How to replace an engine air filter

When to replace an air filter

The air filter is a service item. Your vehicle manufacturer's service schedule says when it is changed: after a distance, after a time, at a particular service, or according to its condition or to a filter restriction indicator. As a rough guide from general practice, not a figure from our catalogue, an engine air filter is commonly changed every 15,000 to 30,000 km or every one to two years. Schedules differ widely between vehicle manufacturers and engines, and some allow considerably longer intervals, so the schedule for your vehicle decides. Many schedules call for an earlier change on vehicles driven in dusty conditions, such as unpaved roads or building sites. Where the vehicle has a service indicator or a filter restriction indicator, follow what the handbook says about it.

Whatever the schedule says, replace a filter when an inspection finds one of these, unless its maker's instructions expressly provide for cleaning, drying or treating that part and its condition allows it:

• The filter medium is torn, holed or crushed, or has come away from its frame or seal
• The seal is hardened, deformed, torn or missing
• The filter is wet, or soaked with oil or another liquid
• The filter is heavily clogged with dirt, leaves or insects
• The filter does not fit the housing, or is not one listed for the engine

Colour alone is a poor guide: a filter darkens in normal use, and a filter that looks clean can be due by the schedule. A badly clogged filter can reduce engine power and, on some engines, raise fuel consumption or cause a fault to be stored. These symptoms have other causes too, so a new air filter is not a diagnosis of them.

Replace a filter insert that is damaged or due for replacement by the schedule. Do not wash one, knock it out or blow it out with compressed air unless its maker's instructions expressly allow that for the part: cleaning can open holes in the filter medium that cannot be seen and that let dust through.

Before you start

Never run the engine with the air filter removed, with the housing open or with an intake hose or duct off. Depending on which opening is exposed, the engine can then draw in unfiltered air and anything loose near the opening, which can damage the engine itself and, where it has them, the air mass sensor and the turbocharger.

• Park the vehicle on level ground with the parking brake applied. Where the bonnet has to be open for the job, make sure that its stay or struts hold it securely. Switch off the ignition and keep the key or remote away from the vehicle, so that the engine cannot be started. Follow your vehicle manufacturer's instructions for service work on engines that start automatically and on hybrid vehicles, and disconnect the battery if those instructions call for it. An electric cooling fan can start by itself even with the ignition off: where the work brings hands or tools near a fan, keep clear of it and follow the vehicle manufacturer's procedure for preventing it from running. On a hybrid or electric vehicle, do not touch the orange high-voltage cables or the components they connect.
• Let the engine cool before you begin: hot parts cause burns, and on many engines the air filter housing sits close to them.
• Find out where the air filter housing is on your engine and how it opens. Housings are closed in different ways, for example by spring clips, by screws, by a cover that is turned or slid to release it, or by a combination of these, and some have hinges or tabs along one edge. Find out as well how the filter is held: it can lie in the housing, sit in the cover, stand upright or slide in on a holder of its own. On some vehicles an engine cover, an intake duct, the battery or other parts are in the way, or the housing has to come out of the vehicle, and the job is considerably longer.
• Find out what is attached to the housing cover. An intake hose, breather or vacuum hoses and the air mass sensor with its connector can sit on it. Some covers open far enough with everything attached; on others these have to come off first.
• Before you start, have the new filter ready, and obtain the vehicle manufacturer's procedure and any tightening specifications it gives for the housing's fixings, for hose clamps and for the parts removed for access.
• Work in a clean, dry place, out of wind and rain, so that no dirt or water gets into the open housing.
• Whenever the engine has to run after this job, first make sure that the vehicle stands in the open air and cannot move, with the parking brake applied and the transmission in neutral or in park, and that hands, clothing, tools and cloths are clear of moving and hot parts. Never run an engine in a garage or another closed space: exhaust fumes are poisonous.

