There are pages of things that will turn the check engine light on. You need to have it checked for codes.
something wrong on the engine get it chek for any codes
Check the ignition coil, or the fuel pump.
check in this web site the-blueprints.com
Use an automotive computer code-scanner to read the stored code. Then you'll know why the "check engine" light is on.
The AT check signal light means that there is something is wrong with the transmission. A slipping transmission can be the cause of this.
Check the transmission fluid on the 1995 Nissan Altima. Bad fluid can cause the transmission to shift harder on parts that are more worn.
It is 1.0 mm to 1.1 mm or 0.039" to 0.043" You can check in the manual for Nissan 1997 Altima
replace fuel cap with Nissan only OEM replacement.
check for blown fuses
I think that depends if you have a check engine light on because of it. If the speed sensor is not working properly, the engine will not use gasoline as efficiently so there may be an emission problem