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Why Does My Car Turn Off While Driving?


Why Does My Car Turn Off While Driving?

If your engine shuts off while you’re in the middle of driving, this can be a serious safety issue for both yourself and the other drivers around you. It’s important to properly maintain your car to ensure that you don’t encounter these or any other vehicle issues that could make your car less safe to drive.

There could be several reasons why your engine shuts off on its own while driving. It might be the result of a faulty engine sensor, an issue with your ignition system, a bad alternator, or a problem with your fuel system. It may even be simply that you’ve run out of gas.

In this article, we’ll be covering in detail the reasons why your engine is shutting off while driving, and what you should do if your engine shuts off on you unexpectedly.

Reasons Your Engine May Shut Off While Driving

As we’ve mentioned, there are several different reasons why your engine might shut off on its own, as your car has many components that affect the functionality of the engine. Each of these components has its own set of symptoms when they malfunction, and being familiar with these symptoms can make it easier for you to determine exactly what component has failed.

Let’s take a look at all of the issues that can cause your engine to shut off while driving and go over the various symptoms associated with these issues.

Bad Fuel Pump or Fuel System

Your car’s fuel system is one of its most important components. After all, an engine needs fuel to run, so it’s essential that fuel can consistently make it to the engine. Within your car’s fuel system, the fuel pump is probably the most important part, as this is what actually sends fuel through the fuel lines.

Fuel pumps generally don’t require much maintenance, and it’s not too common for them to fail outright. Nonetheless, this can happen, and if it does, it usually causes a host of symptoms.

Related: How to Start a Car With a Bad Fuel Pump

As you can probably expect, cutting off fuel to your engine can make it turn off suddenly, and this can certainly happen with a bad fuel pump. Even if it doesn’t shut off the engine outright, a failing fuel pump can cause your engine to sputter and run roughly, since it’s not delivering a consistent supply of fuel to the engine.

Other Symptoms Of a Bad Fuel Pump Include:

  • Inconsistent or unexpected acceleration if the fuel pump is sending too much fuel to the engine instead of too little
  • Decreased fuel efficiency, and increased engine temperature.
  • If your engine seems to run fine normally but cuts out when driving hard or hauling heavy stuff, this could also indicate a problem with your fuel pump.

These symptoms could also be the result of other problems with your fuel system. It may be that your fuel filter or your fuel lines are too clogged to allow enough fuel to get to the engine. In such cases, you’ll either need to clean out your fuel lines or replace your fuel filter.

Faulty Alternator

The alternator is another extremely important component of modern cars. Simply put, an alternator is a type of generator used to provide power to your car’s electrical systems and recharge its battery. Alternators are powered by a belt attached to the engine’s crankshaft. 

A working alternator is incredibly important for your car’s functionality, as it provides power to a number of key systems. These include (but are not limited to) your power steering, headlights, power windows, dashboard instruments, windshield wipers, and perhaps most importantly, your fuel pump and fuel injectors.

As we’ve established, if your engine can’t receive fuel, it won’t run, and if the power supply to your fuel pump or fuel injectors is cut off, then your engine is definitely not receiving fuel. 

Fortunately, it’s pretty easy to tell when it’s your alternator that is causing these problems, as a failing alternator has a lot of telltale symptoms. In particular, if your car’s electrical systems are acting up, this is a pretty strong indicator that your alternator is going bad.

If your alternator is failing, it will be providing inconsistent voltage to your various electrical systems.

This can manifest in a few ways:

  • Your headlights might be either too dim or way brighter than normal,
  • Your gauges might not work properly, you might have trouble starting your car
  • Your battery might die for no obvious reason.

In addition, if you hear a whining or growling sound coming from under the hood or if you smell something burning, this could also mean that your alternator is starting to fail.

You might hear these noises if the serpentine belt has become misaligned or if the alternator bearings are starting to wear out, and you might smell burning if the alternator belt or some of the alternator wires are wearing out.

Lastly, a dead alternator will cause the battery warning light on your dashboard to come on. It’s worth mentioning that the battery warning light isn’t used exclusively for battery-related problems; it can come on for a wide variety of issues related to your car’s electrical system.

Faulty Ignition Switch

The ignition switch in your car is a component that doesn’t do too much on its own but is integral to the overall functionality of the car. Your car’s ignition switch is activated by either turning the key in the ignition or, in newer cars, pushing the “start” button.

The purpose of the ignition switch is to activate or deactivate the various electrical systems in your car. These, of course, include basic accessories like your radio and power windows, but also other components of your car that need electricity like your fuel and ignition systems.

This means that if your ignition switch is going bad, it’ll cut power to the various electrical systems in your car, including your fuel and ignition systems. If neither of these systems receives power, there’s no way for your car to run.

Aside from the engine cutting out while driving, other signs of a faulty ignition switch are:

  • If your car suddenly stalls shortly after starting it
  • If the accessories fail to turn on properly when turning the key to the “accessory” position.

