About the only vestiges of the traditional tune-up still around today are replacing your engine air filter and spark plugs, and neither is likely to void your warranty. With spark plugs, chances are your warranty will expire long before it’s time to replace them.
On some cars, such as Volkswagens, the fuel filter has to be replaced every three years (even more often on diesel models), which could be considered part of a tune-up, but we recommend leaving that job to a pro.
Replacing the air filter is a 5- to 10-minute job on most vehicles, though on some cars its location is such that you may have to loosen or move other components to get at it. Once you do get to it, just remove the old one, wipe out any dirt or debris, and put in the new one.
What could go wrong? Well, you could use the wrong filter, install it the wrong way, not close things up entirely or damage the air intake system. If any of those issues were to allow dirt inside the engine, over time that could damage internal parts that operate under close tolerances and need to be clean. If a dealership was able to connect the internal damage to a bungled air-filter installation, that could void the warranty no matter who installed the air filter.
The above scenario is unlikely, though, and it’s a good idea to change the air filter every couple of years (maybe sooner in urban areas or dusty places). If you have any doubts about your ability to do it, though, you’ll be better off paying someone who knows how.
As for spark plugs, some manufacturers call for them to be replaced as soon as 30,000 miles, but on many cars it may not be necessary until 100,000 miles or more — after your extended powertrain warranty has expired and even after many extended service contracts end.
More things can go wrong with badly installed spark plugs than with an air filter: Damage to ignition wires or coils during removal or reinstallation, breaking a spark plug while trying to remove it, cross-threading a plug while installing it, or over-tightening so that it damages the thread and/or cylinder head. If any of that happens, the damage will not be covered by your warranty, though it wouldn’t necessarily void it, either. You’d probably just have to swallow your do-it-yourself pride and pay the repair bill.
Remember: Even if your warranty isn’t at stake, you don’t want to bite off more than you can chew.