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Discussion Starter #1 (Edited)
I thought I would start this thread here to document some technical details and issues regarding the automatic transmission found in the 2005+ Nissan Frontiers, with specifically the 4.0L V6 engine.
I have learned all of this because I have been researching and troubleshooting my own transmission in my 2006 Crew Cab V6 4x4 Frontier SE with 175k miles.

Basic Information:
The automatic transmission (both 2wd and 4wd) is officially called an RE5R05A. It is a 5-speed automatic transmission. Gear ratios will vary by application. This same transmission (in slightly different forms) is used in many other Nissans/Infiniti models and other makes/models as well.
Issues:
It is safe to say that most of the issues with these transmissions (as used in the Frontiers/Xterras) can be traced back to two innocent looking hoses connected to the lower tank on the radiator. The radiator can fail and cause cross-contamination of engine coolant and ATF. This means that you will get a milky sludge in your transmission. NOT GOOD.
Many people (and the service manual) call this connection to the radiator a "trans cooler". However, I do not think that is 100% accurate. I believe the only purpose of this mechanism is to accelerate the warm-up of the ATF for better cold-start driveability. The Frontiers for sure (and probably Xterras too) already have an OEM ATF air-cooled heat exchanger located behind the grille, in front of the radiator. You can easily check your own vehicle by peering through the grill on the passenger side of the Nissan emblem.
Here is description of it from the service manual.



On my vehicle I have chosen to bypass the radiator. So all cooling is done with the air cooled one. In my climate and driving, I don’t have any need for extra cooling that could come from the ATF routing through the radiator. Your application may be different.
When I purchased the truck, the previous owner had said they just got the radiator replaced. I didn’t think much of it at the time, but it did have a shiny new radiator in it.
My Issue:
I have been experiencing SES lights on my dashboard. Scanning the OBDII port has pointed to P0850 “Park/Neutral position switch circuit” (PNP switch). I had no drivability issues, so I would just reset the code and continue on. It would be fine for a week or two, then the light would come back on. Did this for a couple months until one morning after resetting the code, the transmission went into limp mode (feels like transmission is slipping, very little power).
So I scanned it and this time had a new code P1754 “A/T overrun clutch solenoid valve circuit malfunction”. I reset this code and the truck was back to normal and has been normal ever since (about 1 week of driving, maybe 40 miles total thus far).
Basically this all points to an issue with the valve body and/or TCU.

Solution to my issue:

Researching has led me to focus on the transmission valve body (which also houses the Trans control unit TCU). It is located inside the transmission and can be accessed by removing the pan. The PNP switch is located on the valve body and so is the overrun clutch solenoid (which receives a signal from the PNP switch).
If you need to replace your valve body, it is not overly difficult. Here is a video illustrating the process.

Finding a replacement valve body can be a bit difficult because there are three different variations. You need to make sure you select the correct one that matches what is currently in your transmission. Here is a good video explaining the differences of the valve bodies.


Even though they made the video, I would NOT recommend buying from Cascade Trans Parts. Look elsewhere online, or contact your local Nissan dealer parts department. I got a quote for $1,130 for a new valve body from my Nissan Dealer (for reference).

DIVING IN:
After draining the fluid from the transmission oil pan, remove the oil pan and prepare for more drips and a mess. Let it drain and drip overnight.

Now the bottom of the valve body assembly is visible. This is where my issue became obvious. There were signs of corrosion on the screw heads and bare metal bracketry of the valve body. This is equivalent to a big neon sign saying “This transmission has experienced cross contamination!!”. My speculation is that the previous owner experienced this issue with a failed radiator and had the system flushed and put in a new radiator and called it good. ..then sold me the truck. Hope the band, and clutches and all the other internal parts are ok. I assume they are because the transmission works great except for the occasional CEL codes.
To remove the valve body, remove the bolts highlighted in the factory service manual:



With valve body out, I could see the extent of the corrosion. No wonder I was getting transmission CEL codes.


this shows the PNP switch. No wonder it was malfunctioning. So even though new fluid was flushed through the transmission after the cross contamination (previous owner), damage was already done.


So the next step was source a replacement. I found a seller on Ebay that had the correct part for my vehicle and they had excellent feedback, so I purchased from them. It is important to identify your valve carefully to make sure you are getting the EXACT correct replacement. There are several different ones out that look very similar (as noted earlier in this post).

I will follow up with another post once the new valve body arrives and installation is done.

Another thing to keep in mind is that the TCM in the new valve body may have to be programmed for your vehicle, which requires a trip to the dealer so they can do it through CONSULT. I will see how that goes and see if the truck is drivable.

Update to follow soon!
 

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Good idea and info!

I'll chime in some of my experience as well.