There has been a case where the ignition switch has been massively recalled. The most prominent being GM, which in 2014, recalled about 800,000 cars due to a faulty ignition switch, which caused the car to shut off while driving, thereby prevent the airbags from inflating.

This diagram displays the three parts that are affected by the recalls

Some of the cars affected including:

  • 2003-2007 Saturn ION
  • 2005-2010 Chevrolet Cobalt
  • 2006-2011 Chevrolet HHR
  • 2007-2010 Pontiac G5
  • 2006-2010 Pontiac Solstice
  • 2007-2010 Saturn Sky

Failed Crankshaft Position Sensor

While the crankshaft position sensor isn’t the most critical component of your car, it still provides a useful function. More importantly, if your crankshaft position sensor fails, it can cause your engine to suddenly shut itself off.

The purpose of the crankshaft position sensor is to monitor the rotational speed of the crankshaft. This helps the engine control module make adjustments to the ignition timing and the amount of fuel that the injectors send to the cylinders, which in turn helps the engine produce the most power as efficiently as possible.

Crankshaft position sensors generally fail for one of two reasons;

  • The wiring connecting the sensor to the control module wears out
  • The sensor itself is damaged by overheating.

In either case, if the crankshaft position sensor stops working, the engine won’t run nearly as well (and may not even run at all).

A failed crankshaft position sensor can cause your car to stall because it either fails to send a signal to the control module or sends a faulty signal. Regardless of what is going on, if the control module doesn’t detect the right signal from the sensor, it won’t allow the car to run.

Aside from causing your engine to shut off on its own, a failed crankshaft position sensor can also make it much harder for you to start your car to begin with.

Other symptoms of this issue include:

  • Inconsistent acceleration
  • Excessive vibration from the engine
  • Engine that misfires or idles roughly
  • Poor fuel economy.

All of these symptoms stem from the crankshaft position sensor failing to present the engine control module with the right information.

Other Failed Engine Sensors

Aside from the crankshaft position sensor, your engine contains a ton of other sensors designed to collect information to help the car run better. These include:

  • Mass airflow sensors
  • Oxygen sensors
  • Camshaft sensors
  • Exhaust temperature sensors
  • Among several others.

If these sensors go bad, they can also significantly interfere with your engine’s ability to run properly. For example, let’s take a look at mass airflow sensors and oxygen sensors, which are both similar and work in conjunction with each other.

  • A mass airflow (MAF) sensor measures the rate at which air is being drawn into the intake,
  • While an oxygen sensor measures the actual amount of air present in the air/fuel mixture at any given time.

Both of these sensors help ensure that the right air/fuel ratio makes it into the combustion chamber.

If either of these or any of the other engine control sensors fail, it could easily cause the engine to shut off on its own. In particular, a faulty MAF sensor or oxygen sensor can screw up the data that the engine control module receives, causing it to deliver an incorrect amount of fuel.

This can result in an engine that shuts off while driving, as well as several other symptoms:

  • Your engine might run a lot rougher than normal
  • You may notice that your gas mileage has gone way down
  • Your engine might fail to produce enough power, and you may not even be able to start your engine at all in some cases.

In addition, a failed MAF or oxygen sensor will set off the check engine light. Running a scan with an OBD-II diagnostic tool can help you determine for sure if the problem does in fact lie with one of your sensors or something else. 

What to Do if Your Engine Shuts Off While Driving

It’s not too common for an engine to shut off without any warning while you’re on the road, but it does happen every now and then. Fortunately, if you keep your wits about you and don’t panic, this type of situation won’t present you with too much immediate danger.

Here’s what you should do if your engine suddenly shuts off in the middle of driving:

Pull Over Safely

The first thing you should try and do is get off the road as safely as you can. Try not to make sudden movements, as you may not have any power steering, brakes, or turn signals to work with depending on what exactly has gone wrong. Smoothly but quickly pulling over is the best way to avoid an accident in this scenario.

If your brakes have failed, you may have to use the handbrake to bring yourself to a stop, but you should only do so once you’ve made sure you’re out of the way of any traffic coming up from behind you.

Put On Your Hazard Lights

Once you’ve safely pulled over, you should activate your hazard lights if you can. This will let other drivers around you know that you’ve broken down and your car can’t be moved from where it is.

If your alternator has failed, however, then odds are your battery is also dead and you may not be able to activate your hazard lights at all. In this situation, the best thing to do is to open your car’s hood. While this doesn’t provide quite the level of visibility that hazard lights do, popping your hood is a good way to let other drivers know that you’re stranded.

Try Restarting Your Car

Once you’ve done all this, you should at least try to restart your car. Depending on how serious the problem is, you might be able to restart your car and drive far enough to at least get home or to a repair shop. At the very least, this will save you the cost of calling for roadside assistance.

Call Roadside Assistance

If you’ve tried everything you can to restart your car and nothing works, now’s the time to call for roadside assistance. If you have a membership with an auto association like AAA, you may be able to receive free roadside assistance for a number of issues, so if you’re concerned about breakdowns then such a membership can give you a little more peace of mind.

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