i own a 1991 525i with 4l30 auto trans. my trans shifts just fine for about 15 to 20 min of continous use, but then all of a sudden with no apparent failure it goes into trans program & stays on default mode which doesnt allow the trans to shift. it stays on 2nd -3rd gear. when this happens i have to park the car for about 2hrs , then i can start the car right up with no trans program appearing. once again it shift well for about 20min and once again i'm back to step one. thinking of replacing the trans cpu. any ideas guys???
note: trans was rebuilt about 3 mo. ago.