2008 Chrysler Pacifica
 

Hello... I have a 2008 Chrysler Pacifica LX it has a 4.0 liter I'm having a problem it will only stay in 1st gear "Sometimes" the check engine light is on I took it to my mechanic he said it has low voltage code but he don't due transmission work so I took it to a transmission shop and they said it could be a transmission oil cooler lines "$435" it drove the first day great it rained very hard I got up next day and went to drive it check engine light is back on it wouldn't shift outta 1st gear again!! I got home shut it off & started back again and it shifted fine but check engine light is still on!! Also the radiator fan runs constantly as soon as I start it even when engine is still cold. Does anyone have any ideas what could cause this??

having the code number you got would be some assistance