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Maintenance and tyres , Costs and money , Know your car · Actualizado el 2026-10-18

Air filter and cabin filter: what they do

A car has more than one air filter, and they do very different jobs. One protects the engine and the other protects you. Both are cheap parts that are easy to forget, and both are often among the simplest items to replace. Understanding them can save you money on service quotes and stop you paying for work you do not need.

The engine air filter

An engine needs a large amount of clean air. The air filter sits in a box in the engine bay and stops dust, pollen, insects and grit from entering the engine, where they would wear the cylinders and sensors. The filter is usually a pleated paper or fabric element that traps particles as air passes through.

Over time the filter fills up with dirt. A heavily clogged filter restricts airflow, and the engine may lose some power, run less smoothly or use more fuel. On modern engines the effect is often small, but a blocked filter in dusty conditions can cause real problems.

The cabin filter

The cabin filter, sometimes called the pollen filter, cleans the air that enters the passenger compartment through the heating and ventilation system. It traps dust, pollen and some soot particles. Some versions include activated carbon to reduce odours. Not every older car has one; check your manual.

A dirty cabin filter often shows itself in several ways:

• Weak airflow from the vents even at high fan speed.
• A musty or sour smell when the fan or air conditioning starts.
• Windows that mist up more easily and take longer to clear.
• More noise from the fan as it struggles to push air.

Allergy sufferers notice the difference most, and a clean filter is a simple way to make long drives more pleasant.

How often to replace them

The interval is in the service schedule, as explained in how often to service. Typically the cabin filter is replaced more often than the engine air filter, and both sooner if you drive in dust, near construction, on gravel roads or in heavy city traffic with a lot of pollution or pollen. When in doubt, look at the filter. If it is grey or black, full of leaves or debris, or smells bad, it is time.

What you can do yourself

These are among the friendliest jobs for a beginner, if your car makes access easy. Check the manual or a video for your exact model first.

1. Buy the right filter for the exact car and engine, using the parts catalogue or the old filter as a reference.
2. Switch off the engine and open the filter housing. The engine air box usually has clips or screws; the cabin filter is often behind the glove box or under the bonnet near the windscreen.
3. Note the direction of airflow, which is shown by an arrow on the filter.
4. Remove the old filter and wipe any debris from the housing without letting it fall into the intake.
5. Fit the new filter the same way, close the housing and make sure all clips are secured.

If something looks unfamiliar, or access needs dismantling other parts, a workshop will do it quickly. Never run the engine without the filter or with the housing loose, since unfiltered air damages it.

Cleaning versus replacing

Tapping out a paper filter may give a short improvement, but it does not remove the fine dirt and can damage the element. Washing a paper filter is not recommended. Some performance filters are designed to be cleaned and oiled; follow the maker's instructions closely, because too much oil can contaminate sensors. For most owners a standard replacement is the simplest and safest option.

Other filters you may hear about

Oil, fuel and, on diesels, particulate filters are different parts with different rules. The oil filter is replaced with every oil change, as described in engine oil explained. Fuel system work, including fuel filters, is not a job for beginners. Leave it to a workshop.

Reading the service quote

Filters are sometimes listed as extra items. It is fair to ask when each was last changed and whether the interval is due. If you are told the filters are "dirty" ask to see them. Honest workshops are happy to show you. Compare the price of the part with the labour, because the part is usually inexpensive. See finding a good workshop for how to judge a quote.

Buying a used car

A service history that shows regular filter changes is a good sign of care, while a very dirty cabin filter suggests neglect or a car used in tough conditions. It is a small point, but it tells you something about how the previous owner behaved. Keep your own records in My Garage.

What to remember

• The engine filter protects the engine; the cabin filter protects the air you breathe.
• Weak airflow, musty smells and misting suggest a tired cabin filter.
• Replace both on schedule, and sooner in dusty or polluted conditions.
• Both are usually simple jobs, but do not run the engine with the housing open.
• Replace, do not wash or tap, ordinary paper filters.

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