Having your car shut off while driving is a dangerous situation. There are several reasons for this headache. Discover the most likely culprits for random car stalling, how to fix it and avoid it in the future with proper car maintenance, and the steps to take to ensure your safety and that of others on the road when your car shuts off while you’re driving in traffic.
In this article, we will address the issue of the car shutting off while driving. It’s a different matter than 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 causes the idle to drop too low.
7 Reasons Why Your Car Shuts Off While Driving
Faulty Crankshaft Position Sensor
One of the most common reasons for the car stalling problem while driving is a faulty crankshaft position sensor. The role of the crankshaft position sensor is to monitor the many moving parts of the engine, including the crankshaft, engine valves, and pistons. It tracks the speed and location of the crankshaft to facilitate optimal timing of fuel injection and ignition.
In short, this mechanism is essential for optimal engine performance. A failing crankshaft position sensor cannot provide the correct information about the piston positioning in the engine to the engine control unit, causing a cylinder misfire.
If the crankshaft position sensor is not working properly, the check engine light may come on. Another sign that the crankshaft position sensor is faulty is that the tachometer does not work correctly. The tachometer is the gauge usually located next to your speedometer on your dashboard that reads the RPMs in your car. The tachometer usually increases every time you rev your engine. When the intended speed is reached, the tachometer stays in place.
After receiving engine speed information from the crankshaft position sensor, the ECU will then relay the information to the tachometer. So, if the crankshaft position sensor is faulty, it will send incorrect and abnormal data to the ECU, which will then be relayed and cause the tachometer to start erratically or sporadically.
Other common symptoms of a faulty crankshaft position sensor are that fuel efficiency will be compromised and the engine might run very roughly, misfire before stalling completely while driving.
One way to check if your crankshaft position sensor is faulty is to use an OBD scanner and read the error codes from the ECU. If you get diagnostic codes between P0335 and P0338, your crankshaft position sensor has a problem. Although an OBD scanner won’t help you pinpoint the exact problem, it is still a great tool for identifying culprits.
Faulty Engine Control Unit
Another source of problems that can cause the car to stall while driving and the Check Engine light to come on is a faulty Engine Control Unit (ECU) or Powertrain Control Module. Your car’s ECU is a computer that collects information from different parts of an internal combustion engine to ensure that the entire system is working properly, optimally, and accurately to maximize efficiency.
A faulty ECU can cause sudden drops in power, fuel efficiency, and loss of spark, causing your car to randomly stall and restart. Another common symptom of a faulty ECU is your car stalling and jerking while driving. The check engine light may also come on on your dashboard.
Unfortunately, testing and inspecting your ECU is not easy. A check engine light does not necessarily mean an ECU problem. If you want to try to troubleshoot it yourself, the only thing you can do is use an OBD scanner to see what diagnostic code you get. However, the code may still not be clear 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.
Faulty Alternator
Your car’s alternator is responsible for producing a constant flow of electricity from the car’s mechanical energy. It uses this electrical energy to operate various electrical components such as dashboard lights, dome lights, the air conditioning unit, the stereo system, … and to charge the battery. If, for some reason, the alternator is not doing its job properly, your car will not receive the electrical energy it needs, leading to the problem of the car stalling while driving. When this happens, you get a flashing dash.
It is important to note that if your battery is working properly and can step in to provide power after your alternator dies, your car may 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 when running on battery, as the battery is not designed to power the entire car. Once your battery dies, your car stalls and eventually shuts off completely.
If you pay enough attention to how your car is running, you should be able to detect when an alternator is not working properly, meaning your car will start to receive intermittent power. In any case, a basic car maintenance job is to use a multimeter or voltmeter to test your battery with your alternator at regular intervals, say every 4 to 6 months.
To test an alternator, let the engine idle, turn off all lights, including the dashboard, and all accessories like the stereo system that may consume electricity. Perform the battery test with the multimeter. A good alternator should produce between 13.1 V and 14.6 V at normal idle. If not, you should have it further inspected by a professional.
Next, test the alternator to see if it will function properly under heavy use. Have your assistant rev the engine to 2,000 RPM. Turn on all accessories, including headlights, interior lights, radio, windshield wipers… and plug the voltmeter back in. If it reads 13.0 volts and above, the alternator is powerful enough. Anything below 13.0 signals a faulty alternator that needs to be replaced. Make sure you have the best catalytic converters.
Empty Fuel Tank but Faulty Fuel Gauge
You might be surprised to learn that thousands of people every year have their car shut off while driving due to an empty fuel tank. While some may be too busy or forgetful to regularly check the fuel level and refuel as soon as possible, there are cases where your fuel gauge is faulty and does not indicate the actual fuel level in the tank.
