Why Does My Car Lose Power?
FixMyCar explains why your car might be losing power and what you can do to fix it.
Book a car repair nowEllie Dyer-Brown
Monday August 11 2025
5 min read
Most drivers know their cars inside out, meaning they can tell immediately when the engine isn’t giving them as much power as it usually would. A loss of power will be most apparent during acceleration, but even when driving at a constant speed, you may notice your car flagging.
If this is the case, we know how eager you’ll be to fix the problem, so we’ve created this guide to help you diagnose what might be going wrong.
1. Clogged fuel filter
The fuel filter plays a vital role in ensuring that the correct quantity of fuel, free from dirt particles, reaches the engine chamber. Sometimes, the fuel filter becomes clogged with debris; when this happens, the engine can’t perform at its optimum level. When you put your foot down, more fuel will be sent to the filter, but not as much will be able to get through, resulting in a loss of power.
How much does it cost to fix a clogged fuel filter?
Replacing a fuel filter typically costs between £60-90.
2. Clogged catalytic converter
Catalytic converters control the emissions that leave your exhaust. They contain aluminium or ceramic honeycomb mesh coated with platinum and palladium, which chemically react with carbon monoxide and unburnt fuel. This redox reaction results in the creation of carbon dioxide and water, two much less harmful by-products.
Learn more about how catalytic converters work.
When catalytic converters become clogged, the first sign is usually a loss of power. Eventually, this can lead to engine failure if left untreated, so it’s best to book in with a local garage as soon as possible.
How much does it cost to fix a clogged catalytic converter?
The average price of a catalytic converter replacement on FixMyCar is £509.20.
3. Clogged air filter
Before air enters the combustion chamber, it must be filtered to make sure it's free from debris and impurities that might otherwise cause damage.
As you might expect, air filters tend to get clogged when used for a while, limiting the amount of air getting into the combustion chamber. Consequently, the engine struggles to generate enough power.
How much does it cost to fix a clogged air filter?
Getting your air filter replaced shouldn’t cost you too much - around £60 - and as soon as it’s done, your car will be back up to full power.
4. ECU error
Your car might lose power if the engine control unit (ECU) detects a mechanical error in the car that doesn’t exist. When this happens, the ECU might reduce the cars power, sending it into limp mode. In some cases, it might stop completely to prevent an accident.
ECU errors like this may go away on their own, but you should still take your car to be checked by a professional to make sure that it doesn’t happen again.
How much does it cost to fix an ECU error?
The average price of an ECU repair on FixMyCar is £170.87.
5. Faulty fuel injectors
Fuel injectors are responsible for introducing fuel into the combustion chamber. This process happens at extremely high pressure, and the amount of fuel must be precise for combustion to happen successfully. Even a slight miscalculation will disrupt the process, resulting in a loss of power. In the worst-case scenario, your cams and pistons may break, making the repair bill significantly more costly.
How much does it cost to fix faulty fuel injectors?
On average, a fuel injection system repair costs £244.86.
6. Worn spark plugs
If your car feels particularly unresponsive when you put your foot down on the gas, this could be due to worn spark plugs.
Like any car part, spark plugs depreciate over time. When this happens, they have a harder time creating the spark that powers your engine. As a result, you may experience a loss of power, decreased performance, rattling or knock-like noises and poor fuel economy.
Spark plugs are relatively cheap, and with some mechanical know-how, it’s possible to change them yourself. However, since they play such an essential role in the overall functioning of your engine, you might want to have them fitted by a mechanic.
How much does it cost to fix worn spark plugs?
A spark plug replacement costs £159.17 on average when you book through FixMyCar.
7. MAF Sensor Malfunction
The mass air flow (MAF) sensor measures the amount of air entering the engine. It sends this information to the engine control unit, which adjusts the air-fuel ratio accordingly.
However, if the MAF sensor is faulty, it will likely result in a loss of power.
How much does it cost to fix a MAF sensor?
The sensor needs replacing, which typically costs between £150-200.
It can be a frustrating experience when your car isn't operating at full power, but the good news is that FixMyCar can help you find reliable local car repairs that won't break the bank.
If you found this guide helpful, you might also like:
- Related topics:
- Diagnostic
- Diagnostics
- Loss Of Power
Ellie is FixMyCar's Content Manager. She has over three years of experience writing about cars and regularly collaborates with automotive experts to provide trustworthy advice for drivers that is easy understand. Her work has been featured in Yahoo! Finance, iNews, The Daily Express and The Sun. She has a BA in English literature and an MA in creative writing from Durham University. Outside of work, Ellie follows F1 and eagerly awaits Ferrari's next era of dominance in the sport. She drives a Suzuki Swift.