The exact process of a tune-up can vary between service providers, but some common components are an engine condition check, replacement of spark plugs and filters, and testing of the oxygen sensor. An oil change is also usually included if one has not been done recently.
The engine is usually checked for safety and performance. A mechanic tests the battery voltage, power balance, engine vacuum, idle speed and ignition timing. Exhaust emissions may also be checked in states with clean air standards.. Fluids, hoses and belts are inspected and replaced if necessary. Spark plugs, filters, and rotor or distributor caps are also often replaced.