Car Dies While Driving But Restarts [I fixed after cleaning throttle body]

If your car dies while driving but restarts after a while, there are many reasons that could have caused it. Some of those reasons may be mechanical, and some may be electrical. Maybe you’ve got a broken part or bad wiring. There are many things that can go wrong in the powertrain of your car, and many of them can be fixed. In this guide, I’ll discuss some most common reasons that cause your car to turn off while driving.

If your car dies while driving but restarts, there can be problems with the battery, starter, serpentine belt, electrical wiring harness, ignition switch, alternator, throttle body, MAF sensor, crankshaft position sensor, ignition coil module, and fuel delivery system.

If your car won’t start after replacing the crankshaft position sensor, you should read this guide.

If your car dies while driving, you should use OBD2 scan tool to pull out all trouble codes stored in the engine’s memory to find the root cause of your car turning on and off randomly while driving.

Bonus Read: My car starts sometimes and sometimes it doesn’t

Causes Of Car Dying While Driving

Here are some of the most common causes of car dying while driving.

1. Failed Car Battery To Provide Power

The most common reason for a car dying while driving is a failed car battery. 

Car batteries are the heart of your vehicle. If your car battery is old, it may not be able to provide adequate power to start your engine. This could result in your car not starting at all, or the engine starting but then failing to keep going. 

A healthy battery has a voltage of:

  • 12.6V when fully charged and the engine is not running
  • 13.5 to 14.5V when the engine is running
  • 9.6 to 10V when the engine just cranks before starting (it only drops to 9.6V for a couple of seconds when the engine cranks). As the engine starts running, the alternator supplies the current to the battery.

You should check the voltage of your car’s battery using a voltmeter in those conditions. You should connect the red probe of the voltmeter with the positive terminal of the battery and the black probe with the negative terminal. If the voltage of the battery is less than 13.5V when the engine is running, it means that either the car’s battery is faulty or the alternator is not charging the battery.

2. Loose Battery Terminals

Loose battery terminals are one of the most common causes of car breakdowns. If your car turns off while driving, it’s likely that the battery terminals are to blame. The battery terminals are the metal posts that connect the battery to the car’s electrical system. Over time, they can become corroded or loose, which can cause all sorts of problems. 

If the battery terminals are loose, it can cause the battery to lose power and the car to turn off. This is because the electrical current can’t flow freely between the battery and the electrical connections of the car. 

In my guide on car won’t start after changing battery, you can learn more about loose battery terminals.

3. A Bad Alternator Is Not Charging The Battery

The alternator is just like a generator that produces an electric current to charge your car’s battery while the engine is running. The alternator runs from the power of the engine that is supplied through the serpentine belt (also called an auxiliary belt). The serpentine belt runs over the crankshaft pulley, which then supplies power to the pulley connected to the alternator.

serpentine belt of an engine

The purpose of an alternator is to keep your battery charged and supply power to the auxiliaries of the engine while the engine is running. If the alternator is bad, the battery will die, and the car will turn off while driving.

If the voltage of a battery is less than 13.5V while the engine is running, it means that the alternator is either faulty or the serpentine belt is damaged.

The symptoms of a bad alternator that is not charging the battery include:

  1. Alternator is overheated and begins to smell. You should check the settings of voltage regulator. If the voltage setting is below 13.5V, it will cause overheating of the alternator due to a large amount of current flowing through it.
  2. Charging lamp (battery light) will light on the dashboard
  3. Charging lamp does not turn off after start. When the engine is started, the charging lamp turns on for a couple of seconds to indicate that the lamp is working fine. If it does not turn off after a few seconds of starting the car, it probably means there’s something wrong with the alternator.
  4. The alternator is flooded with oil. In that case, you should check the surroundings of the alternator, such as the filter and oil on the pumps.
  5. The fuse is blown.
  6. The cable or plug of the alternator is rusty.

4. Damaged Serpentine Belt

The serpentine belt transfers the mechanical energy of the engine from the crankshaft to auxiliaries of the engine like the water pump, AC compressor, and alternator.

When the serpentine belt breaks, the alternator will not produce electrical energy and stop charging the battery.

