Car Turns Off While Driving but Turns Back On (11 Reasons)

A car turning off while driving but restarting after (a.k.a stop-start) can signify several problems — most of which are related to that vehicle’s fuel, ignition, and air intake systems. In this article, we will discuss this incident in further detail and answer the question, “Why did my car turn off while driving?”

Factors like out-of-spec pressure levels, disrupted AFR, defective sensors, and a failing charging system can cause a car to turn off while driving but turn back on. Damaged serpentine belts and camshaft sensors are probable suspects, although there is little chance the affected car can restart.

Here are the top reasons a car turns off while driving but turns back on:

1. Empty Fuel Tank
2. Cracked or Damaged Torque Converter
3. Plugged Fuel Filters
4. Compromised Fuel Pump and Injectors
5. Timing Belt Failure
6. Malfunctioning Mass Airflow Sensor
7. Faulty Crankshaft Position Sensor
8. Defective Idle Air/Speed Control Actuator/Valve
9. Misfiring Ignition
10. Failing Alternator
11. Broken Engine Control Unit

Because multiple systems are involved, a car turning off while driving can leave owners confused and not knowing where to start. But worry no more, as I intend to shed light on the subject. Plus, I will throw in some tips to help deal with this unusual car behavior.

Top Reasons Car Turns Off While Driving

1. Empty Fuel Tank

One of the most obvious reasons behind a car turned off while driving is an empty tank. Now, you may think it silly for anyone to miss out on this. But it does happen (even to the best of us), mainly because of honest neglect or a faulty fuel gauge.

The first reason is self-explanatory, whereas the second one is often due to a sending unit failure. In this situation, constant wiper movement in the variable resistor wears down the resistive material strip inside the fuel gauge, causing it to get stuck in one position.

2. Cracked or Damaged Torque Converter

If you are still wondering, “Why did my car turn off while driving?” it may have something to do with a broken torque converter. This power transmission problem is unique to auto-transmission vehicles, as cars with manual gearboxes have a clutch to do the job.

Don’t get me wrong — torque converters are inherently durable. However, the component is only as tough as its weakest element.

A torque converter is a fluid coupler by design. It relies heavily on transmission fluid to operate correctly. Expectedly, the quality and state of transmission fluid used directly affect the whole (and smaller bits) of this component.

That said, it is ill-advised to use sub-par or contaminated fluid variants, as the latter is sure to wreak havoc on the converter and other transmission parts.

Fluids aside, other factors that can compromise a torque converter include deteriorating stator bushings and sealing rings, worn valve bodies and pumps, locked-up piston linings, and separated or dislodged turbine fins.

A torque converter (view on Amazon) getting warped or cracked is the rarest of these and is often traced back to improper transmission removal during servicing.

3. Plugged Fuel Filters

Another ‘contamination’ scenario that causes a vehicle to turn off while driving and restart after involves fuel system components — specifically fuel filters plugged due to old gasoline or petrol.

When fuel gets old or stale, it becomes gummy (due to olefins) or mucky (due to contaminants), blocking the filters. This outcome, in turn, prevents the fuel pump from pumping enough fuel for the engine, leading to restricted power output when driving at low speeds.

4. Compromised Fuel Pump and Injectors

Still on fuel system components, these two are also culprits to power loss while driving. Fuel pumps (view on Amazon) must be damage-free and in good condition to pump sufficient fuel and maintain fuel pressure according to spec. As for fuel injectors, they need to be clog-free to do a consistent spray of oil, lest stalling will occur.

A noteworthy fact about fuel injectors is that they get clogged more quickly than fuel filters, given their small orifice and carbon buildup that naturally results from the combustion process.

So when a car turns off when stopped at a light, it often means that scheduled maintenance and periodic cleaning are not happening as frequently as they should with the vehicle in question.

5. Timing Belt Failure

A damaged or slipping timing belt often results from the excessive load on a vehicle. However, it can also be attributed to misalignment, ratcheting (under-tension), worn pulleys, or a weak drive structure (often with high mileage or secondhand four-wheelers).

