Why is My Car Stalling While I Am Driving?

Having your car stall on you while driving is not just alarming, but potentially dangerous as well. If you're overtaking a slower vehicle or cruising down the highway at higher speeds, the last thing you want is a car that stalls out of nowhere.

There are several reasons why your car might stall while driving that can include:

  • Fuel Issues
  • Faulty Sensors
  • Ignition System Issues
  • Sensor Issues

Fixing your car and solving the stalling issue could cost you as little as $50 if the problem is something as simple as a filter, or several hundred dollars if you require a fuel pump, an alternator, or something else. This article will go over the most common reasons why your car stalls while driving and tell you how you can fix them.

Charging System Issues

cost to replace the alternator
Replacing alternator.

The alternator is a car component that acts as an electrical generator, converting mechanical energy stored in the battery into electrical energy in the form of alternating current. Your car uses said current to power everything, from replenishing the battery to running the A/C and lighting up the instrument cluster.

The alternator usually provides between 13.5 and 14.5 volts, ensuring normal vehicle operation. A faulty alternator can cause significant voltage drops, sometimes even below 12 volts, which could lead to the vehicle stalling, rapid battery discharge, flickering lights, and much more.

If your car has a faulty alternator, you probably won’t be able to start it up again. Unfortunately, if this happens, you’ll need to get the alternator replaced.

Fuel System Issues

Issues with the fuel system are also relatively common, but sometimes it can be extremely difficult to figure out exactly which component of the fuel system is to blame for the issue.

The fuel system is a complicated network of car components that all work together to provide fuel and, ultimately, enable combustion inside your engine. Issues associated with the fuel system commonly result in loss of fuel pressure.

A clogged fuel filter is the easiest and least expensive component to replace. If your fuel filter is not able to let enough fuel flow through to the engine, simply replacing it might solve the issue.

A more severe issue is a failing fuel pump since they are much more expensive to replace and requires significantly more expertise.

Ignition System Issues

Replacing faulty ignition coil.

Unlike diesel engines which use compression to ignite the fuel/air mixture, gasoline engines rely on a spark plug to set off the combustion cycle.  A faulty spark plug could cause a sudden stall though it will most commonly only result in a cylinder misfire.

Faulty ignition coils, worn-out distributor caps, and severely damaged rotor buttons can all cause spark loss, which as we explained, can lead to a stalling engine. You may experience these issues while driving or when simply sitting stationary when you’ll notice a car stalling at idle.

Sensor Issues

If there’s nothing wrong with your car mechanically, the fault could lie in one of the dozens if not hundreds of sensors scattered throughout your vehicle. The car’s brain, the ECU, relies on data from these sensors to control the engine and prevent catastrophic engine damage.

The most common sensor which can lead to your car stalling is the manifold absolute pressure sensor (MAP) or the mass air flow sensor (MAF). Most cars typically have one or the other.

It’s the MAP/MAF sensor’s job to measure the air density entering the engine and calculate how much fuel should be used to provide the optimal fuel-to-air mixture based on that data. If this sensor fails completely or provides inaccurate data, the ECU can make the fuel/air mixture too lean or too rich, causing ineffective combustion and a stalling engine.

Other sensors which could potentially cause your vehicle to stall include the engine coolant temperature sensor and the throttle position sensor which measures the position of the accelerator pedal.

Although slightly less common, a faulty crankshaft or camshaft sensor could also lead to your car stalling, both while driving or when stationary. Additionally, certain issues related to the idle air control valve (IAC) or the throttle body itself can be the reasons behind stalling the engine.

Vacuum Leaks

Some cars and car systems rely on vacuum to perform their job effectively and as intended. When discussing a vacuum leak, people usually refer to a leak in the intake manifold that brings in more air than the engine can handle or is prepared for.

As you can imagine, an air leak will cause the car to run lean, which means that the mixture inside the engine doesn’t have enough fuel in it to combust as intended. Vacuum leaks are most noticeable at startup, especially in colder climates, where your car wants to run rich for the first few minutes until it gets up to temperature.

Vacuum leaks will give symptoms such as engine misfire, delayed acceleration, and most notably, an extremely rough and choppy idle. All of these symptoms could lead to stalling provided the leak is large enough.

Timing Belt Issues

A person using a serpentine belt tool to loosen and remove the old belt before installing a new one.
Replacing timing belt.

The engine uses a drive belt to power the rest of the components and systems, such as the A/C compressor and the power steering pump. If one of these components locks up or freezes, the drive belt won’t be able to go over the pulley smoothly and it’ll encounter a great amount of resistance.

If the timing belt doesn’t snap, the engine crank pulley will effectively take the brunt of the force, causing your car to run like it has half the amount of horsepower or completely smothering the engine, stalling your vehicle in the process.

Contaminated Fuel

Although extremely rare in this day and age, contaminated fuel is something that could cause your vehicle to stall, especially if you’ve just filled up at a gas station you’ve never used before. More often than not, your vehicle will be able to use contaminated fuel but run a little rougher until the next time you fill up. If the contamination is severe enough, you may need to drain the gas tank completely and fill it up with fresh fuel.

At AutoZone, you can find everything you need to fix your car and prevent it from stalling while driving. From air filters and spark plugs to fuel pumps and timing belts, AutoZone is your one-stop shop for all things automotive.

If the job is too big for you, seek out one of our Preferred Shops to help you do the job.

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Be sure to consult your owner’s manual, a repair guide, an AutoZoner at a store near you, or a licensed, professional mechanic for vehicle-specific repair information. Refer to the service manual for specific diagnostic, repair and tool information for your particular vehicle. Always chock your wheels prior to lifting a vehicle. Always disconnect the negative battery cable before servicing an electrical application on the vehicle to protect its electrical circuits in the event that a wire is accidentally pierced or grounded. Use caution when working with automotive batteries. Sulfuric acid is caustic and can burn clothing and skin or cause blindness. Always wear gloves and safety glasses and other personal protection equipment, and work in a well-ventilated area. Should electrolyte get on your body or clothing, neutralize it immediately with a solution of baking soda and water. Do not wear ties or loose clothing when working on your vehicle.

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