How to Diagnose & Fix a Car Stalling

It’s happened to many of us before and it’s extremely frustrating: Having your car stall. Few things are as aggravating as car problems, and unfortunately, a car stalling is one of the more common automotive issues. In general, a car needs three items to successfully start and run: air, fuel, and spark. If any of these components become compromised your engine is susceptible to stalling, and it’s not always easy to find the cause. Is your car stalling or did your engine die and refuse to restart? 

We’ve got you covered. Read on to learn all of the most common causes for why a car might stall, as well as a few solutions to get you started on any possible fixes and repairs. 

Most Common Causes for a Car Stalling

Before we start, it’s important to keep in mind that there are dozens and dozens of things that could cause a car or truck engine to not start. These range anywhere from no gas or bad gas, to a faulty alternator, to potentially even a broken timing chain or clogged intake filter. The possibilities are almost endless. 

In this article, we’re just going to go over the five most common causes of engine stalling. As well as potential fixes. If you go through our list and still find yourself with an answer, it might be best to have a qualified mechanic take a look. Keep in mind, the three things every engine absolutely needs are air, fuel, and spark. If you can verify all three of those systems are working your issue is probably more complicated and technical. 

Let’s take a look at the five most common causes of a car stalling.

Cause #1 for Why Your Car Stalls – Alternator

One of the most common causes of a car stalling is due to a faulty or failing alternator. The alternator is responsible for turning mechanical energy into electrical energy. It’s a very important part and does things like recharges the battery and powers the windows, infotainment systems, and even the headlights and brake lights. Without your alternator many of the accessories in your car wouldn’t work, additionally, your car wouldn’t start.

A bad alternator is bad news for the ignition system. Alternators help engines start by supplying voltage to the ignition coils. The ignition coils send voltage to the spark plugs, which is what provides the “spark” for an engine to combust. If the alternator is failing or dead, the ignition coils won’t receive enough voltage. This means they won’t be able to give the spark plugs enough voltage, As a result, they will either fail to fire or won’t fire enough for full combustion.

Symptoms of a Bad or Going Bad Alternator 

Some of the most obvious symptoms of a bad or going bad alternator are:

• Engine fails to start
• Car dies while driving
• Car stalling
• Dead battery from not recharging
• Dim or flickering headlights or cabin lights
• Low or malfunctioning electronics, windows, infotainment systems
• Lack of spark from spark plugs

There are many potential warning signs that your alternator is going south, though they can die unexpectedly. Generally, drivers can expect alternators to last anywhere from 75,000-150,000 miles or 6-10 years on average. If you know your alternator is getting up there in age and you’re starting to have the above problems, it’s a good place to start looking. 

Replacing the alternator is relatively straight forward, but also involves replacing the engine’s serpentine belt at the same time. Typically, a new alternator will run around $150-200 for a non-OEM replacement. Though it’s closer to $400-500 for an OEM replacement. 

Cause #2 For a Car Stalling – Fueling System

After an alternator, one of the most common causes of a car stalling is the fuel system. Granted, the fuel system includes many different items and is relatively broad. However, any links in the fuel chain that are compromised can disrupt the entire system. Some of the most common parts of the fuel system are the fuel injectors, fuel pump(s), carburetor on 1980s and earlier engines, fuel lines, fuel filter, and the fuel itself, gasoline. 

When your car is running, your ECU (engine control unit) controls how much fuel is delivered from the fuel injectors into the intake runners (or directly into the combustion chamber if your car is Direct Injected). If there is a problem in the fuel system, your car will struggle to maintain the correct air-to-fuel ratio. This can lead to reduced gas mileage or damaged piston rings if the mixture has too much fuel. Or it can lead to detonation and pre-ignition, and potentially even melted pistons, if the mixture has not enough fuel. 

