The cabin air filter cleans the air coming through your vents. When it clogs up, your air conditioning gets weaker, the car smells musty, and dust and pollen come straight into the cabin. It is also one of the easiest jobs you can do yourself.
How often?
Most manufacturers say every 12 months or 15,000 km. If you drive in heavy traffic, on dirt roads, or through a lot of pollen, replace it more often. Sydney drivers who park under trees usually need it sooner.
Signs it is due
Weak airflow even on the highest fan setting, a damp or dusty smell when you start the car, more fogging on the windscreen, or extra noise from the fan.
What you need
Just the replacement filter for your exact make, model and year, and about 15 minutes. Most cost between $20 and $50. You usually do not need any tools.
Step by step
1. Open the glovebox and empty it. On most cars the filter sits directly behind it.
2. Release the glovebox. Many have a stopper or small arm on the side — squeeze the sides gently inward so the box swings all the way down.
3. You will see a plastic cover, usually with clips. Unclip it and slide the old filter out. Note which way the arrow on the edge points — that is the airflow direction.
4. Have a look at the old one. If it is grey, full of leaves or smells bad, you found your problem.
5. Slide the new filter in with the arrow pointing the same way. Clip the cover back, lift the glovebox into place, and you are done.
Worth knowing
Some models put the filter under the bonnet near the windscreen, or under the dashboard on the passenger side. A quick look at your owner's manual will tell you which. If yours is one of the awkward ones, it is still a cheap job to have done at your next service — just ask for it to be included.
Carbon-activated filters cost a little more and do a better job with smells and exhaust fumes. Worth it if you commute in traffic.