My cars automatic transmission has died at 157,000 miles. I was driving to work and all of the sudden a slight loss of power and the "service engine now" light came on. Felt like it was slipping but turns out it was stuck in a 3rd gear safe mode.

My mechanic said it could be just a solenoid, so we ran the codes and got a "P1757" fault. FR / B Solenoid Circuit. We tried popping in a new solenoid, cleared all the codes three times and drove it around. 1st, 2nd, and 3rd shifts no problem, but 3rd to 4th theres an audible noise, mechanic described it as similar to the sound of trying to get a manual car into reverse and grinding the gears a little.

My options are: try replacing the valve body for 400 + 350 labor (which might not fix the problem), or replacing the tranny with a warrantied used one for 575 + 750 labor. The warranty is for a year and covers parts & labor. Rebuild isn't an option due to crazy costs here in the L.A. area, costs ranging from 3K to 5K.

My question is: I found a 2006 G35 trans from a coupe that I would like to get, but Im not sure it'll fit my car. The part numbers are slightly different; 31020CM30 C/D (sedan) vs. 31020CM40 C/D (coupe).

Any insight will be appreciated!

 

I think the actual transmission model would RE505A.

Here is a video where a guy goes over that error code you have and fixes it. It's due to the circuit board coming loose if I remember right.