If the serpentine belt is damaged, you will hear unusual noises clicking noises from the engine. Moreover, if the serpentine belt has slack, it will not be able to supply power efficiently from the engine to the alternator.

Furthermore, the serpentine belt has both a tensioner and an idler pulley. There is a chance that the pulley of the serpentine belt does not turn smoothly and there is a play from side to side that can prevent the serpentine belt from stretching. 

Check out the below video to learn about the failure models of the serpentine belt.

5. Damaged Electrical Connections To The Ground and Starter

When there’s a problem with the electrical connections of your car, that current can’t flow properly and your car will shut down. There are a few different things that can cause electrical problems like this. It could be a loose connection, a corroded connector, a short circuit, or a break in the wire. Whatever the cause, it’s important to get it fixed as soon as possible because driving with a damaged electrical system can be very dangerous. 

In your engine, the negative terminal of the battery is grounded to the engine block, chassis, and other metal parts. So, you have to visually inspect those ground connections of your vehicle.

To test the ground connections of your car, take a voltmeter. Connect one probe with the negative terminal of the battery and the other on the engine block or chassis. If the connections are fine, there will be 0v recorded on the voltmeter when trying to start an engine. If you can see any voltage, it means battery ground connections are damaged.

In some engines, there is also a ground strap connection between the car body and the engine. Its ends are usually mounted on the transmission and car body. If the ground strap is weak or torn in any way, it could also car not to start.

Now, repeat the test by connecting a probe voltmeter with the positive terminal of the battery and another probe with the solenoid terminal of the starter. Ideally, there should be no voltage drop across the battery-positive terminal and starter solenoid terminal (also called S terminal) i.e. there should be negligible resistance in the circuit. So, if the connections are good, the voltmeter will show a voltage of less than 0.2V.

6. Bad Throttle Body

The throttle body of an engine regulates the amount of air to enter the engine’s cylinder based on the position of the accelerator pedal. It has a butterfly valve that is mechanically or electronically controlled, depending on the engine. 

The mechanical throttle body is driven by a throttle cable that links the accelerator pedal to the throttle plate. If the throttle cable is too tight or sticking a little, it will not be able to have full control over the throttle plate. As a result, your car engine’s RPM will boggle without pushing a gas pedal.

The electronic throttle body is controlled by the ECU. The accelerator pedal sensor sends signals to the ECU so that it can compute how much the throttle valve should be opened.

When the throttle body is not working properly, it can cause the car to stall and eventually die out while driving. This can happen for a number of reasons, but the most common cause is a build-up of carbon deposits on the throttle body. Over time, these carbon deposits can build up and restrict the airflow to the engine, causing the car to lose power and eventually die out. 

Also, carbon deposits in the throttle body prevent the butterfly valve to rotate freely under the action of a spring.

In the electronic throttle body, you will see a port where a harness connector is plugged into the throttle body. In that case, you have to test voltage signals at the harness connector of the throttle body and the resistance between the terminals of the throttle body actuator. In my guide on P1516 code I have explained the process of testing the throttle body. 

If the throttle body passes electrical tests, you should check for any carbon deposits inside the throttle body. You can use this throttle body cleaner to clean the throttle body. Make sure that the throttle plate of a throttle body is not binding when you try to move it with your finger. i

The butterfly valve of the throttle body should rotate freely under the action of a spring force. Moreover, you have to perform the ECU relearn procedure for an electronic throttle body after cleaning. I have explained the procedure of throttle body relearn in my guide on the P1516 code I linked above.

7. Bad MAF Sensor

If the MAF sensor is not working properly, it can cause the car to die out while driving. This is because the MAF sensor is responsible for measuring the amount of air that enters the engine. If the MAF sensor is not working properly, it will not be able to measure the amount of air correctly, and the engine will not be able to run properly.

For proper combustion and smooth engine operation, a correct air-fuel mixture ratio is needed. If the MAF sensor does not correctly measure the amount of air entering the engine, the ECU couldn’t measure the desired amount of fuel to be injected into the combustion chamber. As a result, it will also cause your car to die out while driving.

