Hi,

I have 2001 nissan sentra QG15 engine w/automatic transmission. Sometimes the transmission wont shift for example it will stuck if first gear and not shift to 2nd. If i restart the car it will operate normally. I dont have any CEL. I flushed the transmission and replace the filter but no luck .

mac,there ought to be a transmission "Diagnostic" procedure , a basic "on vehicle test" - not needing the CONSULT Dealer Diagnostic system.Whereas it would be a sequence of "key-in", "key to ACC", key to ON",shift D,gas pedal to floor, pedal release, shift up, shift down, etc. Any of all or some of these ,done in a VERY SPECIFIC way following the correct EXPLICIT instructions in Svc. manual - RESULTS show as the MIL flashes -Long/Short(Svc. eng. Lt.) This is a very basis to START.
For I've just changed my J's trans fluid and FIRST I did this exact check for it would have shown up possible,problems ie. ,Trans ctlr.(TCM) , solenoids,trans temp sender,inhibitor Sw. , etc.
You probably have ALL Diagnostics in what's called your OBDII( On-Board Diagnostics TWO) system which MAY cover / include / & or supersede what I just described - due to the 2001 year model. Mine being pre- OBDII a '93.