Found this and thought I'd share!
The following applied to a 2004 Nissan Altima but I believe any Nissan uses this method.
The Service Engine Soon light will come on and stay on when the onboard computer detects a problem with your car. When a problem arises, a unique engine diagnostic code or codes will be stored. It is fairly easy to pull the code that was stored. Follow the steps below and the Service Engine Soon light will flash a sequence that you can convert to a numerical code. Note that the timing on the steps below must be very accurate. I made several unsuccessful attempts before finally resulting to using a stopwatch to time it. With the use of a stopwatch, it was quite easy to get the timings right.
- Turn the ignition key to the on position for exactly three seconds.
- Push the accelerator pedal all the way to the floor and release 5 times within 5 seconds.
- Wait exactly seven seconds.
- Push the accelerator pedal all the way to the floor and hold for ten seconds
- As soon as the Service Engine Soon light flashes, release the accelerator pedal.
At this point the Service Engine Soon light should start flashing the error codes that are stored in the system and you can release the pedal. If you only get five slow flashes, or any sequence of flashes that does not correspond to a 4 digit code, or no flashes at all, then your timing was off on one of the above steps and you should start over.
When the Service Engine Soon light starts flashing you count the number of flashes (1-10, with 0 10 being 0). There will be a 4 digit code. The first flash is about .5 of a sec the next three are approximately.3 sec. After the 4th sequence is flashed, it will begin flashing the sequence again with a sequence of slow, .5 second flashes. The lights will continue to flash the sequence over and over again.
For example, 10 slow flashes followed by 3 quick ones, 10 more quick flashes, and finally 5 quick flashes, corresponds to engine code P0305.
Note that you can clear the code(s) too. To clear the codes, push the pedal all the way to the floor and hold for at least ten seconds. The light will continue to flash and there’s no indication that the codes have been cleared so make sure you time ten seconds or more.