Choose the right filter

Air filters differ in shape and size. Many are flat rectangular panels, others are round, such as ring-shaped and cylindrical filters, and some have a shape of their own made for one housing. They also differ in their seal and in the direction in which the air passes through them. A filter of nearly the right size does not seal: fit only a filter listed for your engine.

Select your vehicle with the selector on this page to see the part numbers listed for its engine. Where its supplier states them, each part number is shown with specifications such as the shape, the dimensions and the seal material. Where suppliers state a filter type for the air filters in the catalogue, they state a filter insert: the replaceable element that sits in the vehicle's air filter housing.

• Some part numbers are stated as with a pre-filter, a further layer that holds back coarse dirt ahead of the filter medium, and others as without one. Choose the version listed for your vehicle.
• Some part numbers are stated as being for dusty operating conditions. Fit one only where it is listed for your vehicle.
• Some engines have more than one air filter, and for some part numbers the supplier states the quantity required. Find out from the listing and from the vehicle manufacturer's information how many your engine has, and replace all of them together, unless the vehicle manufacturer's schedule treats them separately.
• Where more than one filter is listed for an engine, they can be equivalent parts from different suppliers or parts intended for different versions of the vehicle. Where a supplier states conditions for a part number, such as a production period, an equipment code or the OE number of the housing, they say which vehicles it is for. If what is stated does not settle it, ask the supplier or the vehicle manufacturer before you buy.

All air filter OE numbers in the catalogue

Remove the old filter

1. Before you remove anything, switch off the ignition, make sure that the engine cannot be started, as described under Before you start, and let the engine cool if it has run. Where the bonnet has to be open, make sure that its stay or struts hold it securely before you work under it. Then remove the engine cover and anything else that blocks access to the air filter housing, as the vehicle manufacturer describes. If access would mean opening the cooling system, the fuel system or the air conditioning circuit, or disconnecting a component of a hybrid's high-voltage system, that work has its own procedures and precautions: leave it to a workshop.
2. Wipe or vacuum loose dirt, leaves and sand off the housing and from around its joint before you open it, so that nothing falls in.
3. If the cover cannot be opened with everything attached, take off what holds it back, as the vehicle manufacturer describes. Unplug an electrical connector, such as that of the air mass sensor, only with the ignition off: release any clip or lock on it and pull on the connector, never on the wires. Release the clamp of an intake hose, and any clip or lock on a breather or vacuum hose, before you ease the hose off, and note where each hose belongs. As soon as a hose or a duct on the engine's side of the filter is off, close the opening it leaves, and the open end of the part itself, with a clean, lint-free cloth or a clean cover, so that no dirt, fixing or tool can fall in; keep count of every cloth and cover you use. Old plastic and rubber parts can be brittle: release each connection only in the way it is designed to be released, and do not lever it or force it.
4. Release the housing's fixings as the vehicle manufacturer describes. Release spring clips one after another; undo screws without dropping them, and note which stay captive in the cover. If the housing has a hinge or tabs along one edge, find out which way the cover has to move to come free of them.
5. Move the cover clear, in the direction its design allows, without straining the hoses and the wiring still attached to it. Where an air mass sensor sits in the cover or the housing, do not rest the cover on it, and do not touch the sensor's measuring element or let anything enter its opening.
6. Before you take the filter out, note how it sits: which face is towards the cover, which way round it lies, where its seal rests and, where the filter or the housing carries a mark or an arrow for position or air direction, where that mark points. Note any separate pre-filter, screen or insert in the housing and its position as well.
7. Take the filter out the way its mounting requires. A panel filter that lies in the housing lifts out of it; one that sits in the cover, stands upright or rides on a holder comes out with or from that part, as the vehicle manufacturer describes. A round filter is drawn off or out of its seat, after any cap, clamp or centre fixing that holds it has been released as the vehicle manufacturer describes. Move the filter gently and keep its dirty side from tipping towards the clean side of the housing, so that the dirt it holds does not fall in. Keep the filter for the inspection described below, on a clean surface away from the open housing.
8. Look into the housing with a lamp and find the outlet through which the filtered air leaves towards the engine. Where you can reach that opening, lay a clean, lint-free cloth over it for the time the housing is inspected and cleaned, and count it with the others; never push anything into the opening.

