A vehicle that suddenly shuts off when you stop isn’t just a nuisance. It’s also a big red flag that you should never ignore. In most cases, it’s a sign that there’s something wrong with your car, so it’s important to figure out what’s causing your engine to turn off or stall before it gets worse.
Here are the possible reasons why your car suddenly turns off when stopped:
The idle air control (IAC) valve regulates airflow when the throttle is closed, allowing your engine to idle smoothly. When an IAC valve malfunctions, it can restrict the airflow and cause the engine to turn off when you stop your car.
A dirty or clogged fuel injector won’t be able to deliver sufficient fuel to the engine. This can cause the engine to stall or perform poorly when idling or accelerating.
If your car shuts off when stopped or slowing down, a faulty fuel pump might be to blame. A bad fuel pump won’t be able to pump gas from the tank to the engine, causing your car to jerk or stall.
An overheating engine can trigger various safety features to prevent further damage to the vehicle. For some vehicles, this can include the engine automatically turning off.
If your car stalls when braking, then the issue might be your alternator. The alternator powers your vehicle’s electrical systems, so if it fails, the engine is likely to stall when you stop. A malfunctioning alternator can also cause your battery to die and your lights to dim or flicker.
As your vehicle’s main computer, the powertrain control module (PCM) can cause several issues when it malfunctions. This includes an illuminated check engine light, poor fuel economy, and increased emissions. It can also cause your vehicle to shut off when coming to a complete stop.
A crack or loose vacuum hose can allow air to enter or escape the engine, interfering with the air-fuel mixture. This can significantly affect the engine’s performance, such as a complete shutdown when accelerating, slowing down, or coming to a stop.
Most spark plugs last around 80,000 miles until they start to show signs of wear, such as misfires, poor engine performance, and even stalling. Depending on how worn-out they are, spark plugs can cause your vehicle to stall at various revolutions per minute (RPM).
Clogged air or fuel filters can restrict air or gas flow to the engine, resulting in a rich or lean air-fuel ratio. When left unchecked, this can eventually cause your engine to idle roughly, struggle to start, or just shut down.
Diagnosing a car that suddenly shuts off when you slow down can be tricky, especially because the issues mentioned above can also cause it. Here are other possible causes to consider:
Soot, carbon deposits, and other contaminants can build up and cause the exhaust gas recirculation (EGR) valve to stay open. When this happens, exhaust gases continuously flow into the intake manifold. This can disrupt the engine’s air-fuel mixture and cause stalling.
When a damaged torque converter fails to disengage when you decelerate, the excess power from the engine can cause it to stall or idle roughly. In some cases, it can also cause the transmission to slip.
Your vehicle relies on several different sensors to ensure the engine and various systems are all functioning properly. If any of these sensors malfunction, then your car can suddenly shut off on its own.
For example, a faulty oxygen (O2) sensor can send inaccurate data to the PCM, causing the PCM to unnecessarily adjust the airflow. This can lead to a lean or rich air-fuel ratio, which can cause your car to shut off.
Electrical issues, such as a faulty ignition switch, damaged wirings, and malfunctioning electronic control units (ECUs), can cause your engine to stall, backfire, or perform poorly.
Most modern vehicles come with a start-stop system, which temporarily shuts off the engine when you step on the brakes. While the exact technology can differ depending on your vehicle’s year, make, and model, this is how most start-stop systems work:
It’s a convenient feature that lessens emissions and fuel consumption.
With so many possible causes behind a stalling vehicle, repairs can certainly be a headache. Luckily, prevention is quite simple. Here are helpful tips on how to prevent your car from stalling:
A scan tool can also come in handy when spotting any issues early, so consider investing in one of your own.
Any information provided on this Website is for informational purposes only and is not intended to replace consultation with a professional mechanic. The accuracy and timeliness of the information may change from the time of publication.