If there is not enough fuel or your cylinders are flooded, your engine is susceptible to stalling. There can be several different potential causes of a lack of fuel flow. These can include broken or clogged injector(s), faulty or clogged fuel pump, clogged fuel filter, and broken fuel lines. Typically, if your car just has one bad injector it can still run, so usually a single-failed injector is not enough for a car to stall. However, it can happen, so we included it. 

Bad Gas

Another potential cause of your engine stalling is bad or contaminated gas, or from the tank being dry. Bad or contaminated gas can cause the engine to run poorly and shut off, and it can also cause serious engine damage depending on the contamination, too. Additionally, sometimes fuel gauges are incorrect. It’s always possible even if your car says it has some gas the gauge might be wrong and you might be empty. 

Usually, a problem with the fuel system will trigger a check engine light (CEL). If you get a CEL right before your car dies and it comes back for the fuel system, it’s a good chance that was the culprit. Another way to tell if it’s the fuel system is to check for leaks and monitor gas mileage. On older and extreme high-mileage cars the fuel lines can become corroded and rot, leading to leaking. If you start to notice extremely poor fuel economy, that might also be an indication of a fuel system problem. 

Cause #3 for Why A Vehicle Stalls – Sensor and Electrical Issues

For our third potential cause of a car stalling we are looking at sensor issues. As car manufacturers have modernized and made cars more efficient, they have also added literally hundreds of electrical parts and sensors. Most of these parts communicate with the ECU so the engine can run correctly, and the ECU has to take feedback from dozens of sensors at a time. 

Unfortunately, sensors are notorious for going bad. And since there are so many, it can be difficult to pinpoint exactly which is the problem. Some of the most common sensor failures that will cause a car to stall and die are the Manifold Absolute Pressure (MAP) Sensor, Mass AirFlow (MAF) Sensor, Throttle Position Sensor (TPS), and the camshaft and crankshaft position sensors. Any of these sensors can fail and cause the engine to stall out and become undrivable. 

Additionally, if you have electrical shorts, they can cause the engine to struggle to run. A bad connection with the battery can also result in power drivability and potentially even stalling out. 

Like the fuel system, usually if a sensor is reporting back abnormal or faulty information, your ECU will flag it and throw a CEL to alert you. For the most part, sensors are not too bad to replace, and often the most difficult part is finding access to the sensor in the first place.

Cause #4 for An Engine Stalling – Airflow Issues

As our penultimate cause of engine stalling, we’re looking at the final of our spark, fuel, and air trifecta: airflow. It’s pretty obvious, but just like fuel your engine cannot run without proper airflow. Air reaches your engine through the intake system, but luckily it’s not nearly as complicated as the fuel system.

Your engine’s intake system is primarily made up of the air box and air filter, intake tubing, throttle body, intake manifold, and cylinder head(s). Some cars also have forced induction in the form of a supercharger or turbocharger(s), and older vehicles use carburetors. Like the fuel system, if there is one broken link in the chain your engine will struggle to take in enough air and won’t be able to run. 

The most common problems with the intake system are air leaks, clogged or dirty air filter, broken throttle body, cracked intake manifold, or a broken air filter or air box. Usually, these items are pretty easy to spot. Or in the case of a broken throttle body, they will throw a CEL pretty quickly. Additionally, if you have a supercharger or turbocharger(s), the blower(s) might be bad and impede airflow. 

Another possible cause of poor airflow is bad air quality outside of the vehicle. Your car can only run on air immediately surrounding it. So if you are in an area with extreme smog or near a wildfire where the oxygen content is lower than normal, your engine might not have enough oxygen to properly operate, causing it to stall. 

For the most part, a broken intake is pretty rare and not nearly as common as a problem with the alternator, fueling system, or various sensors. However, it can happen, so make sure you don’t dismiss it before taking a look.

Cause #5 for Why An Engine Stalls – Timing Chain/Belt

For our final cause of why an engine stalls we’re looking at the timing chain or timing belt. Pretty much all modern engines have a timing chain or a timing belt. Their job is to synchronize the rotation of the crankshaft with the opening and closing of the valves through the camshaft(s). Your car has other belts too, like the drive belt or accessory belt. However, usually the timing belt will be the culprit if a car is stalling. 

