it across the battery (to the correct terminals) and follow the on-screen instructions. If possible, check all three components.

This may indicate that you need a new battery. It could also inform you of deeper problems with the alternator or starter motor. The relevant component(s) must be replaced if the tester tells you anything is operating below its minimum efficiency rating.

The tester might also tell you that all three starting/charging components are working fine. In this case, you’ll know there’s either a severe misfire, a faulty ignition switch, or a problem with the jump-starting process itself.

Is The Engine Turning Over?

First things first. Is the engine cranking (turning over)?

That’s the rrr rrr rrr noise you hear when you turn the key. It might be slow and obviously struggling, but can you hear it at all?

If it isn’t turning over (or there’s only a click), the problem is almost certainly the battery, starter motor, ignition switch, or jumper cables.

If you can hear it, the problem could lie almost anywhere in the starting or ignition systems (including the battery).

The Small Things To Check…

The driver's hand moved the gear selector to the reverse (R) mod

You should check a few things before going to a mechanic and emerging with a red face.

  • Is your automatic transmission in Drive or Reverse? Most need to be in Neutral or Park before the engine turns on, preventing accidental lurching.
  • Have you put your foot on the clutch if you have a manual transmission? Most newer cars come with this safety mechanism. Again, it’s designed to prevent your vehicle from jumping forward.
  • Is your battery connected? Have you been working on the system and forgotten to hook it back up?
  • Do you have fuel in the tank? When was the last time you filled up? There could be an electrical problem with the fuel gauge, too.
  • Does your jump-start power supply have a charge itself? For example, portable battery-powered models might have no power if used recently or left out in the cold.
  • Did you wait long enough to give the jump start a chance to work? Sometimes you’ll be waiting for a few minutes.
  • If you used another car, did you raise its RPMs to 2,000 or so for a few minutes?
  • Diesel engines take a moment to start as the glow plugs warm up, especially on cold mornings. What happens if you hold the key in START another second or two?

If necessary, go back and try again. It makes financial sense to avoid needing breakdown assistance if at all possible.

Whenever you’re attempting a jump start, be very careful. Never do so if it’s unsafe or you’re unsure what to do.

Dead (And Dusted) Battery

battery cables

Note: The engine is unlikely to crank if the battery is badly discharged, but it could. You’re more likely to hear the click of the starter solenoid or nothing at all.

The most likely cause (but far from the only possibility) is a damaged or old battery.

They’re so aged, corrupted, or broken that the chemical reaction to restore a charge imbalance can’t happen anymore.

You’re reversing the discharging chemical reaction when you attempt a jump start. If the engine doesn’t start with the jumper cables still connected, the cells must be in exceptionally poor condition.

The alternator will also be incapable of charging the battery while you’re driving.

There could also be a problem with the battery connections or cables.

How To Fix

You can remedy this problem with a new battery.

This is a job you could do yourself if you choose. Don’t be afraid to ask for assistance from a callout mechanic or a knowledgeable friend, though.

Check your battery type and order the relevant part from a nearby store or for delivery.

Unplug the former one and attach the fresh battery you recently purchased. Make sure you achieve this safely to prevent a brief malfunction. Also, correctly link the terminal units!

There’s no need to attempt a jump start here. The new battery should be fully charged and ready to go.

Does your car start once everything’s connected? If so, excellent!

If your car still doesn’t start, there may be a deeper underlying issue.

At this point, it’s worth having your car transported to your local, trusted mechanic. For someone who doesn’t know their way around engines, it gets quite tricky from here on out.

Poor Quality Jumper Cables

need stylish wire clamps for cars on a white background

Note: The engine is likely to crank. It might not, depending on the severity of the jumper cable problem.

You might find out that the problem isn’t with your car at all. Low-quality jumper leads, clips, or power supply could mean they’re what’s at fault.

In some cases, your car will be just fine. The battery may struggle for natural reasons, such as a cold winter morning.

How To Fix

Try swapping your cables for new ones, especially if they’re getting warm. These are dangerous and should be thrown away.

Connect these across the two cars. Does it make a difference?

You could also try using a different power pack, if applicable. Of course, this only applies if you have a spare available.

Ignition Switch

Car Ignition Switch

Note: You are unlikely to hear anything if the ignition switch is broken. If it’s just damaged, the engine could turn over slowly.

The ignition switch shuts tightly when the key is turned to the BEGIN position in the tube. By shutting, it finishes the connection from the battery to the starter engine.

A broken ignition switch means the current doesn’t ever reach the starter motor. As such, you’ll probably hear nothing at all – not even a click.

