What causes a loss of power in a car?

What causes a loss of power in a car?
Suffering power loss in your car can be a frustrating experience and indicate a problem with your vehicle’s engine.

If your car is losing power, it is important that you know how to respond in order to stay safe and prevent any potential damage to your vehicle.

Hopefully you won't experience power loss with your vehicle, but in case you do, ensure you have RAC Breakdown Cover.

RAC Mobile Mechanics also offer repair and diagnostic services, which will identify the cause of your car's loss of power and ensure it is repaired to the highest standard. 

This guide looks at all the potential causes for a loss of power in your car – and what you can do to fix it.

Loss of power in a car – common causes

Although losing power when driving can be a difficult situation for drivers of all ages and experience levels, it is important to stay calm and stop the car when it is safe to do so.

A loss of power will be most noticeable when you are trying to accelerate – however, it can also happen suddenly when maintaining a speed or intermintely (with the car losing power before it comes back again).

Reasons for loss of power in a car:

  1. Damaged or worn-out spark plugs
  2. Clogged DPF (diesel particulate filter)
  3. Blocked air filters
  4. Engine Control Unit (ECU) errors
  5. Backfiring exhaust
  6. Gear slipping
  7. Sensor malfunction
  8. Broken fuel injector(s)
  9. Issues with catalytic converter
  10. Air conditioner draining power in hot temperatures
  11. Underperforming turbocharger
  12. General wear and tear

Although these are the main reasons, there could also be a wider issue with the vehicle that will need to be addressed at a local garage or by a mobile mechanic.

How to fix loss of power in a car

There are many reasons why your vehicle may lose power – here is what to look out for and what to do next.

Spark plugs

Over time, spark plugs can lose their effectiveness in powering the engine – and will either need to be repaired or replaced.

You will notice that there will also be a rattling sound and soon you will not be able to start the engine.

DPF filter

A Diesel Particulate Filter (DPF) is designed to remove matter and exhaust pollutant particles when driving.

However, over a period of time they can become blocked – forcing your vehicle to enter ‘limp-home mode’. This is where your vehicle will have very little power output.

It stops further damage to other parts of the vehicle.

You can avoid this issue by driving on the motorway at the speed limit for more than 30 minutes. This is known as passive regeneration and can help burn off excess soot in the filter.

Some vehicle’s use active regeneration where extra fuel is injected to raise the temperature in the filters.

If neither of these work, then you’ll need to visit your local garage and have a ‘forced regeneration’ of the DPF.

Air/fuel filters

Vehicles have their own air and fuel filters to help protect the quality of the air and fuel – and keep dirt particles out of the engine.

If the filters are worn or dirty, it can disrupt the air or fuel flow and result in a loss of power.  

In most cases, a filter replacement will be necessary to rectify the problem.


The Engine Control Unit (ECU) can sometimes give false readings which will cause the engine to lose power.

In other cases, it can cause the vehicle to come to a complete stop. This is because the ECU’s programming believes that there is a serious issue with the car.

Park somewhere safe, turn off the engine and let it cool down. Restart the engine and see if the same issue persists.

If so, you may need to contact a garage or local mechanic.

There are several other reasons why the ECU is having issues. Knowing what your car dashboard warning lights mean can be helpful.


If your exhaust is blocked or damaged then your vehicle will immediately lose power.

However, a backfiring exhaust happens when there is an incorrect ration of fuel to air within the vehicle. You will hear a loud pop or bang coming from the rear of the vehicle.

This is something that could lead to more serious damage to your car, so take your vehicle to a mechanic as soon as possible.

Gears and clutch

If your gears are slipping, then it will lead to the vehicle’s power being impacted.

This is because the engine's output fails to reach the wheels effectively.

Clutch or gear slipping should be dealt with by a local garage that can get a greater understanding of why it has happened and what to do next. 


In modern vehicles, there are many sensors for different purposes.

If there is an issue with them or the information that they are feeding back to the ECU is incorrect, it could lead to the vehicle having less power.

This is typical with a Mass Air Flow (MAF) sensor, which monitors the air intake to the throttle when accelerating.

Fuel injectors

When an engine is turned on, the fuel injectors send fuel into the combustion engine.

If there is a lack of pressure, then an incorrect amount of fuel will be added – creating a lack of power.

Worryingly, it will also lead to other issues in the engine that can be very costly.

This is a technical job and should only be carried out by a qualified mechanic.

Catalytic converter

Responsible for controlling the emissions that leave the car’s exhaust system, a catalytic converter can become clogged over time, leading to a lack of power and acceleration.

They are popular for thieves, so protect your catalytic converter today.

The first sign there is a blockage is a lack of power – however, if the issue isn’t resolved quickly then it can lead to a total engine failure.

Air conditioner

Although this is more common in older vehicles, on a hot summer day, you may be using the air conditioner. However, if it isn’t in top working order, then it can start draining power from other parts of the vehicle.

A re-gas might help with this – but it might just be a side effect of a day with high temperatures.


Once only found in sports cars, turbochargers are now a common sight in modern vehicles due to the performance and fuel economy benefits they provide.

The turbocharger works by increasing the air pressure in a combustion engine, which allows more fuel to be added into the mix. This then creates extra power when accelerating.

However, when they have a problem, they work in the opposite way and cause a drag on power. This can range from having dirt and debris in the turbocharger, to a loose connection, to having major damage to the unit or the connectors.

They also need to have the right oil and filters attached to work properly.

As there are more specialised in how they work and they are worked on, it is advisable to take your car to a mechanic to get any issues with your turbocharger fixed.

Wear and tear

Like many other parts of a vehicle, over time and many trips on the road, parts of the engine can wear down – which can sometimes lead to problems.

Regular car servicing will help with this, along with any suggestions at the annual MOT.

If you have any questions about loss if power in your vehicle, then please leave them in the comments section below.

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