Is the "transmission line pressure solenoid valve" the same as a "automatic transmission control solenoid"? I am having an issue shifting into "D" when the transmission is cold with my 1999 Infiniti Q45 and am planning to swap out this valve that was discussed on another NICO forum post titled "Transmission will not go in "D" when cold". I can find the "automatic transmission control solenoid" online but, talking to a few people this doesn't seem to be the same as the "transmission line pressure solenoid valve". However, I'm really not sure. A link to the part would be great if anyone knows which one it is.

There's no single solenoid that controls the whole tranny, there are a group of them incorporated into the Valve Body assembly. Nissan generally calls the VB assembly a "Control Valve". There are four solenoids on the top side of the VB, three in a group and another one off by itself. The one off by itself is the Line Pressure Solenoid. See page AT-222 here:
https://www.nicoclub.com/service-manual ... 9%2Fat.pdf

From what I see in the parts drawings, you need to buy all four together in a kit, p/n 31940-41X09 or 31940-41X13 (supersedes).

VStar650CL wrote: ↑

Tue Jun 06, 2023 12:38 pm

There's no single solenoid that controls the whole tranny, there are a group of them incorporated into the Valve Body assembly. Nissan generally calls the VB assembly a "Control Valve". There are four solenoids on the top side of the VB, three in a group and another one off by itself. The one off by itself is the Line Pressure Solenoid. See page AT-222 here:
https://www.nicoclub.com/service-manual ... 9%2Fat.pdf

From what I see in the parts drawings, you need to buy all four together in a kit, p/n 31940-41X09 or 31940-41X13 (supersedes).

Thanks for the quick reply. Looking at the repair manual, it appears that these 4 solenoids you referenced are near the upper valve body whereas the "torque converter clutch solenoid valve" is in the lower body. I'm assuming the lower valve body is what you see when you drop the transmission pan, and that I will have to drop the upper and lower valve bodies to reach these 4 solenoids?

That should be correct.

VStar650CL wrote: ↑

Tue Jun 06, 2023 2:52 pm

That should be correct.

Okay, thanks. Any special considerations when doing this? It appears that once you unbolt the "torque converter clutch solenoid valve" from the lower valve body, you can then unbolt the entire valve body (both upper and lower including the seperator plate) in one piece. Then I can unbolt the 4 solenoids I am wanting to change from upper valve body?

I haven't done one myself (I'm a Nissan tech, not Infiniti), but according to the FSM you shouldn't need to split the VB, just drop it. There are 18 screws holding the whole thing up. See AT-196.

Okay, excellent, thanks. I could probably pull this off. I do see a warning that says "Be careful not to drop manual valve out of valve body". What exactly is this, where is it located, and how do I avoid dropping it?

It's a shuttle valve connected to the shift mechanism that tells it which gear to be in. Once the VB is out, it can slide out of the hole and hit the floor. It's very precisely machined, so fumbling it can be expensive.

VStar650CL wrote: ↑

Wed Jun 07, 2023 9:41 am

It's a shuttle valve connected to the shift mechanism that tells it which gear to be in. Once the VB is out, it can slide out of the hole and hit the floor. It's very precisely machined, so fumbling it can be expensive.

Okay, I see, thanks for the warning. Does it slide out from the top of the valve body or somewhere on the side? I was trying to get a reference of where exactly it is located in the AT Manual but, I don't see a visual reference to it.

It will be horizontal. It's usually a 4~6" long shaft that goes deep into the VB, but it's only held in position by the cam on the shift shaft which moves it in and out. Once you separate the VB from the trans case, it's just floating in the hole with nothing to hold it in if you tilt the VB the wrong way.

VStar650CL wrote: ↑

Thu Jun 08, 2023 5:51 am

It will be horizontal. It's usually a 4~6" long shaft that goes deep into the VB, but it's only held in position by the cam on the shift shaft which moves it in and out. Once you separate the VB from the trans case, it's just floating in the hole with nothing to hold it in if you tilt the VB the wrong way.

Okay, thanks for the information. Which page of the AT manual did you find the part numbers on. I have searched through it a few times unable to find them?

Not sure what you mean, they don't give part numbers in the FSM. InfinitiPartsDeal has OE parts diagrams, just feed it your VIN.

