my 05 s type keeps trowing code 738 and my trany fluid is kleen and not sliping please any suggestins

 

i have a 05 s type with a 3.0 engine with a zf transmisson automatic my gear box defalt light goes on car gets stuck in limp mode i turn it off and start it agin goes off cars fine for few days and then does agin i read the code it is 738 and now the engine light stays on tll idiscnet battrey . any way tras fluid is clean no slipeige but 3rd and forth shift the tacomter does raise between thes shifts a littel not much do i need to ter it down or can i get by with it for awile please any help