Yep code readers are a must. Even if you can’t do the repair you can take it in the shop and tell them the codes so that they can’t charge $40 for doing the same 1 minute test. Truly it took me one minute to determine it was time for a new gas cap last month. And just last Sunday one more minute to determine it’s time for some new spark plugs / coil Packs for my Mazda 6.
I have had a code reader for about 10 years now...someone lost it for me so instead of spending another $100+ or so for reader that can do most everything, including ABS issues, I switched up to a Mini ELM bluetooth reader from Ebay for $10 shipped.
I then bought Torque Pro for my smartphone for $5.
Not only does it work just as well, it has all these cool gauges, can give you your 0-60 times, show your turbo boost levels, etc. It's a way better solution than the standalone readers unless you can afford one of those $8,000 snap-ons or whatever.