I find several things very alarming here.
One is that the light came on and you refused to pull over and find out what the problem was and two that you refused to have the problem diagnosed or repaired by a trained technician. Stores such as Pep Boys will scan your vehcile for you for free. Most of those people, although not certified as mechanic's or properly trained to diagnose your problems can usually give you their opinion as to what your problem may be - since they do it all the time for people like you.
Most codes that flashes a check engine light usually involves the emissions, due to the fact that your vehicle will still run even when the light is on.
But the problem is that even though it runs, the computer usually puts the vehicle into the limp mode and it will run rough and get terrible gas mileage.
Most scan tools works on the precept that you plug the tool into the port under the dash board. You then turn on the ignition key to the on position - but you do not start it. Once the scan tool recognizes the port, it will go into a main menu and will ask what you care to do.
By pushing the read codes button, it will display the first code in the computer. Your job is to write that code down on a piece of paper. Then procede to read all the other codes in the computer. When you get to the end of the codes, the computer will ask you - do you want to erase all codes.
Your answer should be YES!
Because of your refusal to have the vehicle properly diagnosed when the light first came on. You might find that you have codes that has nothing to do with the origional problem. As you drive in the limp mode, other codes will surface ( snowball) the longer you drive it.
Just think of the LIMP MODE as walking on a fractured leg. If you were on the top of a mountain, with no way down except to walk, You could walk on a fractured leg, it might not be pleasant and you might not make good time and you could do more damage to the leg and the bone the longer you walked on it, but you could walk. At the same time, you could not run a marathon or play professional football with a broken leg. That is how the LIMP MODE works.
Usually the LIMP MODE will involve advancing the timing of the ignition and making the fuel mixture rich so as not to damage the engine while you drive it in that mode.
There are some very common / ordinary codes that usually surface once you clear the codes. In the old days, the most common code was for the oxygen sensor. Today most oxygen sensors will go for 100's of thousands of miles as long as you do not put fuel injection cleaner ( junk ) in the gas tank. Most oxygen sensor codes are now triggered by a faulty catalytic converter.
Low voltage or two sensors that has the same readings - which triggers a code which will say that catalytic converter below nornal threshold.
The second set of codes usually involves a sensor on the motor, the trick is knowing which sensor it is.
The third set of codes usually involves a leak in the fuel system. Be it a hole in a line, hose, a hole in the gas tank or a bad purge solenoid valve or evap cannister. If that is the code, the vehicle will still run and might not even go into the limp mode, but the light will come on every time you go to wide open throttle and everytime the tank falls below half full. It is a very dangerous situation and is almost never due to a loose gas cap or bad gas cap. For the most part - that is just wishful thinking.
Usually it will involve going to a GM garage and having the problem diagnosed and might involve using a sniffer to find the leak.
Either way, most of these repairs cannot be done by a shade tree mechanic with a cheap set of tools. Even a good / cheap scan tool that reads and clears the codes might be $150 or more.
Read the codes and come back and tell us what they are.
