What to do if your car shuts off while driving.
Blog/ What to do if your car shuts off while driving.
First, Don’t Panic!
Hopefully, these friendly words of advice will help you on road trips as well as intergalactic travel.
If your car suddenly dies, get it to a safe place, take a deep breath, and try to think about how the car was acting the last 30 seconds before it stopped running, then think about if the car behaved unusually in the days leading up to that point while at idle, high RPM, or under load. Was your car trying to tell you anything? Most of the time, your car will give some signs of what went wrong if you know how to interpret them.
Let’s look at the signs we are given and how we can translate that into possible reasons your car stopped running.
Did the car have any surges, lags, misfires, stutters, hiccups, bangs, or did it just die?
Power surges and lags
Powers surges and lags are often caused by poor fuel delivery. If you are low on gas the fuel will slosh onto and off of the fuel pump until it is finally empty and dies. If the fuel pump itself is failing, it will likely lose pressure at high RPM or under load. Another symptom is it will likely start to make whirring or whining noises but that might only be audible from the backseat or close to the gas tank.
Occasional misfires are likely caused by ignition problems. This could be a fouled spark plug, a bad coil plug/distributor, or a loose connection between them.
Running consistently rough
Running consistently rough with poor fuel consumption is likely a symptom of the sensors that detect airflow or oxygen malfunctioning. When the car is receiving incorrect information about the amount of air it needs, it will miscalculate fuel, timing, and ignition. Depending on the sensor malfunction and the CPU feedback loop it affects, this could be a continuous issue, or it may only affect a certain RPM range.
Clattering and bangs
Clattering and bangs usually indicate a more serious mechanical issue that likely needs professional diagnosis. In many cases, your car could have a blown engine.
Dying suddenly with no warning symptoms tends to indicate electrical issues like bad alternator. , short circuit, or broken connections.
Are there any extra warning lights?
Modern cars have a lot of lights for almost every problem under the sun but there are only a few capable of causing a car to shut off while driving. If there is a check engine light on, have a mechanic read the codes as they will likely provide the location of the failure. Look out especially for ones that look like a battery, thermometer or oil can, as they indicate serious problems?
With the symptoms identified, let’s look at the issues that could be causing them.
Fundamentally, a car needs three things to run. Gas, Air, and Spark to ignite the mixture of the two. If it suddenly dies while running, then one or more of these things stopped working.
The first thing a car needs to run is gas. Assuming there is gas in the tank, then it needs to be transported from the tank to the engine and injected into the engine cylinders for combustion. Fueling problems are often related to dirty gas clogging up a fuel filter or damaging the fuel pump or injectors. Running a car low on gas will increase the likelihood that dirt, rust, or other particulates will be sucked into the fuel system and should be avoided.
Fuel pump failure is a common problem for vehicles with over 100k miles. This can start off with weaker fuel delivery at high RPM and under load leading to loss of power in those situations. It can lead to surging and lagging as the fuel supply becomes increasingly intermittent. These problems can also be caused by a clogged fuel filter.
Fuel Injectors/ Carburetors-
For your car to run correctly, a precise amount of fuel must be combined with air in the cylinder and ignited. Any car made within the last 30 years is going to use an electronic system of fuel injection. Bad fuel injectors might inject too much or too little fuel leading to a wide variety of symptoms including poor idle, misfires, stalls, or poor fuel economy. Problems with the fuel injectors will likely trigger a check engine light with codes to indicate which cylinder is having problems and if that cylinder is running rich or lean. On older cars, this was done with a mechanical system called a Carburetor. Carburetors can easily get gummed up by sitting too long and can be flooded by too much gas.
In order for the gas to burn, it needs to be mixed with air at the correct ratio. Depending on the altitude, car speed, temperature, and humidity the amount of air your car is taking in will vary significantly. Your car needs to figure out how much air is coming in so that it can inject the proper amount of fuel for combustion. To do this your car uses either a Manifold Absolute Pressure (MAP) or a Mass Air Flow (MAF) sensor. If the air intake sensor becomes dirty or damaged it can lead to hesitation, jerking, or stalling during acceleration. Carbureted vehicles use a system of vacuum tubes. Cracked vacuum tubes can lead to rough idle or engine stalling.
