Top 10 reasons why your car is stalling

May 10, 2021
Top 10 reasons why your car is stalling

Why does my car keep on stalling or cutting out?

Have you ever been driving along to find your engine simply judders to a stop? or pull up at a junction/traffic lights to find your engine simply cuts out rather than idles as expected? It's one of the top fears for any driver to find an engine simply stop running! In this article we take a look at the most common causes of stalling.

What happens when your car stalls or cuts out?

Stalling is the terminology given when a running engine comes to a stop by itself. This can be a gradual stall which is similar to an engine being switched off or it can be a sudden jolt with the engine stalling. This is quite often accompanied by an array of warning lights on your dash.

An engine stall can happen at any time when driving or idling the engine. It is important to remember that when driving an engine stall will also cause limited brakes, loss of power steering and complete loss of engine power. If the engine doesn't restart you will also find it difficult to move the car on your own without power steering or engine power.

It is also possible to stall the car by not engaging neutral gear when stopping, selecting the wrong gear (e.g. pulling away in 3rd) or even braking whilst still in gear. This is known as a sudden or jolt stall and will instantly cut the engine, often in a loud dramatic way.

So may car has stalled, what should I do now?

The immediate reaction to a stall should be your safety. Put your hazard lights on to alert other road users, if you are still moving then attempt to get the vehicle into a safe space away from other traffic such as the side of the road.

Once you are stationary, ensure the car is in neutral and attempt to restart the car. Most of the time the car will restart and you can then carry on your journey and seek mechanical help as soon as practically possible. If the car doesn't start it is worth waiting for 30 seconds or so and attempting a restart.

If the car is still not starting then you need to exit the vehicle away from traffic (e.g. passenger door if parked on side of the road) and move away from the live traffic lanes (going over any barriers). Once in a safe location you can call for assistance from your breakdown company or a local garage (such as Whatlington Garage) who can advise & recover.

Can an Automatic car stall as well?

Simple answer, Yes! A stalling engine can be for many reasons, the transmission is only one of those. Even then, an automatic car uses a torque converter which can cause an engine stall on idle when it fails.

The common reasons for a stalling car

There are numerous reasons a car can stall whilst moving or attempting to idle. We have compiled the following list which covers the most common reasons (but obviously not all reasons!) which can cause a stall to occur. It is always strongly advised to get your car checked as quickly as possible after a stall to ensure that any problems are swiftly dealt with

1. Faulty Alternator / Battery

In order for your vehicle to carry on running it requires a consistent voltage to keep the electrical systems alive and active. This is managed by a device known as the alternator that converts spinning motion to electrical energy which keeps your battery topped up and charged whilst providing enough voltage for the electrics in your car to operate.

When the alternator becomes faulty, or if your battery is faulty and drops below voltage then you run the risk of any of the electrical systems in the car stopping. When the electrical system is unable to function you will find the car is unable to keep it's engine running and will promptly stall and bring itself to a halt.

The common issues we see with alternators are snapped or broken belts that spin the alternator, poorly tensioned belts, a failed alternator unit or a dead battery.

We supply and fit a range of Bosch batteries and can get your battery test for you too, just contact us.

2. Faulty Fuel System

The fuel system is fundamental to the engine running correctly, smoothly and efficiently. There can be numerous faults in the fuel system that can cause symptoms such as the car not starting, running lumpy or stalling whilst running. When part of the fuel system fails, or is beginning to fail, the mixture of air & fuel delivered to the engine becomes a different ratio to what the engine is expecting to receive and thus can cause a stall.

Common reasons for the fuel system to fail can be a number of issues including faulty/failing fuel pumps, blocked fuel filters, poor/blocked injectors, low fuel pressure, failed pressure regulators and even fuel leaks. You can also find poor fuel will also cause stalling from dirt/silt in the tank, ingress of water into the fuel, mixed fuel (e.g. diesel in a petrol or vice versa) and even poor quality or contaminated fuel from the station.

Modern engines are a complex engineering feat that require a precise mixture of air and fuel in order to run smoothly. When the system fails and this mixture is thrown out of balance a whole world of issues can occur which often result in poor running or even stalling of the engine.

3. Faulty EGR Valve

The Exhaust Gas Recirculation Valve, also known as the EGR valve is an important part of the emissions control system on many modern cars. This special valve allows exhaust gasses to recirculate back through the engine at higher temperatures by the way of a simple valve.

There are many reasons why an EGR valve may fail but by the nature of it being a mechanical valve controlled by an electronic motor they are prone to electrical faults or carbon build up causing the valve to stick open or shut.

Common systems on a failed valve will include poor performance, poor running, excess smoke or stalling engines. In regards to this blog post, an EGR valve stuck open will constantly allow exhaust gasses back into the engine when cold or idling and this can cause the car to run very roughly and thus result in stalling or even stopping the car from starting.

4. Faulty DPF Filter

DPF filters are a recent addition to help combat the emissions from a diesel vehicle. Known as a Diesel Particulate Filter, they are designed to catch and burn off the exhaust emission particles reducing the levels that leave the exhaust. The DPF is a common fail point for many motorists and can become bad either from a blocked filter or the electronics that manage the load and regeneration of the filter itself.

The most common issue is a DPF filter blocking up, normally caused by many short journeys which stop the filter getting hot enough to carry out what's known as a regeneration. When this happens the filter blocks causing back pressure and ultimately causing the vehicle to dramatically loose power (limp mode) and even stall or refuse to start. There are 3 options open to us for when this happens including forcing a regeneration, removing the DPF to clean it manually or replacing the filter. The DPF's are not designed to last the life time of the car and often have an age limit (like a clutch).