Note: Keep in mind that older engines have a Manifold Pressure (MAP) sensor instead of a MAF sensor. So, it depends on which engine you have. The MAP sensor cannot be cleaned. So, you have to replace it.

To clean the MAF sensor, follow these steps:

  • Disconnect the negative terminal of the battery.
    Remove the MAF sensor, it is located on the intake tube between the air filter box and the throttle body of the engine.
  • Spray all of the little sensors you see inside of the MAF carefully with this MAF sensor cleaner. Avoid touching the wires of the MAF sensor. It will damage it.
  • Reinstall and reconnect the battery terminal.
  • Start the engine and let the ECU relearn idle for 15 minutes.

I found the following Youtube video helpful for cleaning the MAF sensor:

Before testing the MAF sensor, you also have to visually inspect and test the harness connector of the MAF sensor for any intermittent electric connection. If the car restarts again after turning off, it usually indicates intermittent electric faults in the circuit.

You can watch the below video for a better understanding of the testing of the MAF sensor:

8. Bad Fuel Injector

A fuel injector is responsible for delivering fuel to the engine. If it’s not working properly, the engine can’t run. 

There are a few signs that your fuel injector is going bad. If you notice any of these, it’s time to get it checked out.

  • Your car is hard to start – If your car takes a long time to start, or if it’s hard to start, it could be a sign of a bad fuel injector.
  • Your car is running rough – If your car is running rough, it’s another sign that your fuel injector is going bad. The engine may misfire, or it may run unevenly.
  • Your car is stalling – If your car stalls, it’s a sure sign that something is wrong with your fuel injector.
  • Your car is getting poor gas mileage – If you’re noticing that your car is getting poor gas mileage, it could be because of a bad fuel injector.
  • Your check engine light is on – If your check engine light is on, it’s a good idea to get your car checked out. It could be a sign of a bad fuel injector.

If the fuel if the injector is dirty or clogged, it can restrict the flow of fuel to the engine, causing the engine to stall and die out eventually. Moreover, if the fuel injector is faulty, it may not be able to properly control the flow of fuel to the engine, causing the engine to die out. You can read my guide on car won’t start after changing the fuel injector to learn how fuel injectors become bad.

9. Clogged Fuel Filter

The fuel filter is responsible for keeping the fuel in your car clean. Over time, it can become clogged with dirt and debris. When this happens, the fuel can’t flow through the filter properly. This can cause the engine to stall or even turn off. An engine can have multiple fuel filters. So, you should check out how many fuel filters your engine has. It is recommended to change the fuel filter after 30,000 miles or every 12 months.

10. Bad Ignition Coils

Ignition coils in an engine are responsible to convert a 12V from the battery into thousands of volts to generate a spark from a spark plug. If the ignition coil is getting an intermittent supply of current, your car may die out while driving and then restart again.

The configuration of ignition coils depends on the engine. Modern engines have an ignition coil on each spark plug (also called COP configuration). Older engines have only one ignition coil that supplies voltage to all spark plugs through the distributor cap. In that case, you have to check for carbon and oil deposits inside the distributor cap.

Furthermore, the contacts on the cap and rotor wear down over time due to high voltages and crossfire.

11. Faulty Ignition Switch

A faulty ignition switch also causes your car to die out while driving. The ignition switch is responsible for turning the key on and off. When the key is turned on, the electrical current passes through the ignition switch, which then sends the signal to the starter motor to turn the engine on.

The ignition switch is located behind the ignition lock and is made up of many small metal plates. Over time, these plates can build up rust and one may lose connection. This can cause the engine to shut off abruptly. Another possibility is that the ignition relay has gone bad and is no longer able to control the amount of electricity going through it.

12. Bad Cam Phaser

Cam phasers are used in variable valve timing engines to adjust the opening and closing of the engine’s inlet and exhaust valves at higher speeds.

There are a few symptoms of a bad cam phaser, including:

  • The engine stalling
  • The engine is hard to start
  • The engine running rough
  • The engine misfiring
  • The check engine light is on

There are a number of reasons why your cam phaser may not be working properly. One possibility is that the cam phaser is dirty or damaged. Another possibility is that the phaser is not properly lubricated.