This is why a jump start won’t make any difference.

How To Fix

A mechanic will do a like-for-like replacement, swapping out your ignition switch for a new one.

They’ll then attempt to start the car to check if it worked.

Starter Motor And Solenoid

Starter Solenoid

Note: the engine may or may not crank in this case.

The starter motor uses an electrical current from the battery to spin a small pinion gear. This temporarily meshes with the crankshaft’s flywheel and turns it, giving the engine the necessary momentum to start.

A few things could go wrong with the starter motor or solenoid.

  1. The motor itself could have worn out due to wear and tear.
  2. It could have burnt out if you held the key in the START position for too long as the car tried to start.
  3. General damage could have impacted the starter solenoid.
  4. There could be an electrical connection fault at the starter motor.

If your engine is turning over, you can use the advanced tester (mentioned above) to check the starter motor’s condition.

How To Fix

Starter motors are often buried deep within the engine bay. It’s also scarily easy to wire it up incorrectly and cause a short circuit through the car. Get a mechanic to do this one.

They’ll remove it and test all the electrical connections. If it’s deemed unfit for purpose, they’ll order a new part and attach it to your vehicle.

Clogged Fuel Filter

Fuel filter

Note: The engine will crank but won’t start.

The fuel filter does exactly what it sounds like. It removes particulates from the gas or diesel, protecting the chambers from damage.

It should be replaced at regular intervals (but usually not at every service). Most plans recommend a new fuel filter every second, third, or fourth service.

Over time, it will clog up – especially if you’re using poor-quality gas. Know that this usually takes quite some time, though. It’s not the most likely scenario.

The gas or diesel can’t get into the engine with a clogged fuel filter. Thus, it can’t start.

A jump start only charges the battery – it doesn’t affect the fuel filter.

How To Fix

By process of elimination, mechanics might inspect the fuel filter and find it to be clogged up. It’s clear to see and feel when it’s blocked.

They’ll replace the filter with a new part. This should solve your problem.

It’s recommended to leave fuel filter swaps to professional mechanics. While they are usually easy to work on, it’s easy to accidentally get gas or diesel everywhere.

They must also be installed correctly to ensure there are no leaks.

Broken Fuel Pump

Fuel Pump In A Car

Note: The engine will crank after a jump but won’t start.

A broken fuel pump won’t be sending gas to the engine. As a result, there’s no way for it to start.

Pumps do wear out over time. They aren’t a component most people ever even dream about, but they work hard (all the time) throughout a car’s life.

How To Fix

The technicians will replace the fuel pump with a new one. This often involves removing the rear seats or trunk floor.

The new pump must be programmed to match the ECU so the red fuel warning light on the gauge works.

Severe Misfire

Car spark plug replacement. Repairing of vehicle.

Note: The engine will crank but won’t start.

The engine runs via a combination of air, fuel, and a spark. Fuel components, like the pump and filter, have already been mentioned. However, a misfire could be caused by any part involved in the combustion process.

For example, a blocked air intake (improbable) means no air can reach the cylinders. A multi-cylinder coil pack could have failed, preventing the spark plugs from firing. Fuel injectors could be broken, etc.

For a misfire to prevent your car from starting, it is likely serious and probably impacts at least half the cylinders.

How To Fix

A visual examination can only go so far. Mechanics might find clear evidence of fouled spark plugs, for example.

The most thorough inspection will involve OBD II diagnostic tools. These will at least give the technician the relevant cylinders.

The relevant components will be changed. While the engine is being worked on, it’s also a good time to replace your spark plugs.

Car Won’t Start With Jumper Cables: Conclusion

As you can see, there are many possible causes. Thankfully, the most common are also the most straightforward fixes.

Look for an old or damaged battery (using a multimeter or tester) and double-check your jumper cables’ conditions. Never use hot or smoking jump leads!

If the problem lies with neither of these, have your car taken to a nearby mechanic on a flatbed.

Your car won’t start with a jump start if it has a problematic alternator. However, the alternator can damage the battery. Even if your alternator fails, your engine may start with a jump. But it will stop working soon.

You can help prevent starting issues with good general car maintenance. Check your battery and alternator regularly, use high-quality fuel, and take your vehicle for a service when instructed!

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Benjamin Kitchen

Ben is an IMI-qualified light vehicle technician from England with experience in a fast-fit garage. He aims to help drivers worldwide with common automotive problems. You’ll often find him working with his 1.2 Vauxhall Corsa. It may have a tiny engine, but in eight years it's never once let him down!