Cabin filters, also called pollen filters, clean the air coming into the vehicle through the heating and air conditioning system, trapping dust, pollen, soot and road grime before it reaches the occupants.

This is the filter most often forgotten at service time, and a blocked one causes problems people rarely connect to it: weak airflow from the vents, windows that take forever to demist, a musty smell when the fan comes on and an air conditioner that seems to have lost its performance. Replacing a clogged filter frequently fixes all of that for very little money.

Most vehicles need one every 15,000 to 30,000km, and sooner in dusty conditions or heavy city traffic. Fit it the right way round, since the airflow arrow on the frame matters, and check the housing is clear of leaves and debris.