VStar650CL wrote: ↑

Thu Jun 08, 2023 2:04 pm

Not sure what you mean, they don't give part numbers in the FSM. InfinitiPartsDeal has OE parts diagrams, just feed it your VIN.

VStar650CL wrote: ↑

Tue Jun 06, 2023 12:38 pm

From what I see in the parts drawings, you need to buy all four together in a kit, p/n 31940-41X09 or 31940-41X13 (supersedes).

Ah, okay, I can definitely do that, thanks. I was just wondering how you found the part number for the 4 solenoids along with the superceded number?

InfinitiPartsDeal. I like them (and NissanPartsDeal) because they have OE parts drawings and the OE database, so if you plug in your VIN you'll pretty much always get the right part. I work at a dealership, but they're faster (and sometimes more reliable) than the parts counter guys when combing for oddball stuff that I don't know the right name for. Parts naming is a long-running complaint with Nissan, probably 75% of all parts are called one thing in the FSM and a different name in the parts database. Being able to simply comb the drawings myself can be very helpful.

Okay, thanks a lot! I am going to order the solenoids today and plan to replace them in a week or two. I will post how it turns out.

VStar650CL wrote: ↑

Tue Jun 06, 2023 12:38 pm

There's no single solenoid that controls the whole tranny, there are a group of them incorporated into the Valve Body assembly. Nissan generally calls the VB assembly a "Control Valve". There are four solenoids on the top side of the VB, three in a group and another one off by itself. The one off by itself is the Line Pressure Solenoid. See page AT-222 here:
https://www.nicoclub.com/service-manual ... 9%2Fat.pdf

From what I see in the parts drawings, you need to buy all four together in a kit, p/n 31940-41X09 or 31940-41X13 (supersedes).

I was looking at the torque specs on page AT-222. I see that most of the bolts I will touching on the valve body have a torque spec of 7-9 in-lb, is that correct? I have a torque wrench that has in-lb increments and I plan on torquing everything according to the manual. I have used in-lbs before when torquing, but converting this to ft-lb that I'm more familiar I am getting 0.58 - 0.75 ft-lb. Just seems really like a really low torque.

No, you're reading that incorrectly. It's 7~9 NM. Look in the lower left, the figures in that diagram are NM (Kg/M, lbs/in). So its 51~78 lbs/in.

VStar650CL wrote: ↑

Mon Jun 12, 2023 6:40 am

No, you're reading that incorrectly. It's 7~9 NM. Look in the lower left, the figures in that diagram are NM (Kg/M, lbs/in). So its 51~78 lbs/in.

Ah, I see now, thanks. The solenoids came in yesterday. I'm going to shoot for this weekend to swap them out.

just catching up on this.
VStar has you covered, will be self-evident, but look for connectors inside the case/pan that need to be disconnected to drop the VB. also suggest using a piece of cardboard that you can put the bolts thru in the same orientation as you take them out (they are different lengths). Replace the metal strainer and clean the magnets.
But looking back to your original problem statement, it's not obvious to me that the solenoids are the root cause. Could be--but not certain. What other maintenance and history can you provide?

3Q Jay wrote: ↑

Tue Jun 13, 2023 1:10 pm

just catching up on this.
VStar has you covered, will be self-evident, but look for connectors inside the case/pan that need to be disconnected to drop the VB. also suggest using a piece of cardboard that you can put the bolts thru in the same orientation as you take them out (they are different lengths). Replace the metal strainer and clean the magnets.
But looking back to your original problem statement, it's not obvious to me that the solenoids are the root cause. Could be--but not certain. What other maintenance and history can you provide?

Hey Jay, thanks for commenting. I do have a plan for ensuring the bolts are tracked back to their location when removing them from the VB. Thanks for stressing this. The car has had a long history of "morning sickness" if we want to call it that in this case (maybe the last 5-7 years). The car has never wanted to shift into "D" when its cold but, would do so after it idles to warm up for a while, or was able to be started off in "1" or "2". The problem has gotten worse over the years so that even in the summer months after idling to warm up the car will have to be first shifted in "1" and driven, shifted in "2" and driven and finally into "D" after a few miles. Since "1" and "2" are the same gears as "1" and "2" in "D", I always assumed this had to be some type of electrical issue. I do admit changing these solenoids is a long shot though. A few years ago I dropped the pan, replaced the filter, flushed the transmission and filled it back up with factory Nissan Matic ATF. This did nothing. I am open to any suggestions. Let me know if you would like any additional information. I do have some codes written down at how that were picked up from a code reader quite a few years back. I will grab them as well this evening.

thanks for the update. glad to hear strainer previously replaced. I think I hear that it stays in neutral when the selector is moved from "N" to "D"? For clarity-are you saying it doesn't *upshift* out of first when cold and the selector is in "D"? Does "R' engage quickly when shifting from P to R or N to R?