Nothing may fall into the clean side of the housing or the duct behind it: whatever lies there is drawn towards the engine on the next start. If something has fallen in and you cannot see and retrieve it completely, do not start the engine, and have it removed by a workshop.

Clean and inspect the housing

1. Before you clean anything, look at the old filter and at the housing for signs that air has passed around the filter: dust on the clean side of the filter or on the clean side of the housing. If you find any, look for the cause, such as a filter that was not seated, a damaged seal, a wrong filter or a cracked or warped housing, and put it right before the engine runs again. Dust that has reached the clean side may have reached the engine and, where there is one, the air mass sensor: have the intake checked by a workshop if there is more than a trace. Then put the old filter into a bag.
2. Vacuum the dirt, leaves and insects out of the housing, then wipe its inside and the surfaces on which the filter's seal rests with a clean, slightly damp, lint-free cloth. Unless the vehicle manufacturer's procedure expressly provides for them, do not blow the housing out with compressed air, which can drive dirt into the clean side and onto an air mass sensor, and do not use solvents or sprays in it. Let the wiped surfaces dry before the new filter goes in.
3. Check the housing and its cover for cracks, for broken clips, tabs or hinges, for stripped threads and for a warped sealing surface. Where the housing or its cover has a gasket or seal of its own, and where the connections of the hoses and ducts you took off have seals or sealing rings, check that each is undamaged and correctly seated, and replace any that is damaged. A housing that cannot close evenly all round does not seal and has to be repaired or replaced.
4. Check the duct that brings air to the housing, as far as you can see it, for blockages, and the intake hose and any breather or vacuum hoses you can see for cracks, splits and loose connections. A split hose behind the filter lets unfiltered air into the engine.
5. If the housing has a water drain or a dust valve, check that it is clear and undamaged.
6. Where the housing holds a separate pre-filter, screen or insert, clean, refit or replace it as the vehicle manufacturer describes, in the position it had.

Oil in the housing or on the filter can come from the crankcase breather, and on some engines a light film is normal while standing oil is not. Water can come in through a blocked drain, a damaged or displaced intake duct, or from driving through deep water. Find the source and have it put right: a new filter that becomes soaked with oil or water does not work properly either.

If the filter was wet through or water stood in the housing after driving through deep water, do not start the engine. Have a workshop check first whether water has got into the engine.