I had to have my trans rebuilt at 84k miles, but not due to cross contamination. Rather, I had performed the bypass at 27k miles (shortly after I bought it) and like the OP, I assumed the factory air cooler would be enough to keep things cool. WRONG!!! My trans died due to multiple fluid over temp cycles. This wiped out all the clutch material on the plates and stressed the bands. Mind you I had performed a drain and fill at the time of bypass and another at about 60k miles. I also did not tow anything during this period. I do, however, live in a warmer than average climate and frequently wheel in 100*+ temps so that is a factor. So it's not like you can blame it on poor maintenance, that little radiator cooler does help keep things cooler. Since my trans did not have cross contamination, it did not need a new valve body. For those wondering about price, the dealer wanted about $6k for a reman'ed transmission and private shops quoted between $3-5k for a full rebuild. I went with a pretty highly rated trans specialty place that I felt good about and ended up paying $2900 for a full rebuild with upgraded clutches and HD bands. Came with a 3 year 36k mile warranty too. If it had needed a valve body they said it would have been another $1100. I'm at 110k now and it still feels great.

Unsure if this was related to the heat cycles but something else that was interesting to note during the rebuild was a failed reverse solenoid snap ring. This is actually what brought me into the trans shop initially as I was losing reverse. I did some asking around on the forums about this and a few others had also mentioned this happening to them with the same diagnosis.The trans had also begun to slip pretty bad just before this.

After my rebuild, I have added a rather large (overkill) air cooler in series with the factory air cooler. I don't have a way to monitor temps but I can assume it's much cooler now. I also plan to replace the radiator and add back in the small cooler when I flush the coolant in a few thousand miles.

TL;DR:
Factory air cooler is not enough for all cases, add another cooler!
 

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Discussion Starter #3
Great info!! Yeah, I never wheel this thing and it hardly ever breaks 100 degrees. But I will definitely consider another air cooler, or upgrading the factory air cooler. I am gun shy on hooking the radiator back into the circuit, as you can probably understand. But it is a new radiator...so....maybe it would be fine:serious:
 

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Compression very nice write up clear an decisive conclusions I've come across those in my travels on youtube I'll check back for your updates. But to everyone that purchased a used one with unknown previous maintenance there are many unscrupulous shysters out there to screw anyone else with their problem Yeah I think those people saw the problem had it checked out saw the price to do it right to the tune of $6k then said hell with it tried the cheapest fastest fix they could find to get it moving an dumped it cause they were told what most were that had problem occur $$$ gimmie me more $$$ as glamisdude said "the dealer wanted about $6k for a reman'ed transmission and private shops quoted between $3-5k for a full rebuild". Or even just if you have a variation of this transmission hope everyone read this thread an watches those videos
 

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Discussion Starter #5 (Edited)
UPDATE!!

OK, so I purchased a $400 valve body off of Ebay from a seller with good feedback. Upon arrival I did a full inspection and found that it almost perfectly matched the old valve body. I suspect this is a remanufactured unit from China, based on the packaging. I checked every screw to make sure they were tight (they were) and everything was plugged in (it was) and looked OK (it did).

The only noticeable difference was the lower right corner (in the picture above) which shows a round divot in the new one, but the old one did not have this. Other than that they were identical in every way. Even the Bosch part numbers on the solenoids and TCU were the same. The new one had some test fluid that was leaking out of it, which is a good sign meaning that it was tested.

After swapping over the inlet screen and temp sensor, I installed the new one into the bottom of the transmission. Fit up was perfect.


After all bolts were torqued (70 in-lb for all 10mm head bolts) and re-checked, then re-checked again, I installed the recently cleaned oil pan and a new OEM gasket (do not use any silicone on this one!), also 70 in-lb for the pan bolts:


After everything was buttoned up, I refilled the transmission fluid with Itemitsu Matic-J ATF, available from Amazon and other places:
I ended up draining and refilling 7-1/2 quarts in the process of changing the valve body.

Since the work was completed, I have done about 50 miles of mixed driving and it runs/drives PERFECTLY! No CEL, no hard shifts, nothing. Just buttery smoothness. It even idles better, before it used to idle kind of boggy, then I would put in in Neutral and the idle would shoot up a bit. But now, it is rock solid whether it is D or N.

::smile::SO FAR SO GOOD!!! Knock on wood!::smile::

I did NOT need to have the TCU reprogrammed at the dealer. It seems to be running great and shifting perfectly, so I am not going to do this. This would be something to ask the person you buy your new valve body from.

I received (for free...I got friends::grin::) a large aftermarket transmission cooler to put behind the grille to replace the OEM one. I decided this would be a good idea considering I am no longer routing the ATF through the radiator. However, I probably wont install it for some time, winter is here and no worry of high ATF temps anytime soon.

Hopefully someone can learn from this and save themselves thousands of dollars, and just replace the valve body. It really is not that hard to do, just make sure you get a good replacement. And also be careful and follow the steps in the factory service manual, available here:
Nissan Frontier Factory Service Manuals
 

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1 Is it possible to do a re-learn on TCM
2 Is it possible to re-flash TCM with original software?
Two separate questions
 

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Discussion Starter #7
The valve body/TCU I got did not need a reprogram. It worked great out of the box.
The ONLY place that can reprogram a TCU is your Nissan dealer. I called several independent transmission shops and they all told me that.
 

