Why Does My Car Shut Off While Driving and How Can I Fix It?

This is a nightmare scenario you’re driving along and the car suddenly shuts off on you. What can possibly be wrong? The truth is cars can be complex pieces of machinery and are becoming increasingly so as technology advances.

In this post we are going to look at the possible reasons that a car might shut down mid operation as well as what you might be able to do to fix this problem.

What Can Cause a Car to Shut Off?

We are going to look at a few of the most common causes of a car shutting off suddenly while driving.

Faulty Crankshaft Position Sensor

This is one of the most common reasons a car might shut down while you are driving and it is a sensor based issue. The crankshaft sensor is the problem in this case and as it is a necessary component in making your engine run it’s hardly surprising that it being faulty would cause an issue.

It should be noted that a faulty crankshaft position sensor might not stop the car completely but it would certainly limit the engine activity if not causing it to shut off.

Faulty Fuel Pump or Fuel Supply System

There are three basic requirements to make the internal combustion engine run; fuel, oxygen and a spark. The lack of any one of these will stop the engine or prevent it from starting at all. This is why the fuel pump or fuel supply systems are so important.

The fuel pump supplies a measured amount of fuel to the fuel injectors. If this pump does not supply the fuel then this can cause the motor to turn off which will essentially leave you stranded at the side of the road.

There is no way to bypass the fuel pump so this issue is going to need either a repair or a replacement to remedy. Chances are there will not be a side of the road fix without professional assistance. Sometimes though it might not be the pump but could be instead a fuel filter being clogged.

A clogged fuel filter however would be a relatively easy repair as this is a simple component. When a fuel filter gets too dirty it gets harder for fuel to pass through. Eventually all fuel filters need to be replaced so this should actually be part of routine regular maintenance.

Another sign of a fuel pump that may be breaking down would be the car shutting off suddenly but you are able to restart it again immediately. This should be taken as a warning sign to get that pump checked out because the next time it stops it may not restart.

Empty Fuel Tank

At the risk of sounding condescending we have to mention this option even though we are sure you most definitely know what the fuel gauge is and how to read it. Distraction happens though and you may have been driving for a while and not thought to look at the fuel gauge.

In modern vehicles you often get all kinds of noticeable warnings that your fuel is getting low but you should always keep an eye on how much you have and prepare well in advance for the next fuel stop. If you run out of fuel your engine will simply stop because it no longer has what it needs to run.

It should be noted that there is a possibility that your fuel gauge says you have fuel but you are actually empty. A faulty fuel gauge sensor or fuel level sender might give you a false reading. This is easily tested out by getting a gallon of fuel and putting it in the tank. If the engine starts after this then you have some sensor problems.

Alternator Issues

The alternator is a component under the hood which turns engine rotation into electrical charge with which the car's battery is recharged. It is a constant process when the engine is running but if this alternator suddenly stops working the battery can quickly become drained.

The spark element of the combustion engine comes from the power stored in the battery so if the battery becomes fully drained then the engine stops sparking and it will stop. There are usually warning signs of this issue in the form of the red battery light. This can mean the battery either needs replacing or that it is not being charged by the alternator anymore.

It should be noted that if the alternator is at fault then the car will be completely shut off so not even the dash lights will work. If there is electrical power and the starter motor works then the issue will not be the alternator.

Faulty Ignition Switch

When we engage the car's ignition by turning the key or pressing the button then tiny metal plates make contact within the switch. They remain in contact while the engine is running so if they were to lose contact while you were driving the engine would suddenly stop.

It is possible that corrosion and rust could cause these plates to lose a clean contact which will disengage the ignition. If the dashboard does not show the ignition lights then there is a chance that this could be the issue.

Malfunctioning Sensors

The bane of the modern car is also what makes them so modern in the first place and it is all those clever sensors. The problem is sensors are delicate components and easily become damaged or fail. There are numerous sensors which help monitor air-fuel mixtures, fuel consumption and a whole host of other engine aspects.

One simple sensor could be the reason that your engine shuts off suddenly but will also restart straight away. If the issue is sensor based then a mechanic can read the car's computer using a scanning tool and find out based on error codes which one is at fault.

Fixing a Car That Shuts Off While Driving

A car that randomly shuts off while driving even if it starts back up right away is still a dangerous thing to be driving so you are going to want to stop this situation quickly. In this section we will try and help you find some solutions to this irritating issue.

Check Trouble Codes

Modern cars are designed in such a way as to have most of their faults reported to the vehicle's central computer. These error codes can be easily read using an OBD2 scanning tool which we can actually obtain ourselves if we are technologically inclined.

Mechanics of course have access to much better scanners than the average car owner so if you are not intending to make your own repairs you should get to a repair shop where they can simply plugin to the vehicle and find out which system or component may be at fault.

Check the Alternator

As mentioned the alternator may be at fault here. By starting your engine you can use a multimeter to test the voltage of the car's battery. A reading below 12.5 volts may indicate that the alternator is not working correctly.

Make Sure You Have Fuel

Again, not to question your basic knowledge of car ownership but check that fuel gauge. If it reads empty then the problem is obvious. If it says you have fuel yet the engine is still not firing up it may be worth getting a gallon and adding it to the car.

Sometimes sensors will give you a false reading and tell you there is gas in the tank when in fact it is bone dry. If the car starts after this then you have a sensor issue which you should get fixed soon. No one needs to play the guessing game of how much fuel they have.

Check Your Tachometer

We mentioned the crankshaft position sensor earlier as a possible cause of the engine shutting off. Well there is a clue that you might want to watch out for. If either the crankshaft or camshaft position sensors are faulty the tachometer may not move when your engine is running.

The reason for this is that these sensors report to the tachometer so if they are not sending signals then obviously this will not move or change.

Check the Dashboard

What the dashboard is doing can be a big clue as to what is happening with your car. If for example the dashboard lights go out when the engine shuts off then it may be an ignition switch issue that you are dealing with.

This might also be an indication that the battery and alternator are part of the problem. As mentioned however you will likely see the red battery warning prior to this issue as the battery gradually loses its charge.

Talk to a Pro

We would all love to be mechanical pros when it comes to our cars, it would save so much money. Sadly we are not all technically minded and we should understand our limits. Unless you are sure you can make the fix or diagnosis, leave it to a pro.

Mechanics have the know-how and diagnostic tools to get to the root of the problem. So if you are in any doubt get some professional assistance.

Conclusion

There are several reasons that a car might suddenly shut off on you while driving. Some are easy to diagnose and repair while others are more complicated. There are usually diagnostic clues as to the issue but with so much tech in cars today it might just be an annoying sensor.

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