Hey everyone!

Car: 2012 G37S sedan
Wanted to post this to help others that may run into the same issue as me.

Drive home and from stop light, car struggled to get through 1->2, 2->3, needed considerable high revs to do so (~4000rpms) and jerked into gear when it did. Wouldn't go above 3rd gear. Stopped, restarted car, same problem. Restarted 3rd time, cel comes on, same problem. Thankfully was only a about 2 miles from the house and was around 1am so empty roads (I love out in the country so that helped as well) and limped it home.

4 codes pulled:
-P0500 (vehicle speed sensor)
-P0720 (output shaft speed sensor)
-P0732 (2nd gear incorrect gear ratio)
-P0733 (3rd gear incorrect gear ratio)

The combination of these codes is important to narrow down the issue:

-P0500 WITHOUT a P0720 and WITHOUT gear ratio codes (p0729-p0735, p1734) will most likely NOT be a TCM/valve body/Transmission issue and has to be explored in depth outside on the transmission area (wheel speed sensors, harness/electrical issues (mainly water intrusion somewhere), throttle position sensors, MAP, etc.).

-P0720 alone or with other transmission codes and/or p0500 is almost guaranteed to be a bad TCM and not the actual output shaft speed sensor. It is possible getting only p720 alone or with p0500 can again be an electrical/harness (water intrusion) issue, but that seems quite rare and would most likely involve other electrical issues/codes (car not starting, radio acting up, windows acting up, etc.).

-The cause of incorrect gear ratio codes (p0729-p0735, p1734) WITH a p0720 is because of a bad TCM. The tcm no longer sees/reads/understands some combination of output shaft speed sensor, input shaft speed sensor(s) and/or vehicle speed sensor. Because of this, it has no idea what the ratio is between the input shaft and output shaft of the transmission is (aka, the gear ratio).

-If you are getting ONLY gear ratio (p0729-p0735, p1734) codes (pretty rare from what it seems), it is most likely the valve body/solenoids and NOT the tcm. The cause of these is most likely a pressure issue within the valve body (over pressure or under pressure) channels. This can be cause by buildup in the valve body, solenoids not turning on/off/varying correctly, or, as was in my case, LOOSE/MISSING SCREWS ON THE VALVE BODY!!!

I'll leave my story under this if you feel like reading, but the short of it is:

-If you have ONLY incorrect gear ratio code(s), I highly suggest you inspect the valve body by taking it out of the car, re-torque every bolt (FSM states 70 inch/lbs), maybe disconnect/reconnect the solenoids, put it back in, do a full AT fluid change (writeups and videos on here and in the fsm) and test. If you are ok dropping the pan, you can uninstall/reinstall the valve body. There are writeups and videos on it (and in the fsm).

- If only buying a TCM or TCM/valve body assembly, get one from a vehicle that is listed as compatible on the dealers parts website. These are plug and play and will work with no flashing needed. If a listing on eBay/Amazon/whatever says it works with anything outside of that list of vehicles from the Infiniti website, DO NOT TRUST IT.

- To repeat, DO NOT BUY one of the thousands of eBay/Amazon/whatever TCM or TCM/valve body assemblies that claim it works for a multitude of Nissan/Infiniti models. You have the list of what vehicles the TCM will work with from above. You will save yourself $200 from flashing or, even worse, heartache when the TCM won't even talk to the ECU (making flashing impossible and still costing $200 for the dealer to attempt).

- If an eBay seller can't confirm what vehicle the TCM or Valve Body/TCM assembly came from (or can't even provide a VIN), don't even bother. If they can't even give you that information, then it's probably not "rebuilt" or "remanufactured" or "tested" as the listing probably claims either. I won't get into the whole hoopla about honest resellers/rebuilders, but there are enough red flags from just that missing info to avoid.

With that out of the way, let's go over what my issues (some of which I caused)were, my thought process and what I did to resolve them:

1. After reading around, ordered a "remanufactured" valve body w/tcm from eBay.

2. After more reading, the included tcm would 99% not work (first 2 digits on solenoids was 16 (indicating 2016 production) which matched the first digit of the four digit alphanumeric code under the "Hitachi" lable (was a "6")). This post helped me realize this: https://www.myg37.com/forums/engine-drivetrain-and-forced-induction/299537-code-p0705-transmission-out-speed-sensor.html#post4303811
Returned without trying.

3. After MORE reading, many people who get lucky enough with buying these claimed "works with all these Nissans/Infinitis" valve bodies/TCMs have to go to the dealership to get a flash because: a) DS/manual mode won't work or b) shifting acts weird or is different than before. The reason for this is because the tcm was pulled from whatever Nissan/Infiniti, to which either has no/differently programed DS/manual mode and/or has different gear ratios compared to what's on the g37. A flash costs $200, give or take, not worth it to me since I am already buying a used part and doing the work myself.

4. After this and trying to think of a way to guarantee myself a TCM/valve body from a similar car (you can look up your make/model/year, go to any Infiniti parts website, and see what makes/models/years your valve body/tcm works for. Should be noted, ALL brand new/used valve bodies from this list of cars will be 100% plug and play. No flashing/vinning required), I decided to just look up used transmissions for those cars and message every single one, that I felt comfortable with, asking if they would be willing to sell me ONLY the valve body/tcm assemble. I have nowhere to store a used transmission (though, would have if I could), so this was the best thing I could think of.

Finally got a bite after initially told no (many, many times), by saying I'll just play for the whole transmission but they can just send my the valve body/tcm. One I got was from a 2013 g37 coupe, 70k miles, $450. Price was fine for me, especially guaranteeing it was from a vehicle I knew I wouldn't need to flash.