Your car also has oxygen (O2) sensors in the exhaust to monitor unburned oxygen concentrations. The O2 sensors communicate with the vehicle’s computer to regulate its engine management. The O2 sensors detecting not enough oxygen means that the combustion mixture is running “Rich”. This means that there is too much fuel being injected for the amount of air. The O2 sensors detecting too much oxygen signifies the combustion process is running “lean”. This can be caused by fuel injectors not squirting enough gas, air intake allowing too much air, or a leak in the exhaust pipe allowing outside air in. If the O2 sensors detect this, they will tell the car’s computer to add more fuel to richen the combustion mixture. If the O2 sensors fail and don’t send any signal, then the car defaults to this action as part of its “Open-loop mode” operation. In addition to physical symptoms of rough idle and loss of engine power, this additional fuel will result in decreased fuel economy, increased emissions, and could potentially foul the catalytic converter.
In order to combust the fuel-air mixture in the cylinder a spark is needed. This spark is created by an electrical current. Sudden failures without warning are often caused by a failure in the electrical system.
The electrical system can be divided into the parts that provide electricity (battery and alternator), and the parts that use the electricity (distributor/coils and spark plugs).
All Electrical power in your car comes from either the battery or the alternator. If either of these fails, then there is no power for the spark plug to ignite the gas and keep the engine running. This will likely be accompanied by a dimmed dash, interior, and headlights. Any time the voltage in the car drops below a specified level it will trigger the battery light.
Car batteries only last for a few years before they lose the ability to hold a charge. However, even if the battery dies, the car should still be able to keep running on power supplied from the alternator. Usually, bad batteries will cause difficulty with starting.
The Alternator is what keeps the car battery charged. If the alternator goes bad, then nothing in the system is charged and the car will only run for as long as the battery can supply power.
A quick way to test if the battery or the alternator is bad is to jump-start the car. Connect the jumper cables to another RUNNINGcar (because you don’t want to kill the car that is saving you) for a solid five minutes to make sure enough charge is transferred. After disconnecting the jumper cables from the other car:
- If your car will keep running for a short period of time and then dies, the battery is good, but the alternator is bad.
- If your car keeps running indefinitely but will not start again, then the battery is bad.
- If the car will start but dies as soon as it is disconnected from the other car, then the alternator and battery are both bad.
Alternators can fail but so can the system of pulleys and belts that are used to turn it. The alternator is powered by a serpentine belt off the engine. If that belt slips, then it could prevent the alternator from turning and generating power. Check that the serpentine belt is on the pully’s and under tension. The alternator then needs to transmit the electricity to the battery and the rest of the car. Check the cables and terminal connections. If they are loose, corroded, or frayed it could cause loss of power or short circuits.
Assuming that we have a proper electrical power supply, it will then be routed through a series of fuses and relays. The fuse box in the engine compartment will contain the fuses to control most of the important functions of the car including the engine control unit. Usually, the lid of the fuse box has a diagram with the functions of each of the fuses. If a short circuit blows a fuse for a vital function it can stop the car dead in its tracks. Check the fuses to see if any of them are blown.
Coil Plugs/ Distributor
Modern car engine computers directly control the spark plug timing by sending electricity to coil plugs to fire the spark plug. Bad coils or bad connections between the coils and spark plugs can lead to misfires and stall the engine.
Distributors make electrical connections to fires the spark plug by a spinning a rotor to make the connection with a wire that leads to each spark plug. Worn out or corroded rotors or caps can inhibit the electrical connections necessary to fire the spark plug.
Spark plugs create sparks by causing an electrical arc across a small gap. Spark plugs wear out and should be replaced every 30K miles or so. They can also become fouled by unburnt fuel and other issues. Occasional misfires will progress to stalled engines.
If your car has shut off while driving following a loud bang or clanging, overheating, or oil loss, then there is a good chance that there is a serious mechanical issue that likely needs professional diagnosis. You should call a tow truck to take you to a mechanic you trust for inspection
Your car can overheat due to loss of coolant, water pump failure, or head gasket failure. Overheating can cause serious issues very quickly. If you see this light pull over immediately to let the car cool down. If a car overheats to the point of stopping the engine is seized and you will need a new engine.
Oil lubricates your engine. If you see this light make sure to stop immediately to add more oil and check for leaks. If the car runs out of oil to the point that it is no longer lubricated and seizes, you will need a new engine.
It is important to know what could go wrong with your car and how to diagnose the problems in order to avoid being stranded. But knowing is only half the battle. The other half is being prepared. Always bring jumper cables, spare fuses, water, and an emergency toolkit in order to fix these common issues. The best way to avoid being surprised by your car dying suddenly is to perform regular maintenance and to pay attention to the little things as they go wrong before they can escalate to a major issue.
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