7 Reasons Why Your Car Shuts Off While Driving and What To Do

Having your car shuts off while driving is a dangerous situation. There are many reasons for this headache. Learn the most likely culprits for car randomly shuts off, how to fix and avoid it in the future with proper car maintenance, and the steps to follow to keep yourself and others on the road safe when your car shuts off while driving in traffic. 

In this article, we’ll deal with the issue of car shuts off while driving. This is a different matter from when your car shuts off after you stop. This happens when the engine is very sensitive at idle and can be caused by many things, but the most common reasons are a faulty throttle body or a lean fuel mixture that is causing the idle to drop too low. 

car shuts off while driving
A number of faulty parts can make your car shuts off while driving and put you in danger, so regular maintenance is key, as always. Photo credit: SellMax

7 Reasons Why Your Car Shuts Off While Driving

Faulty Crankshaft Position Sensor

One of the most common reasons for the issue of car shuts off while driving is a faulty crankshaft position sensor. The crankshaft position sensor’s role is monitoring the engine’s many moving parts including the crankshaft, engine valves, and pistons. It tracks the crankshaft’s velocity and location to help facilitate the optimal timing for fuel injection and ignition.

In short, this mechanism is essential for your engine’s optimal efficiency. A failing crankshaft position sensor cannot provide the correct information about piston positioning in the engine to the Engine Control Unit, causing a cylinder to misfire.  

If the crankshaft position sensor isn’t working properly, it can cause the check engine light to come on. Another sign that the crankshaft position sensor is faulty is that the tachometer isn’t working properly. The tachometer is the gauge typically located next to your speedometer on your dashboard that reads the RPM’s in your car. The tachometer typically increases every time you rev your engine. When the intended speed is achieved, the tachometer will stay put in its place.

After receiving information about the engine speed from the crankshaft position sensor, the ECU will then relay information to the tachometer. So if the crankshaft position sensor is faulty, it will send incorrect and abnormal data to the ECU, which is then relayed and causing the tachometer to start working erratically or sporadically.

Other common symptoms of a faulty crankshaft position sensor is that fuel efficiency will be compromised and the engine could run very rough, misfire before stalling out completely while driving. 

One way to check if your crankshaft position sensor is faulty is by using an OBD scanner and reading the error codes from the ECU. If you receive diagnostic trouble codes between P0335 and P0338, then your crankshaft position sensor is having a problem. Although an OBD scanner might not help you pinpoint the exact issue, it’s still an excellent tool to narrow down the culprits.

Faulty Engine Control Unit

Another source of problem that might lead to car shuts off while driving and an illuminated Check Engine light is a faulty Engine Control Unit (ECU) or engine control module. The ECU in your car is a computer that collects information from various parts of an internal combustion engine to make sure everything in the whole system is working properly in an optimal and precise manner to maximize efficiency. 

A faulty ECU can cause sudden drops in power, fuel efficiency, and spark loss, causing your car to shut off randomly and turn back on. Another common symptom of a faulty ECU is your car stalling and jerking while driving. The check engine light might also light up on your dash.  

Unfortunately, testing and inspecting your ECU is not easy. A check engine light doesn’t necessarily mean an ECU problem. If you want to try troubleshooting yourself, the only thing you can do is to use an OBD scanner to see what diagnostic trouble code you get. However, the code might still not be clear cut for a failing ECU. Your only option is to take it to a professional mechanic. A mechanic will have the right tools, software, and understanding to diagnose your ECU.

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Faulty Alternator

The alternator in your car is in charge of producing a constant stream of electricity from the car’s mechanical energy. It uses this electrical energy to run various electrical parts such as dash lights, dome lights, conditioning unit, stereo, … and to charge the battery. If for some reason the alternator is not doing its job properly, your car will not get the electrical power it needs, leading to the problem of car shuts off while driving. When this happens, you will get a flashing dash.

It’s important to note that If your battery is functioning properly and can step in to supply power after your alternator dies, your car can still run for a while without an alternator, so you might not realize right away what you’re dealing with.  

But your car can only last a short period while running on the battery, as the battery is not designed to provide power to the entire car. Once your battery dies, your car will stall and eventually shut off completely.

If you pay enough attention to how your car runs, you should be able to sense when an alternator is not working properly, that is your car will begin to receive an intermittent amount of power. Regardless, a basic DIY car maintenance job is to use a multimeter or a voltmeter to test your battery together with your alternator at regular intervals, say every 4-6 months. 

To test an alternator, leave the engine running, turn off all lights, including the dashboard, and all accessories like the stereo that may be using electricity. Perform the battery test with the multimeter. A healthy alternator should produce between 13.1V and 14.6V at regular idle speed. If not, you should have it further inspected by a professional. 

Then, test the alternator to see if it will function properly under heavy usage. Let your assistant keep the engine running at a speed of 2000 RPM. Turn on all accessories, including headlights, interior lights, radio, wipers … and reconnect the voltmeter. If it reads 13.0 volts and above, the alternator is strong enough. Anything lower than 13.0 signals a faulty alternator that needs to be replaced

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Empty Fuel Tank But Faulty Fuel Gauge

You might be surprised to learn that thousands of people every year find their car shuts off while driving due to an empty fuel tank. While some might be too busy or forgetful to check the fuel level regularly and refill at the earliest opportunity, there are instances where your fuel gauge has gone faulty and does not show the real fuel level in the tank. 

