I recently got a P1772 code for my 2003 G35 coupe with about 158k miles. I thought I'd share what I learned about fixing it since I could find very little info on the subject. This should apply to any broken solenoid on the valve body. I believe the valve body was updated for the 05 model year so your mileage may vary.

Basically the code said that it was either a wiring issue or that the solenoid itself was bad. After trying to determine that myself I caved and brought it to a mechanic for a diagnosis. He tested all the wiring, the solenoid, and the tcm. Ended up being the solenoid. Mechanic wanted $2800 to replace the entire valve body with an oem one. I was fairly certain that you could just replace individual solenoids on it but he was confident I could not. I decided to give it a whirl myself to try fixing it and it ended up working. I did this all in my driveway on jackstands and didn't use any fancy tools. Pretty much just a 10mm socket wrench was the only thing I really used. It didn't take much to do. Here is how I did it.

I bought a pack of 7 new solenoids so I could replace all of the ones on the valve body. I also bought a new transmission pan gasket, transmission filter, drain plug gasket, and new matic S transmission fluid.
First step is to drain the transmission fluid and disconnect the battery.
Second remove the transmission pan. (I am not going to give detail on these really basic steps because there is already info out there on them and this would take forever if I did)
Third remove the 12 bolts holding the valve body in place after disconnecting all the wiring. Take photos as you go and note where the bolts go as they are different sizes.


Valve body before removal

Fourth, Identify which solenoid you are after replacing. In my case it was the odd one out on the far right side. Note that there are only 3 types of solenoids on the valve body. 2 pairs of 3 and one solo. The ones that look the same are all identical.

This shows 6 of the 7 solenoids on the valve body along the bottom. I had already removed the Low coast brake solenoid on the far right side. Each one is held in with an allen key

5th step is to replace all of the solenoids or just the one you know is broken. Just unplug the old one and carefully plug in the new one. Take your time and don't damage anything on the valve body as it is a very expensive part.
6th step is to replace the transmission filter. just remove all the nuts and bolts holding it in and put a new one in place. The torque spec is 70 inch pounds.
7th is put the whole valve body back into the transmission and torque all the bolts down to 70 inch pounds. Try to evenly torque them down.
8th. Probably the worst part of this whole thing. Carefully scrape the old paper gasket of the transmission pan. The only way to do this is to use a razor very carefully as to not scrape or cut the pan. Also using a sharp plastic edge like plexi glass or something helps. Take your time and don't damage the pan. If you make it leak a new pan is about $100 Chemicals do not work on this stuff. I tried using every solvent in the house and nothing worked.
9th is to clean the pan and the 2 magnets at the bottom to remove any metal bits.
10th is install the new gasket torqueing the 4 bolts in the corners first in a crisscross pattern to 70 inch pounds. Next torque all the bolts around the edge moving in one direction starting from the rear passenger side of the car if I remember correctly. I also used blue locktite on all the bolts holding the pan since it looked like there was locktite on from the factory. I also cleaned all the bolts in vinegar before re using them.
11th is to install the new crush washer on the drain plug. Torque the drain plug to 25ft pounds using a 19mm socket.
12th is to fill your transmission up from the dipstick hole. If you can, measure how much fluid you drained initially including what came out of the valve body. I ended up needing 7.8 bottles (946ml each) of the stuff to fill my trans up to the correct level. There is a substantially more amount of fluid that comes out when you drop the trans pan and valve body than in a normal transmission fluid change. Also make sure you measure your fluid level correctly. Nissan made it way more complicated than it needs to be and it is easy to measure it wrong.
13. Check for leaks and take it for a test drive. If it sounds wrong it probably is wrong. Don't blame me, I am just sharing what I did and what I think works.

After doing this my service engine light was gone and so far I have driven about 100miles and the light has not come back. The car runs great. I will update this post If something changes. All in all this cost me only a few hundred dollars plus the mechanic diagnosis. Much cheaper than the $2800 my mechanic wanted.

Here is a link to the parts I got
Solenoids:

Filter and gasket (gasket can be bought at a dealer also):

Fluid can be bought at a dealer. They replaced matic J with matic S. Just ask them to give you the right fluid for you specific car.

Drain plug gasket can also be purchased at the dealer.


Here are some youtube videos I found helpful:



Update*
I just did a 500 mile road trip through the mountains and everything still works fine. No check engine light and no visible issues.

 

Great pictures and information!
Yes, so FYI for anyone that is reading this: mid-year 2004 Nissan changed the design for the valve body/wiring harness for the RE5R05A in G35's and 350Z (I'd imagine similar for other models too, fx35, etc). This transmission was a go-to for Nissan!
Early cars (all '03 and 'early-04') have the TCM located externally in the passenger side lower kick panel, like aktazf has. Your transmission has 3 electrical connection pigtails to the chassis harness.
'Late-04' or 2004.5 cars and newer have the TCM internally within the valve body inside the transmission, like the videos linked at the bottom. Your transmission has 1 electrical connection to the chassis harness.
As I understand, the later cars have the AT shifter with the release button on the front towards the radio (hint for identifying which '04 you have), while older cars have the shift button on the side (thumb actuated).
For the late-04 + cars, there is contact point that can crack or break causing the same or similar DTC's OP had.
Not sure if the solenoids are the same for either valve body design.
For G35X of this vintage, I don't where the TCM is located.

 

Also, for those who do this, I'd buy the OEM pan gasket. Its priced quite close to anything you'll get from local auto parts stores, but much much better quality.

 

There are actually 4 different valve bodies (different solenoid resistances), Sonnax has a great website with pictures and such. Early model had two different low coast solenoids, newer model had two different low coast solenoids.

https://www.sonnax.com/parts/4156-re...red-valve-body

https://www.sonnax.com/tech_resource...identification

 

Yes that is true. I ended up using an oem gasket that was about $30 since the one I ordered was taking to long to arrive. However you cannot buy a transmission filter from the dealership since they claim it is non serviceable.

 

It's not serviceable, it's just a metal screen that's mounted up above the TCM/valve body.

 

Yup, not much point to replace the 'filter' unless you really wanted to inspect it
I run a magnefine 5/16 inline filter in the trans lines. They work pretty well in my experience.

 

I was able to remove and clean mine with some rubbing alcohol. It wasn't really dirty but could have been replaced if needed. They may have moved it or changed how it is attached in the later models when the TCM was integrated into the transmission.

 

Heres the valve body off my 05 coupe

 

for the other pairs that are 3 and 3, does it matter which order they go in?. I took them out yesterday and forgot which order they went in. I dont know if the ones that look the same can be placed in any order. Or they have to go in a specific order.