Fit the new filter

1. Check that the new filter is one listed for your engine. Then compare it with the old filter: shape, length, width and height or diameters, the form and position of the seal, and any pre-filter. Where they differ, do not fit the filter until its supplier or the vehicle manufacturer confirms that it is the right part. The filter that was fitted may itself have been the wrong one.
2. Check that the new filter is clean, dry and undamaged, with its seal complete and its filter medium attached all round. Do not fit a filter that is damaged or dirty, or one that has been wet, unless its maker's instructions expressly allow that for the part. If it has been dropped, inspect its filter medium, frame and seal carefully, and do not fit it if you cannot be sure of its condition. Do not oil it or treat it with anything unless its maker's instructions call for it for that part, and then only as they describe.
3. Take the cloth off the outlet, make sure that nothing else is left in the housing, and check once more that the clean side is free of dirt. Leave the cloths or covers on detached hoses and ducts until each is refitted.
4. Fit the filter the way the old one sat, following any mark or arrow for position or air direction on the filter or the housing and the vehicle manufacturer's instructions. If the old filter may have been fitted wrongly, go by the marks and the instructions, not by the old filter. A panel filter goes into the housing, the cover or its holder, wherever the old one sat, with its seal in or on its seat all the way round. A round filter is pushed fully onto or into its seat, and any cap, clamp or centre fixing that holds it is fastened again as the vehicle manufacturer describes.
5. Check the seating before you close the housing, as far as the design lets you see it. The seal must sit in or on its seat evenly all the way round and must not be folded, pinched, twisted or displaced anywhere: the seal around the edge of a panel filter lies evenly on its seat, and the seal at the end of a round filter is fully and squarely on or in its seat. On some designs the filter is held and its seal pressed home only when the housing is closed, and the seal cannot be seen afterwards: an evenly closed joint alone does not prove that the filter is seated, so make the checks the vehicle manufacturer describes for that design.
6. Refit the cover the way the vehicle manufacturer describes. Where it has tabs or a hinge, engage them first. On some designs the seal is pressed home by steady hand pressure on the cover or by fastening its clips or screws in the way the vehicle manufacturer describes, which is normal. But if a cover is out of line, meets an obstruction or will not go into place evenly, do not force it and do not use its clips or screws to overcome that: open it and look for a displaced filter or seal, a trapped hose or wire, or tabs that have not engaged.
7. Fasten every clip or lock, and tighten screws evenly, a little at a time and working across the cover, to the vehicle manufacturer's tightening specification where it gives one. The threads are often in plastic: overtightening can strip them or crack the housing. Afterwards the joint must be closed evenly all the way round.
8. Take the cloth or cover off each detached hose, duct and opening just before you join them, and check that nothing has got in. Refit each hose to the connection you noted for it, fully seated, and secure its clamp, clip or lock as the vehicle manufacturer specifies, to the manufacturer's tightening value where one is stated. Plug in every electrical connector you unplugged until its catch engages, and fasten again any separate lock you released on it, as the vehicle manufacturer describes. Route hoses and wiring as they were, clear of hot and moving parts.
9. Refit everything that was removed for access as the vehicle manufacturer describes, with new seals or fasteners where the manufacturer requires them, tightened to the manufacturer's values. If you disconnected the battery, reconnect it as the vehicle manufacturer describes.

Start the engine and check

1. Check that the housing is closed all round, that every hose and connector is back in place, that every cloth and cover you used is accounted for, and that no tool, cloth or bag is left in the engine bay.
2. Make sure that the vehicle stands in the open air and cannot move, with the parking brake applied and the transmission in neutral or in park; never run an engine in a garage or another closed space. Then start the engine. It should start readily and idle evenly.
3. Listen at the housing and the intake hose, keeping hands, clothing and cloths clear of moving and hot parts. A hiss or a whistle that was not there before can mean that a hose, a clamp or the cover is not sealing: switch off, let the engine cool, and check them.
4. If the engine runs unevenly, stalls or the engine warning light comes on, switch off, let hot parts cool and check that every connector you unplugged, such as that of the air mass sensor where there is one, is engaged and locked, that every hose is on its own connection, and that the filter and the cover are seated. If the fault remains, have it diagnosed before driving.
5. Where the vehicle has a service indicator or a filter restriction indicator that has to be reset after the change, reset it as the handbook or the vehicle manufacturer describes. Record the filter change in the service record, whether or not an indicator had to be reset.
6. Dispose of the old filter as your local waste rules require.

Mistakes to avoid

• Running the engine with the filter out or the housing open
• Letting dirt from the old filter fall into the clean side of the housing
• Blowing out the housing or a filter with compressed air where the manufacturer's or the maker's instructions do not expressly provide for it
• Fitting the filter the wrong way round or with its seal folded or pinched
• Forcing the cover shut, or using its clips or screws to pull it down, over a filter that is not seated
• Overtightening the housing's screws
• Leaving a hose, a clamp or an electrical connector off
• Leaving a cloth or a cover in the housing, a hose or a duct
• Fitting a filter that is not listed for the engine because it is nearly the right size
• Touching or spraying the measuring element of an air mass sensor