Dead 5EAT?

Hi guys. I have a JDM 2004 Legacy 2.5 non turbo auto which is acting strange. The gearbox goes from first to second and lurches in to third, then the sport light flashes and I either have no drive at all or it's stuck in first.

 

Is the gearbox dead?

 

I pulled these codes using the OBD2 port:

 

P0733 - gear 3 incorrect ratio

P0734 - gear 4 incorrect ratio

P1718 - AT CAN communition circuit

 

The gear oil is dirty. Probably never been changed. Is it worth changing the gear oil or is it new gearbox time?

At this point (likely >100K miles on the slushbox right?) doing a drain-n-fill or full flush might do more harm than good (as debris gets dislodged and moves elsewhere in the plumbing or clogs something it shouldn't).

 

Can you reset the TCU and see if you can pull some TCU codes using FreeSSM (if that even works on a 2004)? Generic OBDII codes are usually fairly useless.

 

Implied gear ratio errors might hint at TC and various speed sensor issues inside the transmission sub-assemblies, the CAN communication circuit error alone could be causing all kinds of issues (including the behavior you describe) even if the 5EAT is still ok hydro/mechanically.

Thanks. I jump started a friends car about a week before this started happening. Coincidence or could I have fried something?