I have a 2003 Accent with auto tranny. For some reason the tranny will shift out of highway gear and drop down to a lower gear. After I shut the car down for a few minutes and then restart, all is ok. it will be that way for a few weeks and then do it all over again. Any suggestions on what may be the cause.

 

Got MIL ?

Got codes ?

If you find an output speed code, test sensor first, (TSB for concern).. if sensor good, program TCM...... if sensor out of spec,,, replace sensor and program TCM...

There is host of other programs you may be lacking to bring engine and trans modules up to date

 

I am not getting any lights coming on, vis a vis service engine light. I do have a scanner and will see if any codes come up