I have a 97 nissan maxima, it was serviced in february but the service light stays on. why is the service light staying on?

replace the IAC sensor , then use a scanner to reset the ECM

Here's the link and I'm sure you will get the solution of your problem 1997 Nissan Pathfinder Service Repair Workshop Manual INSTANT DOWNLOAD

YOUR ALTERNATOR IS NO GOOD TRY UNHOOKING THE POSATIVE CABLE MAKING SURE NOT TO LET IT TOUCH ANY METAL SURFACES IF IT DIES TAKE ALT OFF ANDHAVE CHECKED TO CONFIRM HOPE THIS HELPS REPLY BACK

You need to take the battery and have it load tested.

Visit the on-line store, know as reliable-store, they have the repair manuals. I'm sure you will get the solution of your problem.
Nissan Maxima Factory Service Repair Manual 1994 2009

code p 0138 refers to 2 items
1--heated oxygen sensor(HO2S) 2 bank 1--high voltage ==causes --wiring short to positive --HO2S---ECM
2--oxygen sensor (O2S) 2 bank 1--high voltage ===causes wiring short to positive ---ECM
code p 0139 refers to 2 items
1--- heated oxygen sensor (HO2S) 2 bank 1--slow response ===causes --heating inoperative --wiring--ECM
2--oxygen sensor (o2S) 2 bank 1 slow response ===causes --wiring --- O2S

heated oxygen sensors9HO2S) are in the exhaust manifold before the cat converter
Oxygen sensors (O2S) are after the cat converter
it is indicated that the HO2S is faulty-
check the wiring and /or replace both sensors

You need to have the system tested for trouble codes, Kragen and Autozone parts stores do this for free.

brake light switch stuck or bad

I'm going to need more information. Does the peddal feel the same? Do you have any weird vibrations? My first feeling is that your Throw out bearing is bad, in which case you will need to replace the clutch. Second is that your Hydraulic system on the clutch has a leak or is dry. let me know.