CarMD has revealed its second-annual vehicle health index report, and the overall finding is that putting off auto maintenance can be a costly proposition in the long run.

Among other things, the index tracks which repairs are most common at garages across the country. The report is limited to repairs that cause the "check engine" light to come on. All of the repairs are quite common and relatively inexpensive to perform, and many can even be accomplished by an amateur mechanic. However, the report found that many Americans ignore their check engine light and put off these repairs, often costing themselves money in the long run.

The top repair on the list is a prime example: replacing the oxygen sensor. This is the most common reason for a check engine light to come on, but many drivers will keep driving as if nothing is wrong. That's a big mistake, as a faulty oxygen sensor can reduce fuel economy by up to 40 percent, causing the driver to spend a lot more at the pump. It's much more affordable to get the sensor fixed. In fact, those who are driving older vehicles that have never replaced the sensor may want to replace it pre-emptively in order to ensure their fuel economy remains top notch. The second most common "check engine" problem was a loose gas cap, which will cause fuel to evaporate and similarly increase the cost of filling up.

Another set of issues shows how a minor repair can quickly snowball into a major one. The third most-common repair on the list was replacing the catalytic converter. Unlike the oxygen sensor, this will likely cost quite a bit to replace - possibly even over $1,000. However, it's a problem that's easily prevented by those who pay close attention to their cars.

The sixth-most common problem is replacing a bad spark plug, which is a really simple and cheap repair that anybody can do. But ignoring the spark plugs can in turn damage the ignition coils - which got on the list as the fourth-most common issue. And the ignition coils in turn lead to a faulty catalytic converter. So while the catalytic converter is an expensive issue, it's largely only because people ignore their spark plugs and ignition coils - repairs that are much easier on the wallet.