Hi. I have a '99 Nissan Maxima SE that I just bought. Every Two days after I get gas the Service Engine Soon light comes on. The only way to turn it off is to reset the computer. I am putting in 91 octain gas and turning off the car when refueling. Any hints why this is happening?

 

Check Engine Light = Service Engine Soon light = Malfunction Indicator Light.
Three names for the same thing.

The Check Engine Light is evidence that something is wrong. That
"something" may be any number of things, some major and some minor. It
might be nothing more than a loose fuel filler cap. The Engine Control
Module (the computer) detected a problem and turned on the Check Engine
Light. At the same time it stored one or more Diagnostic Trouble Codes.
Get someone to do a DTC readout for you. This is not a big deal, does not
require specialized "dealer only" test equipment, and should take less than
an hour. When you know the stored DTCs, you will have a fair idea of what
repairs are needed.

If you like to do your own "wrenching" you can do the DTC readout for yourself.
No special tools are required.

You will find instructions to do a DTC readout and reset
the Check Engine light at:
http://vbxmaxima.8m.com/ecu.html

The DTC "translations" are found at:
http://vbxmaxima.8m.com/ecudecoder.html