2004 SE 4WD Automatic Transmission Swap Options

[agentorca1]

Hey there, sorry if this is in the wrong place, I'm new. I just bought a 2004 pathfinder off FB marketplace, and I love it to death. Small issue, the transmission feels like it's going out (really hard shifts in and out of second gear, limp mode (this has not happened since I swapped the filter out), overdrive gear not engaging despite overdrive being on, etc). I did swap the radiator and transmission filter with a fluid swap (NOT a flush, I know that's really bad for old trannies) in case it was the strawberry milkshake of death issue, and it didn't fix it. I wanted to initially do a manual swap, but that's not really in my budget or skill level unfortunately. I was wondering what options you can do for an auto trannie swap without too much trouble? I would prefer at least 5 gears, (the 4 speed currently in it makes the engine feel really sluggish compared to what I know it can do) but are there any out there you can bolt in and run without issue? Any help would be much appreciated, I taught myself everything I know about mechanic stuff so I don't know all of the complex things yet unfortunately.

[agentorca1]

The biggest concern I have is keeping the original towing capacity. (I think about 5 thousand pounds from what I remember?) I plan to use this thing to tow my 350z around to autocrosses, so that is really important to me. If it somehow goes higher from a better transmission, great. Lower is a no go though.

[Slartibartfast]

SMOD was an R51 thing, shouldn't be an issue on the R50. It sounds like the valve body may be acting up, but I'm not an auto trans doctor. Any codes? The AT section of the service manual (free download from Nicoclub) might help track down what you're up against. 

 

Closest to a bolt-in that I'm aware of is the manual swap. Lock recently did a write-up about all that goes into that. I haven't heard of anyone swapping in a later auto trans. 

[agentorca1]

18 hours ago, Slartibartfast said:

SMOD was an R51 thing, shouldn't be an issue on the R50. It sounds like the valve body may be acting up, but I'm not an auto trans doctor. Any codes? The AT section of the service manual (free download from Nicoclub) might help track down what you're up against. 

 

Closest to a bolt-in that I'm aware of is the manual swap. Lock recently did a write-up about all that goes into that. I haven't heard of anyone swapping in a later auto trans. 

I thought so too on the SMOD but there was mixing in the fluids so idk what happened there. The previous owner also tried to pull a fast one and swap the fluids before selling it to hide the issue from me (why is it so hard to be honest? I would still have bought the car because I know how to fix the issue lol). Upon further research, I have a feeling there's a shift solenoid or two that have gone out. It's at the mechanic right now and they're taking a peek. Normally I would try and mess with it but I'm working 7 12 hour shifts rn so I really don't have time unfortunately. There's a few cat codes and the fuel level doesnt work, which also has a code. There's one code that's thrown me off. P2135. Throttle position sensor A/B Voltage correlation. I swapped the throttle body and the code came back after about 170 miles, which tells me it's more intermittent than anything. This code puts it into limp mode. There's a few things it could be. I didn't go with oem for the throttle body, and I know Nissans get really mad when you do that to them. It could also be a wiring connector issue, or it could be something with the transmission. I've heard that transmission issues can throw throttle body codes. There's no transmission codes that I saw on my code reader, but I don't have a fancy shop grade one so what do I know. The car does have the manual still which is nice. I used it to find the correct transmission fluid for the swap, as well as the fluid amount.