One of the common reasons you have a faulty fuel gauge is due to a failure of the sending unit. This will usually cause your fuel gauge to stick in one position regardless of the fuel level, which is usually at the “F” or “E” mark in most cases.
If you think there is a problem with your fuel gauge or fuel level sensor, try filling up 1 gallon or 4 liters of gasoline to see if your car restarts.
Clogged or Faulty Fuel Pump or Fuel System
If your car shuts off while driving but suddenly restarts, it can often be due to a bad fuel pump. Your engine needs a precise fuel supply at a precise time as input for combustion to generate power, and the fuel pump is the part that supplies the engine with the right amount of fuel. If the engine does not receive the right amount of fuel at the right time, the engine stalls, and when this happens, it feels a lot like your car running out of gas. The bad news is that if you are dealing with a faulty fuel pump, there is no workaround for it. You will have to repair or replace it.
Another reason could be that your fuel filter is clogged. The role of the fuel filter is to clean the fuel entering the engine. Over time, it can become clogged with contaminants in old gasoline, so the fuel pump cannot pump the sufficient amount of fuel through it, spoiling the engine’s ability to produce power and shutting off your car while driving.
If your fuel filter is made of nylon or paper, you should simply replace it, which is cheap. If it is metal, you can simply clean it and reuse it.
Most fuel pumps are installed inside the fuel tank. A quick way to check if the fuel pump is really the culprit when your car shuts off while driving is to kick the fuel tank. If the car starts then, there is most likely a problem with your fuel pump. But don’t hit it hard with a metal tool because the tank is plastic and you wouldn’t want to damage it.
Faulty Ignition Switch
When you turn the key to start the car, the ignition switch, which is installed behind the ignition lock, is turned. Inside the ignition switch are many small metal plates that can rust over time. When this happens, one of these plates may lose connection and all contact will be cut off. Or the ignition relay may deteriorate and the mechanism that controls the amount of electricity passing through them will stop working. These will cause the engine to shut off abruptly while driving.
Fortunately, it is quite easy to check if a faulty ignition switch is the reason your car shuts off while driving. When the car shuts off, check if there are still any lights on your dashboard. If the dashboard instrument is dead, a faulty ignition switch is likely. And put your car keys back in the ignition after the car has stalled and try to turn them. If it doesn’t start the engine, you probably have an ignition failure.
Faulty Spark Plugs
The tiny spark plugs are another essential component that allows your engine to generate power. They are the parts that ignite the air-fuel mixture in the engine’s combustion chamber to generate combustions. Each cylinder has its own spark plug.
If you only have one faulty spark plug, you can still start your car and drive. But when more than one spark plug is malfunctioning, your car may start, but it probably won’t run for long. Several faulty spark plugs will cause your engine to stall and shut off while driving.
Before your engine shuts off completely and leaves you stranded, in most cases, there are other telltale signs you need to watch out for, including reduced engine performance, lack of acceleration, engine misfires, and engine knocking.
If you experience these symptoms, it is quite easy to determine if you have a bad spark plug: you just 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 because it overheated or is covered with a substance like oil, fuel, or carbon.
Steps to Take When Your Car Shuts Off While Driving
Needless to say, having your car shut off while you’re driving can leave you stranded in the middle of nowhere or become a safety hazard if you are driving at high speed or on the highway with heavy traffic. Follow the steps below to ensure your safety as well as that of 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 not to panic and guide your car to the side of the road or onto the shoulder. As you slow down to a stop, pull over to prevent vehicles behind you from crashing into the rear, as cars on the highway often travel at high speed. Note that your car will lose the ability to brake and steer, but this is your only course of action.
In the case where slowing your car down is too difficult, try to find a safe spot in sight on the side of the road to guide your car, then engage the emergency brake. This will cause a sudden stop, but it is a hundred times better than stalling abruptly in the middle of the road.
Try to Restart Your Car
Now that your car is safely on the side of the road, the next step is to check if you can restart your car so you can at least get to the nearest auto repair shop. If you are lucky and can determine or narrow down the culprit, you might in some cases be able to get your car started again.
Use Hazard Lights to Alert Other Drivers
But if you cannot restart your vehicle, you must use your hazard lights to inform other drivers that your car is stationary and that you won’t end up in traffic. This will keep you safe while you determine the next steps.
Call Your Emergency Number or a Roadside Assistance Service
When a car is stranded on the road and there is no help in sight, it is 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 reach either, be aware that the police can also help you contact roadside assistance if you have no service or your phone is dead, and they will ensure your car is safe.
And if you are a bit lucky, your car may shut off while driving but restart so you can get home, you can use an OBD2 scanner at the first opportunity to check for fault codes in the engine control unit. Continue diagnosing the fault code if you get one.