When your auto car have the problem with emission systems, your car let you know by turning on check engine light. And then you need to take your car to your local mechanic service station. The first thing that the mechanic have to do is to plug something into a connector under the dash. From there, a cord leads to a handheld electronic device. A mechanic looks at a display of the device.
Now mechanics can show the roughly where the problem lies. Then they begain to solve the problem. Some of procedure need additional tools or trained skills, but usually the first a few steps of overall procedure is simple. Like 'see if a gas cap isn't loose' or 'check the parameter of a certain sensor (done by the same handheld device)'
This device is that used was called OBD2 scantool. Depending on models, scantools can read trouble codes, erase trouble codes, and monitor various sensor's parameters. It would be very nice to get all information all the time, check codes and try to do some easy repair for yourself. However, scantools are expensive. The most sophisticated scan tools cost thousands of dollars. These scantools are for mechanic shop owners. Besides, these scan tools may need periodic update by changing chips or cartridges. And that may cost over and over.
On the other hand, cheap scan tools can do much. For example, around 50 dollars scan tool simply shows code numbers without even descriptions. So middle range is recommended but they still cost hundreds of dollars. You may think it wouldn't be worth to own scan tools anyway.
But todady, you have the another option. You can use your laptop or smartphone as a scan tool. For it, you will need an adapter that connects between PC or smartphone and DLC and also software compatible with operation systems. There are many software and they provide trial versions or free versions. When you need to update, simply update software that may not cost at all. As for adapters, they relatively inexpensive. Depending on makes and models, the price range is 20 dollars to 150 dollars. And there are some extra features. It also shows 1/4 mile time, fuel economy, etc.
I used to ride a motorcycle. I've read many magazines about the motorcycles. All those magazines said something in common. They emphasized the most importamt thing is to keeping your machine clean and you may find a problem soon and easily. The same story here, Keep taking to your car periodically. When something happens you could react quickly. That will lead a lot of saving on auto repair.