There are two methods for resetting the "service engine soon" light on a Nissan Altima. One method, which is the most convenient, is to use a code scanner, which you can purchase at any auto parts store. The code scanner will display the codes automatically and has an accompanying code sheet. There is also a manual way to display the codes and reset the computer -- you need to access a code sheet the decipher the codes. The trouble codes must be repaired prior to resetting the computer, because the light will just come back on as long as it sees the failure.
Pulling The Codes With a Code Scanner
Step 1 Plug the code scanner's plug in the on board diagnostics port under the dash, to the left of the steering column. Turn the key to the "On" position, without starting the car.
Step 2 Press the "Read" key on the scanner, and it will begin to display all the codes. Make a note of the codes for cross-reference. All codes are formatted, so they display a letter followed by four numbers.
Step 3 Cross-reference the codes with the code sheet. This can be found on-line or at an auto parts store. Repair all faults represented by the codes.
Turn the ignition key to the "On" position, without starting the car. Press the "Erase" key to erase the codes and reset the computer.
Pulling The Codes Without a Scanner
Step 1 Turn the ignition key to the "On" position, without starting the engine. Wait three seconds. Depress and release the gas pedal five times in five seconds, then let the pedal up. Count seven seconds and then depress the gas pedal and hold it down for 10 seconds. As soon as the service engine soon light starts flashing trouble codes, let the pedal up.
Step 2 Make a note of all the codes by counting the flashes. For example, if the light will flash four times in a row and pause for a second and begin flashing again, the first four flashes stand for the number 4; it will then proceed to the next number.
Step 3 Cross-reference these number codes with a code sheet. Repair all the faults before resetting the computer.
Reset the computer and turn the service engine soon light off by repeating the first process completely, with one exception: When the pedal is lifted after pressing the pedal down for 10 seconds and the codes are flashing, depress the pedal again for an additional 10 seconds and the computer will reset.
Things You'll Need: Diagnostic scanner
Warnings: Do not disconnect the negative terminal on the battery without an electrical backup, in order to keep the memories in all the computers and the radio. A battery backup is available at most stores. It just consists of a small 9-volt battery attached to a plug. This gets plugged into the cigarette lighter before the battery is disconnected. It has just enough power to keep the memories alive, so they will not need to be re-programmed.
