The box you are looking for is right behind the battery. The box is small...........about two inchs long by three inchs wide. There is a plastic cap that covers the box which houses the diagnostic plug. Pop the plastic top off with your fingers and you should see a multiple pin connector. On the face of the connector is a little led/push button. With the ignition ON, depress the push button for 4 to 5 seconds and then release it. The button is actually an led and will begin to flash. Count the number of flashs, and then determine the fault that is associated with the number of flashs. When the led finishs a flashing sequence, once again depress the led/push switch for 4 to 5 seconds. If the led begins to flash, there may be a second code stored. If it flashs the same number of flashes as your previous try..........then you know that there is only the one code stored. If it flashs a different number of flashs....then you know that there are at least two codes stored. Continue to repeat the swtich reset sequence as above until you come back to the first code that you read.
The codes that can be read with the led are the only codes that will trigger you CHECK ENGINE light. Other fault codes for other problems are stored on the other pins of the connector; but, you will need the little LED tester that has been discussed on this board before.