One of the common reasons you have a faulty gas gauge is due to a sending unit failure. This will typically cause your fuel gauge to get stuck in one position regardless of the fuel level, which is typically at the “F” or “E” mark in most cases. 

If you suspect that there is a problem with your fuel gauge or fuel level sensor, try to fill 1 gallon or 4 liters of gasoline to see if your car starts again.

Clogged or Faulty Fuel Pump or Fuel System

If your car turns off while driving but then turns back on suddenly, it can often be due to a bad fuel pump. Your engine needs a precise supply of fuel at a precise time as input for combustion to generate power, and the fuel pump is the part that supplies the engine with the correct amount of fuel. If the engine does not get the correct amount of fuel at the right moments, the motor will shut off and when this happens, it is very similar to your car running out of gasoline. The bad news is if you are dealing with a faulty fuel pump, there is no bypass for it. You will have to fix it or replace it.

Another reason could be that your fuel filter got clogged. The fuel filter’s job is to clean the fuel that goes into the engine. Over time, it can be clogged by contaminations in old gasoline, so the fuel pump can’t pump the sufficient amount of fuel through it, messing up the engine’s ability to produce power and make your car shuts off while driving. 

If your fuel filter is nylon or paper, you should just replace it, which is cheap. If it’s made of metal, you can just clean and reuse it.

Most fuel pumps are installed inside the fuel tank. One quick way to check whether the fuel pump is really the culprit when your car shuts off while driving is to give the fuel tank a kick with your foot. If the car starts then, there is most likely a problem with your fuel pump. But do not knock it violently with a metal tool as the tank is made of plastic and you would not want to damage it. 

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Faulty Ignition Switch

When you turn the key to start the car, the ignition switch, which is installed behind the ignition lock, gets turned. Inside the ignition switch are many tiny metal plates that can build up rust over time. When this happens, one of these plates may lose connection, and the whole ignition will get switched off. Or the ignition relay can go bad, and the mechanism which controls the amount of electricity going through them will stop working. These will cause the engine to shut off abruptly while driving. 

Luckily it’s pretty easy to check whether a faulty ignition switch is the reason for your car shuts off while driving. When the car shuts down, check if there are still lights on your dashboard. If the dashboard instrument is dead, a faulty ignition switch is likely. And put your car keys in the ignition again after the car shuts down and try turning them. If this doesn’t start the engine, then you most likely have an ignition failure.

Faulty Spark Plugs

foul spark plug
On the left is a functional, intact spark plug, and on the right is a foul or faulty spark plug. Photo credit: CarCareHunt

Another vital component that allow your engine to generate power is the tiny spark plugs. They are the parts that ignites the air and fuel mixture in the engine combustion chamber to generate combustions. Each cylinder has its own spark plug. 

If you have only one faulty spark plug, you can still start your car and drive. But when more than one spark plugs malfunction, your car may start, but it most likely won’t drive long. Multiple faulty spark plugs will cause your engine to stall and shuts off while driving.

Before your engine completely shuts off and leave you stranded, in most cases, there are other telltale signs that you should look out for, including reduced engine performance, lack of acceleration, engine misfires, and engine knocking.

If you come across these symptoms, it’s pretty easy to determine if you have a bad spark plug: you jus need to locate and inspect them. Once you can physically see your spark plugs, you can determine the condition of your spark plugs. A bad spark plug is one that is blistered from running too hot, or one covered with a substance like oil, fuel or carbon.

The Steps To Follow When Your Car Shuts Off While Driving

Needless to say, having your car turns off while driving might leave you stranded in the middle of nowhere, or become a safety hazard if you’re driving at high speed or on the highway with a lot of traffic around. Follow the steps below to maintain the safety of yourself as well as other vehicles on the road:

Pull Your Car Over To The Side Of The Road 

The very first thing you need to do when your car shuts off while driving is to try to not panic and guide your car to the side of the road or the shoulder. As you’re slowing down to a stop, pull over to prevent any vehicles behind crashing into your rear, as cars on the highway often travel at high speed. Note that your car will be losing the ability to brake and steer, but this is your only course of action.

In the case that slowing down your car is too difficult, try to find a safe place in sight off to the side of the road to guide your car to, and then engage the emergency brake. This will cause an abrupt stop, but it’s a hundred times better than abruptly stalling out in the middle of the road.

Try To Restart Your Car 

Now that your car is safe off the side of the road, the next step is to check if you can restart your car so that you can at least drive to the nearest auto repair shop. If you’re lucky and can determine or narrow down the culprit, you might in some cases be able to make your car restart. 

Use Emergency Flashers to Alert Other Drivers

But if you can’t restart your vehicle, then you need to use your emergency flashers to notify other drivers that your car is immobile and you will not be merging back into traffic. This will keep you safe while you’re figuring out the next steps. 

Call Your Emergency Number or a Roadside Assistance Service

When a car is stuck on the road and there is no help in sight, it’s best to seek help from an emergency number or a roadside assistance service like AAA, which usually have 24/7 assistance. Alternatively, if you cannot get a hold of either, know that the police can also help you contact roadside assistance if you don’t have service or your phone is dead, and they will make sure that your car is safe. 

And if you’re a bit lucky, your car might shuts off while driving but starts again so that you can get home, you can use an OBD2 scanner at the earliest opportunity to check for any trouble codes in the engine control unit with. Continue the diagnostics of the trouble code if you get any.