Whichever the trigger, a failing timing belt eventually renders camshafts inoperable and causes your engine to stop abruptly while on the road. This is a scenario most drivers would never want to find themselves in, as it often precedes severe engine damage.

6. Malfunctioning Mass Airflow Sensor

When it comes to engine-powered vehicles, achieving the right air-fuel ratio or AFR (which is 14.7:1 in most cases) is crucial to optimal performance.

This is where MAF sensors (view on Amazon) enter the picture. Tasked with measuring the air mass flowing into the engine intake, these sensors supply the ECU with vital information that the latter then uses to balance the air-fuel mixture.

As such, it is fundamental for modes of transport with controller modules to have well-functioning MAF sensors. Not only do they screen the quality and quantity of air entering the engine, but these sensors also determine the correct amount of oil the ECU needs to send to the power mill.

Conversely, defective MAF sensors give out incorrect readings, resulting in a car that turns off while driving but turns back on.

7. Faulty Crankshaft Position Sensor

Most modern vehicles have sensors for pretty much everything. According to Acko Drive, a standard sedan would have at least 14 sensors serving vital functions in different car systems. Of the list, the item above and the crankshaft position (CKP) sensor are some of the most important.

Interchangeable with the ‘engine speed sensor’ in Volkswagen models, a CKP sensor monitors the spinning speed and position of moving engine parts (engine valves, pistons, and crankshaft included).

Tracking these moving parts enable the optimal timing for ignition and fuel injection. Without accurate data on piston positioning from this sensor to the ECU, cylinders are more likely to misfire — resulting in instances where a car will turn off while driving but turn back on.

Signs such as an illuminated Check Engine Light, malfunctioning tachometer, or reduced fuel efficiency could signify something wrong with your crankshaft position sensor. However, note that these symptoms are not exclusive to the issue and would warrant a further diagnosis.

8. Defective Idle Air/Speed Control Actuator/Valve

Power loss does not only make a car turn off while driving but also during idling. And when this happens, you should inspect your IAC or ISC actuator.

Both actuators are functionally the same. The only difference is that the IAC actuator is used by fuel-injected cars, while the ISP actuator is utilized by carbureted vehicles.

As their names imply, these actuators control the engine’s idling rotational speed or RPMs and help keep it steady. Typically, idle RPMs range from 500 to 1,000 RPM in standard cars and 2,500 to 4,000 RPM in motorcycles.

Your owner’s manual may provide RPM figures different from those stated above. Regardless, watch out for erratic idle speeds and fluctuating RPM figures while your vehicle is in motion.

Several facets lead to a defective IAC or ISP actuator/valve. Upon inspection, you may discover that the valves are either deteriorating or obstructed or with a failing solenoid. Any of these impediments can cause your IAC/ISP valves to function poorly or be incapable of receiving electrical signals.

If uncertain, know that telltale signs such as starting issues, rough idling, and backfiring synchronous with inconsistent idle speeds are surefire indicators of a start-stop situation.

9. Misfiring Ignition

The combustion process (which is responsible for power output) will not be possible without one of these elements — air, fuel, and spark. And for the most part, the main culprits to a car turning off while driving have to do with the disrupted air-fuel ratio. However, we should not overlook the importance of spark, as it basically ignites air-fuel mixture.

Several things can go wrong with ignition. Any one of the following — a faulty ignition switch, a bad ignition relay, faulty spark plugs, or looseness/corrosion in the wiring harness (to name a few) — can cause an unstable or complete loss of connection to the ignition circuit.

The moment connection to the said circuitry becomes compromised, the power mill ends up with inadequate power (losing the ability to stay functioning when driving speed is reduced).

In the case of defective or fouled spark plugs, one faulty plug is enough to cause a start-stop situation. Suppose you discover more than one malfunctioning spark plug. In that case, you will likely experience engine stalling and abrupt shut-offs more often, with fewer chances of your vehicle restarting after it dies.

10. Failing Alternator

Another electrical component crucial to your car’s smooth operation is the alternator. It converts mechanical energy to a constant stream of electricity your four-wheeler needs to power electricals and accessories.

