Mazda Repair: mazda 626, powertrain control module, independent mechanic

Question
car was not going in reverse so put in shop for 2 months.  found a tranny to put in . 2002 model my car is a 2001. also put a computer in . car was fine for a few days then had problems with shift to 1st and 2nd gears. also overdrive light comes on. what could be wrong? possibly sensor is bad? i think the transmission and computer is fine. should i bring it to mazda dealer to put on machine even though another independent mechanic worked on it.  

Answer
Hi Cynthia  Thanks for asking, With newer vehicles, I always recomend taking them to the dealer, there is a tremondouse amount of specialty tools required for newer vehicles. Especially when it come to electriacl work. And I think you are going to find you have an electrical problem. Private shops just dont have the accesbility to go into Mazdas Computers and reprogram the PCM (powertrain Control Module). It is usualy a bad idea to take a PCM out of another vehicle and put it in yours,, Unless  AALLLL  numbers on both PCM's match. If thats the case then it did not have to be changed. I know on the 2002 model protoget some updates have been done to the transmissions because of problems Mazda was having with earlier versions. The Mazda dealer will be able to tell you alot more. THey have the only computers that can read these PCM's.  It may be possible that that PCM just has to be reprogrammed to that vehicle.It is hard for me to give you a detailed answer without looking at the vehicle myself.
But I hope it was helpful
Good luck
Chris P