CHECK ENGINE LIGHT;
Yes it could mean that a tune up is in order since a very dirty air filter can cause the check engine light to come on as can a number of other issue's inside your vehical.
This is a error code sent by the computer in your vehicle! It is reporting that one of the vehicles sensors that monitor its functions has found a problem and is sending information that is incorrect. This is usually because something has failed and no longer operating within the specified parameters that are required by the particular sensor or device. These readings are compared to values preset into the cars computer from the factory. An error code is a number from 0 to 50 usually (depending on the make and model of your car). Each of these codes tells the technician what area of the vehicle that is sending the error code from and the devices that operate in it. There is a specification book with all of the codes details for that particular vehicle that the technician uses. This is how he knows what a particular code is and what it means. This information can also be found by googling, and on certain automotive sites online. A certain code such as 35 (example only) might mean that the air fuel ratio is off indicating a number of devices that may be at fault that deal with that particular error code for instance. An oxygen sensor is often the culprit for this code, but not always. In an older vehicle a Mass air flow sensor for example could be the problem and sometimes both? There are other things that can make an Oxygen sensor malfunction as well. Any modern garage today has a machine or a scanning tool that they hook up through a connection in your vehicle called an ALDL that will read the error code number. From these readings using the scan tool he can determine what the source of the problem is. If you think that this check engine light might be due to a false signal (sets a soft code) since everything else seems to be fine you might try disconnecting the negative battery terminal for at least 20 seconds to clear the codes set by the computer. Be informed it will also reset any clocks or equipment that is preset as well. If there really is a problem with your vehicle the check engine light will come back on.
Some additional information,
When you start your vehicle in the morning or when it is cold (not warmed up) the computer in your vehicle uses preset values to operate the vehicle. This is called "open loop." When the oxygen sensor heats up to certain point it causes the computer in the vehicle to go into what is called "closed loop" and it starts using the values being sent from the sensors themselves rather then the preset values from the computer to operate. There are sensors that monitor a variety of systems in the vehicle from Crank shaft sensors to Throttle Position sensors, Knock sensors, Water temp sensors, oil sensors and many many more. All sending the computer information about the condition of your vehicle. The computer in turn sends back information for correction thousand of times a second, but can only make up a narrow margin of error. If the specifications being sent by the sensors is to far out the computer cannot fix or correct this and a trouble code is set resulting in the check engine light coming on indicating a problem.
Some auto parts stores like Auto Zone will read the trouble code being given by your vehicle for free if you take your vehicle by one of their stores. They do this as a customer service in hopes of selling parts if you need them. It is a good way of determining what is going on if your not savvy about such things and want to save some money in repair.
Their have been computers in US cars since the early 1980's. The computers used in today's vehicle's are state of the art.