Given its nature, the alternator has a tremendous effect on spark ignition and other relevant processes (as well as your vehicle’s ability to go the distance).

Sure, your battery can supplement the function of your alternator (should it break down). However, it cannot do so for extended periods. Moreover, your battery’s ability to carry on with the alternator’s job makes it challenging to realize that the alternator (view on Amazon) is sometimes flawed.

If you pay close attention to your car’s body language, you may pick up on hints that your alternator is about to go out. Some early signs include a flashing dash, intermittent power output, and your A/C behaving erratically.

Check out this article that compares bad alternator vs. bad battery symptoms should you need help determining which of the two is the culprit.

11. Broken Engine Control Unit

Sometimes referred to as an engine management system, an ECU is an electronic device that serves as the engine’s brain. It is similar to an onboard computer, though smaller in scope and primarily focused on the inner workings of a vehicle’s engine.

Folks who still drive carbureted four-wheelers need not be bothered by it since they probably would not have one. However, everyone else outside this description should be concerned.

Since the ECU monitors and controls all internal combustion engine processes, keeping it in good working condition is essential — lest you risk a start-stop episode.

The most prevalent causes of a start-stop are generally horseshoed into the following categories — mechanical or physical, air-fuel related, and electrical.

Triggers emanating from a vehicle’s fuel system are the best-known of the lot, followed by issues with wiring and ignition. Mechanical or physical damage is the least likely to occur but is often the most costly.

Car Turning Off While Driving — Next Steps

Understanding the reasons above will help you pinpoint why your car turns off while driving. However, diagnosing the problem does not come into play until you have reached an auto repair shop or the safety of your garage. Therefore, I highly recommend doing the below steps at the first sign of a start-stop situation:

Pull Over to Safety

Because a start-stop episode is more likely to happen while you are on the road, the first thing to do is pull over to the nearest emergency lane or pump station (whichever is closer). Never attempt to brave the situation until you get home, as driving without braking or steering capabilities is extremely dangerous.

To add, a car turning off while driving is very uncharacteristic of a well-functioning vehicle (and a safe one at that!).

Turn on Hazard Lights

These emergency flashers should alert incoming traffic of your dilemma, allowing them to slow down or drive away from you on a highway.

Some online publications recommend this move when your car is completely immobile. However, it makes sense to do it even when your vehicle restarts.

Limit Yourself to Two Restarts

You would not necessarily find this in forums or publications. However, I strongly suggest heeding this rule.

When your car turns off while driving but turns back on, you do not necessarily know what is causing the hiccup. If it happens to be a bad alternator or battery, incessant restarts will only stress these components.

Call For Help or Roadside Assistance

If your vehicle completely dies on you, do not hesitate to call family, friends, or towing services. It would not hurt to ask for help. After all, no one wants to be stranded in the middle of nowhere and miles away from home.

Conclusion — Car Turns Off While Driving but Turns Back On

In summary, here are 11 of the most common reasons behind a car turning off while driving but turning back on:

1. Empty Fuel Tank
2. Cracked or Damaged Torque Converter
3. Plugged Fuel Filters
4. Compromised Fuel Pump and Injectors
5. Timing Belt Failure
6. Malfunctioning Mass Airflow Sensor
7. Faulty Crankshaft Position Sensor
8. Defective Idle Air/Speed Control Actuator/Valve
9. Misfiring Ignition
10. Failing Alternator
11. Broken Engine Control Unit

As established in this guide, there are multiple reasons for engines to fail to maintain power at low speeds. While many have to do with the three main car systems — fuel, air intake, and ignition — others stem from poor vehicle upkeep, physical damage to components, or simply natural wear and tear.

So the next time your vehicle decides to act up (though I hope not), keep calm and prioritize pulling over to safety. Follow that up with a thorough inspection and careful diagnosis of suspected systems and components.

Most importantly, do not blame yourself. Know that no matter how well you care for your four-wheeler, its overall performance will deteriorate over time.