Due to being cheap, many OEMs use less than optimal materials for timing chains. Many timing chains are plastic or polymer, and are very susceptible to failure. However, the trade-off vs a timing belt is that typically timing chains are not wear items and last the length of the motor. 

On the other hand, timing belts have to be replaced every 60,000-100,000 miles. If they are not replaced they are prone to snapping and breaking, which can have big problems. 

If your chain/belt breaks it can cause your engine to jump timing, which will interfere with the synchronization of the valves opening and closing and the engine firing. Additionally, if you have an interference engine, a broken timing chain or belt can lead to bent valves, necessitating the replacement of the entire valve train. 

Like the intake system, a broken timing chain or belt is lower on the list than the alternator and fuel system, but is still a possibility. Usually, the engine will run extremely poorly if it breaks the timing chain or belt, and it might fail to restart. You will likely get a host of CELs, your valves will make a ton of noise opening and closing, and you can visually inspect the belt/chain to see if it is broken or not.

How to Diagnose a Car Engine Stalling

Now that we’ve talked about the most common causes of an engine stalling, let’s look at how to diagnose them. We went over a few methods above, but this is a more broad look at how to diagnose many common problems. If you can’t find the issue using the methods above and below, you’ll probably have to consult a professional mechanic. Yet, if you can fix the problem yourself, you might potentially save hundreds in shop labor. 

How to Diagnose a Car Engine Stalling – Use a Code Reader

By far, the best tool you can use to diagnose a problem with your car stalling is a diagnostic trouble code (DTC) reader. These handy devices plug directly into the OBD-II port under your vehicle’s steering column. They are able to scan your car’s ECU to determine if any DTC or CEL codes are present and what they are. 

On most modern vehicles, if your engine senses a problem it’ll throw a CEL with a DTC. Typically, these codes narrow down the problem to a specific sensor or part, and tell you exactly what needs to be inspected or changed. It’s not always that easy, as sometimes multiple items can throw the same code, but it’s a great place to start looking for any problems. 

How to Diagnose a Car Engine Stalling – Consider All of the Vehicle’s Symptoms

In addition to using a DTC reader, you need to make sure you are taking all of the vehicle’s symptoms into account. Besides the engine stalling, what other problems are going on? Does the engine restart after stalling immediately, or do you have to wait a few hours before it’ll turn over again. Is your engine cranking but not starting after stalling, or not cranking at all? Do your lights turn on or is the car completely dead in the water?

Depending on what other symptoms there are, you can head in the right direction, or at least rule out a few things. If the car has zero power, not even for the locks, you might look at something simple like a disconnected battery, or something more tedious like an electrical short. Is the engine cranking but not starting? You’re probably looking at a spark or fuel problem. Does your engine refuse to start for a few hours after turning it off? Check your DTC reader for any crankshaft or camshaft position sensor codes right away. 

When diagnosing your car it’s important to be thorough or else you might just miss something obvious and waste a lot of time chasing a phantom problem with an easy solution. If you’ve gone through everything and still can’t diagnose the issue, it might just be best to hand things over to a qualified mechanic to get a professional opinion. 

How to Diagnose & Fix a Car Engine Stalling Summary

Dealing with a car stalling is one of the most frustrating issues one can experience. Typically, if your engine has stalled and is struggling to run, there is a problem with either the airflow, spark, or fuel. Engines need all three to successfully start and run, and if any one of the three is compromised so is the entire system. 

The most common causes for a car stalling include a bad alternator, faulty fuel system, faulty sensor, an electrical short, bad battery, compromised intake system, or a timing chain/belt issue. These are not the only potential causes of an engine not starting, but they are some of the most common. If you have a problem with your car stalling, these are the best places to start your diagnosis. 

How to Diagnose & Fix a Car Engine Stalling FAQ