That is correct regarding the first part, thanks for the reply. It will stay in neutral when the car is cranked and shifted from "P" to "D". It will not shift into "D" at all until the car has been driven first with "1" or "2" selected on the gear shift. Usually once this procedure has taken place, the car can be left in "D" for the remainder of the trip. Although, sometimes, if the car comes to a stop, say a stop sign or red light, shortly after this manual shifting procedure, it will again have to be shifted from "1" to "2" and then "D" again. If the car is sort of warmed up, but not all the way, you can start driving with "2" selected and then shift to "D" after a little while. If things are cold, it will have to first be started off in "1" and driven for a little while before even shifting to "2", and then driven a little while longer before shifting into "D". it will stay in neutral when "D" or even "2" is selected when its cold. Reverse always works fine, cold or hot. Let me know if that makes sense or you would like any more information.

Did you attempt to pull transmission trouble codes to diagnose the problem?

Ryantzer wrote: ↑

Wed Jun 14, 2023 12:26 pm

Did you attempt to pull transmission trouble codes to diagnose the problem?

Hey Ryantzer, thanks for posting. I do have some codes that were pulled off of the car from years back. Let me grab those and see if any are potentially related to the issue. If not I can have a code check run on it and I'll post the findings here. Would this be done at your local auto parts store? I believe my local auto parts store will do a free code check.

Codes from years ago won’t be relevant today.

Your local auto parts store is probably not going to have the ability to pull anything more than basic OBD2 codes with their code readers. It will likely take a more advanced scanner, or there may be procedures in your factory service manual to pull codes without using a scanner. Once you’ve got codes the FSM will also have the diagnostic procedures to follow for them.

Ryantzer wrote: ↑

Thu Jun 15, 2023 5:35 am

Codes from years ago won’t be relevant today.

Your local auto parts store is probably not going to have the ability to pull anything more than basic OBD2 codes with their code readers. It will likely take a more advanced scanner, or there may be procedures in your factory service manual to pull codes without using a scanner. Once you’ve got codes the FSM will also have the diagnostic procedures to follow for them.

Okay, I will do some research and post what I find. I did have a diagnostic check at an Infiniti dealer about a year ago and they reported "DTC P1492 STORED FOR THE PURGE CONTROL VALVE SOLENOID". I don't see that code in the transmission repair manual. Appears that it might be related to the evaporator.

Locate a copy of the Nissan factory service manual - if you're planning on doing any work on your vehicle it's the best source of diagnostic and repair info. I think I found mine on Q45.org, but some capable Google-fu should turn up a downloadable version if yours isn't there.

Ryantzer wrote: ↑

Thu Jun 15, 2023 6:26 am

Locate a copy of the Nissan factory service manual - if you're planning on doing any work on your vehicle it's the best source of diagnostic and repair info. I think I found mine on Q45.org, but some capable Google-fu should turn up a downloadable version if yours isn't there.

I have a copy of the owner's manual in the car. I downloaded another copy (link below). I don't see a way to self check codes. All I can find is where it says that the ECM stores codes for reference by a technician.

https://www.infiniti-techinfo.com/refgh ... ti-Q45.pdf

@Ryantzer is talking about the service manual (FSM), not the owner's manual (OM). The FSM is the document I linked for you earlier. The linked section is the for the transmission, but the other sections are available here too:
https://www.nicoclub.com/infiniti-service-manuals

Ryantzer wrote: ↑

Thu Jun 15, 2023 6:26 am

Locate a copy of the Nissan factory service manual - if you're planning on doing any work on your vehicle it's the best source of diagnostic and repair info. I think I found mine on Q45.org, but some capable Google-fu should turn up a downloadable version if yours isn't there.

Okay, I see some of the self diagnostic procedures in the transmission service manual now. It sounds like the TCM codes are overlapped with the OBD-II and stored there as well. I will check the codes and run through the self-diagnostics and post back what I find.