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Thank you for the very detailed and thorough post. I appreciate all the pictures you included with your explanations of the work involved as well.

Sub'd for future use in repair (if necessary). Hopefully I will not have to attempt this repair since I have a 2015 with the redesigned radiator.
 

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Really good info!

Sorry if I missed this somewhere (I searched!). I understand the ATF/coolant mixing issue is pretty much a non-issue with 2010+ Frontiers and as mentioned above, 2015+ have a redesigned radiator. What is different with the 2015+ in terms of the radiator and ATF cooling?

Reason I ask is we have a 2017.
 

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Discussion Starter #10
I have no idea about any changes that may have happened with later model years.

UPDATE:
Here we are about 6 months later. Transmission is still working absolutely perfectly. No complaints, no issues.
This was a good repair and money well spent.
 

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Nice compression glad to hear an know yours is doing well
 

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Good idea and info!

I'll chime in some of my experience as well.

I had to have my trans rebuilt at 84k miles, but not due to cross contamination. Rather, I had performed the bypass at 27k miles (shortly after I bought it) and like the OP, I assumed the factory air cooler would be enough to keep things cool. WRONG!!! My trans died due to multiple fluid over temp cycles. This wiped out all the clutch material on the plates and stressed the bands. Mind you I had performed a drain and fill at the time of bypass and another at about 60k miles. I also did not tow anything during this period. I do, however, live in a warmer than average climate and frequently wheel in 100*+ temps so that is a factor. So it's not like you can blame it on poor maintenance, that little radiator cooler does help keep things cooler. Since my trans did not have cross contamination, it did not need a new valve body. For those wondering about price, the dealer wanted about $6k for a reman'ed transmission and private shops quoted between $3-5k for a full rebuild. I went with a pretty highly rated trans specialty place that I felt good about and ended up paying $2900 for a full rebuild with upgraded clutches and HD bands. Came with a 3 year 36k mile warranty too. If it had needed a valve body they said it would have been another $1100. I'm at 110k now and it still feels great.

Unsure if this was related to the heat cycles but something else that was interesting to note during the rebuild was a failed reverse solenoid snap ring. This is actually what brought me into the trans shop initially as I was losing reverse. I did some asking around on the forums about this and a few others had also mentioned this happening to them with the same diagnosis.The trans had also begun to slip pretty bad just before this.

After my rebuild, I have added a rather large (overkill) air cooler in series with the factory air cooler. I don't have a way to monitor temps but I can assume it's much cooler now. I also plan to replace the radiator and add back in the small cooler when I flush the coolant in a few thousand miles.

TL;DR:
Factory air cooler is not enough for all cases, add another cooler!
Hey glamisdude, I am about to be in this boat as well. Can I ask why you chose to upgrade the clutch and HD bands (and what are those?)?

If I have to get the transmission rebuilt, I want this truck to run a long damn time and am looking at what else I should have done without shelling out a whole lot more cash.

Thanks!
 

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No heavy duty bands I know of and of the 6 (?) clutch packs I measured only two needed new frictions. The steels were all good. No heavy duty steels or frictions that I know of. It is important to buy the correct “selective” retaining plate to give the reverse clutch pack the correct clearance. Also replace the flimsy OEM snap ring for reverse with a heavy duty one that will not pop out like the original.
 

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I have no idea about any changes that may have happened with later model years.

UPDATE:
Here we are about 6 months later. Transmission is still working absolutely perfectly. No complaints, no issues.
This was a good repair and money well spent.
Hey compression! Bumped into your post, it was very helpful. (I can see the pictures too!) But I do have questions for you.
Could you please share the link from where you ordered the valve-body? I have a G35 2005(120k miles) with the same RE5R05A transmission.
I got a P1769 code, which means perhaps HLRC soleniod failed. I replaced only that soleniod (with new MATIC S), and it ran great for a week till it started throwing code P1764 . That mean Direct Clutch Solenoid Valve failed, which I checked was functioning fine (9ohm) while replacing the HLRC soleniod.
I got a set those soleniod from ebay. I have a feeling some other soleniod may once I replace the old ones. Any advice?
 

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Really good info!

Sorry if I missed this somewhere (I searched!). I understand the ATF/coolant mixing issue is pretty much a non-issue with 2010+ Frontiers and as mentioned above, 2015+ have a redesigned radiator. What is different with the 2015+ in terms of the radiator and ATF cooling?

Reason I ask is we have a 2017.
FYI, I thought the issue was fixed after 2010 also until 2 weeks ago, and now my 2013 Pro 4X, 70k miles, is in the shop getting the tranny rebuilt, new valve body, radiator bypass etc due to cross contamination. They said they've fixed hundreds of these, but mine is the newest.
 
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