Volvo: 93 850 n/t flashing arrow questions, tranny fluid, solenoids

Question
My car has had the flashing arrow for awhile now.  I had the pnp switch changed when it first started but the arrow came back.  The mechanic switched it out with another one which the arrow stayed off for about 30 min. and came back on.  The car runs fine and the arrow doesn't always flash, it comes on most of the time and then sometimes not, or it will go off while I'm driving--whenever we switched out the pnp it would stop for a while. We also changed out the tranny fluid and it looked fine, no burnt smell, could still see through it. I'm getting code 323 from A1, I have read all the codes and (I think)cleared them but it is still there.  What does 'lock up slips or is not engaged' mean?  Do I have to get a new tranny?  Could it be a sensor?  The nearest person to look at my car is 200mi away.  Please help me!!  
Thank you for your time and answer
Angela

Answer
Angela,
The lock up feature is an internal part of the trans. There are solenoids inside the trans and most times they are the problem. They are tough to replace and most tend not to replace or repair that trans and just exchange it with a used or reman unit.