There are other reasons for a DPF fail. The system uses a setup of temperature sensors and pressure sensors combined with other specifics in order to monitor the soot/ash levels and control the DPF. If any of these sensors has a fault it can stop the DPF regenerating and cause it to block. Most car manufactures will also stop a DPF from regenerating if there are other electrical faults present on the vehicle so we always carry out a full diagnostic for any DPF issue.

Aside from the common symptoms of loss of power, stalling, smoke and limp mode you will also normally see other signs. You should also get a combination of lights on your dash too. Initially this is normally the DPF symbol and eventually will turn into the Engine Management Light (EML or MIL, often called the Emissions control light in user manuals) and lastly you may also see a flashing orange coil light too.

It is imperative to get a DPF issue look at as quickly as possibly, the longer you leave a DPF issue the more likely it is to be an expensive repair. Catching and cleaning or sorting an issue early can save time, money and breakdowns.

We can regenerate, clean and renew DPF filters, if you want to book or have some questions please contact us.

5. Clutch, Torque Converters & Gearbox Problems

The clutch controls the movement of power from your engine through to your gearbox via the means of a clutch plate. This is different to an automatic which generally uses a torque converter to put power through. In all instances a fault within these parts can cause either slipping or drag/seizing of components.

When a clutch slips, it means the friction material isn't gripping and the power isn't being transferred to the wheels. The more you accelerate or try to move the less progress you will make. Normally this is displayed as a revving engine with no vehicle movement and normally accompanied by a strong burning smell.

A clutch can also drag, stick on or seize and this often results in a vehicle stalling or the vehicle still moving despite the clutch pedal being all the way down. Lastly the gearbox can be prone to wear, tear and internal damage that ultimately can seize up and cause the engine to stall.

The majority of clutch problems will stop the car from driving and end up requiring recovery, however if you get the car checked on the first signs of clutch symptoms they can often be caught before it causes a stall or recovery situation.

We carry out many clutch replacements and help with gearbox rebuilds. Contact us for more information.

6. Coolant / Overheating

Most cars have a fairly simple cooling system but when this fails it can cause temperatures to climb sky high. With a rising temperature that is being monitored by the ECU a car will eventually stall and possibly even refuse to restart again.

There are many reasons for an overheating car, from a coolant leak meaning the engine is running without coolant to a broken water pump, blocked radiator or a stuck thermostat. We also see more severe problems such as blown head gaskets, damaged EGR coolers and damaged oil coolers. We always advise to get the water pump replaced at the same time as the timing belt to help prevent issues with broken or leaking pumps.

7. Alarm & Immobiliser

Virtually all modern vehicles are fitted with an alarm system and immobiliser as standard. Whilst these systems do a great job at reducing theft of vehicles, they also pose problems when they go wrong. When you first start your vehicle the car is looking for a recognised key which is then uses to turn off the alarm. If for any reason the car loses communication with the key, especially on contactless vehicles then the car will turn off. Quite often in this scenario the car will also refuse to restart unless it can redetect the key.

Common causes of this can be as simple as the battery in the key going low, or even forgetting to put the key inside the car! There are more serious issues which can occur such as the transponder chips, pickup rings, alarm ECU's, wiring etc all playing vital roles that are prone to failure.

8. Engine Timing

Probably the most important aspect of the engine is the timing between the bottom block and the cylinder head on the top. This is normally achieved by a Timing Belt that connects the two but can also be a timing chain. Various issues can occur which cause the two sections to come out of time and thus causing the engine to come to a (normally, catastrophic) stop!.

Whether the timing device (belt or chain) has snapped, or simply slipped, when the timing is incorrectly or completely missing the engine cannot run. Most engines are known as 'interference type' engines meaning when the timing fails it causes serious damage to the engine internals that often requires a full engine rebuild.

If you have a timing belt it is essential that the belt and tensioner/pulleys are changed on a regular basis according to the manufactures guidelines. If your engine has a chain then regular, strict oil changes and immediate investigation on any chain noise is essential. By keeping up with preventative maintenance you can avoid this costly 'engine stalling' scenario.

9. Electrical

All the time your engine is on and running the engine is constantly monitored by a range of sensors. The cars ECU will monitor all the sensors in real time and use the data provided to adjust air & fuel ratios. If for any reason there is a failure in this electrical network of sensors then the ECU get's or gives incorrect information that ultimately can lead to the engine stalling and not running.

It is common for many sensors to get 'lazy' with age or to have a working life which causes them to either stop working or read outside of their calibrated or known ranges. As well as this, we also see broken wires, broken connectors, water ingress and internal ECU faults.

There are of course other electrical issues which can cause issues too, such as the alternator not supplying power to keep the electrical system running, a poor/dead battery or even a failed earth connection. Lastly there are also fuses, relays and other sensitive circuits the car depends upon to start and run which can all fail for various reasons.

10. User Error

A car can stall simply by user error, it's nothing to be embarrassed about and happens from time to time with even the most advanced drivers, especially when driving a new or unfamiliar vehicle. Simply selecting the wrong gear, not giving enough acceleration when pulling away, applying the brakes without dipping the clutch etc can all cause your car to judder to a stop. The great news with this is there's nothing wrong with the car, so just restart and off you go.