The other nice thing about getting it this way is you can look up the VIN of the car it came from to see what you are dealing with interms of damage/reasons for the part out. It is 99% going to be an accident/insurance write off that was sold at auction.

5. Get the valve body/tcm assembly. Come to find out, they removed every dang screw out of the bottom (side away from the tcm) except for 3 but/bolt anchors preventing the valve body from opening. For reference, there is only 13 bolts needed to be removed to get it off the transmission. Clarified with them that they didn't actually open the valve body (would have just sent back immediately if they did).

6. Go to put it in but now have to put in ~25 extra bolts, aside from the ones to hold it to the transmission. A lot of these bolts are different sizes so best course of action is to just move them, one by one, from my old valve body to the new. Did this, installed it into the transmission. Filled it up. Went on a test drive....code.

7. Pulled code. P1734... and that's it. Nothing else. It's a 7th gear incorrect ratio. Odd part is, it went to a soft limp mode, not like I experienced with the previous issue. I could use DS/manual mode and manually shift 1st-7th without issue. Not manually shifting would work up to 7th on a restart but then lock me to 2000 rpms after a short time, which manually down shifting would fix. There was gear hunting going up hills between 5th-7th and flare on 3rd to 4th (I never had flare during shifts, not even once, since owning the car). The FSM shows that this fail-safe mode is only for when the expected and calculated gear ratios are only slightly off.

8. Thought about what to do for a few days and decided on trying my old valve body with the new to me TCM. It didn't really make much sense that the TCM or a sensor would be the issue. Bad TCM would cause other codes/issues, bad sensor would cause many more gear ratios to be out of wack. Thought it could be a bad solenoid that doesn't trip fault code for one (has to be an open or shorted circuit for that to happen) or a clogged valve body, so went with the swap route.

9. Pulled out the valve body out of the car and grabbed my old one. Looked at the old one and saw ~8 bolts under where the filter goes on. My stomach sank and my brain had flashbacks of when I did the bolt transfers the first time. Proceeded to take the filter off the valve body I took out of the car and...yup, in my tired/dumb/blind state when transferring the bolts over, I missed all of them under the filter. Now had to decide if I just move the missing bolts over or still go ahead with the swap. Decided on just moving the bolts over that I missed. Loosened all the others and tightened all the bolts to have even pressure over the valve body hooked it back into the car, test drive it and it was perfect!

10. Put about 500 miles on it, no codes, shifts well. Knock on wood, it stays that way for a little while.


Thanks for your time. It's a long read, but I wanted to lay it out for anyone who has to deal with similar issues to me.

Cheers

 

I must say, this insight is invaluable as I just recently received my first P0732 code yesterday after a 4 hour trip back home. Noticed the hard shifting for 2nd but nothing else. My hope is that it is nothing more but loose bolts on the Valve Body and if worse just getting a proper replacement. My only concern is that my G is a 5 AT model and I hope finding the valve body wont be a pain to get

Thanks!

 

The 5at has way more availability of rebuilt/remanned valve bodies from reputable dealers/manufacturers than the 7at surprisingly enough. There are also affordable upgraded valve bodies as well if you felt like spending the $.

The FSM, TM pdf (located a niccoclub I believe) will have a step by step process for removing the valve body itself as well as torque values necessary. Do not confuse ft/lbs for in/lbs in their documentation.

Would definitely do the retorquing of bolts first though if you are trying to save $. Just be sure to untorque all bolts first (aside from the screw/nut ones, can look up a picture to see what I mean) on the side opposite the TCM and then retorque them all evenly. You will have to remove the filter to expose them all.

Even in the 7at, the valve body themselves isn't the issue in finding or obtaining, it's the TCM that is a PITA lol.

A few helpful tips when going through the uninstall/installing of the valve body:

​​​- After lifting the car and before disconnecting the battery (which you really should do if you're disconnecting/reconnecting and electrical circuit on the car, in this case, the transmission plug connection), shift the car into neutral. It will make getting the valve body in 100x easier.

- Put I piece of masking tape (or whatever you have laying around) over the transmission connector (the one on the outside feeding into the transmission and connecting to the valve body) after you unplug it. You will be pushing it through the transmission while you are unbolting the valve body and most likely, your hands will be covered in fluid. Just to help prevent fluid from getting into it. If some does, no big deal, tranny fluid isn't conductive. Just clean it out as best you can.

- Look at/take a picture of the gear shift actuator (the black metal piece connected to a rod going into the valve body) with the valve body still installed. You need to have the fatter post/rod on the transmission slipped into it when reinstalling, and you can only do that while the valve body isn't bolted in.

- Follow the fsm for uninstall, making sure to label the bolts you remove by the letter given in the fsm. I used small labeled sandwich bags to keep them organized.

- With this same connector above, when you have the valve body out of the transmission, make sure it is on its correct post/tab and that the 3 other posts/tabs around it are angled/bent under the connector slightly. This will give it leverage to pop it into place when you go to reinstall the valve body.​​​​​

- Get one or two bolts somewhat threaded in (making sure the gear shift actuator is properly aligned as mentioned above), then push up on the valve body under where the connector is to get it up and through the hole it lives, holding the valve body up afterwards to get those bolts in far enough to prevent the connector from coming off the post/tab.

- Again, follow the fsm for reinstall. Main takeaway is to get all bolts finger tight while holding up the valve body, then first torque down the reamer bolt (bolt E) for alignment, then torque down going backwards (D->C->B->A) and then check them all again.​​​​​

 

Fantastic post!
Thanks for sharing it here, I’m sure it will help many for years to come.