93 Pathy Auto transmission won't shift into 2nd or fourth

[lanerjo]

Here is the deal:
93 Nissan Pathfinder 4x4 w/ Automatic Transmission

Transmission will not shift into 2nd or 4th gear. Suddenly without warning. Worked almost perfectly before (only slight harsh 1st-2nd shift)
Only fault code when checking the ATCU is Revolution sensor fault
Transmission is full of fluid (fluid is NOT burnt or discolored nor does it have shavings in the transmission fluid)
Part stores have no listing for this part.

Logic tells me it is probably more like a stuck secondary shift valve. I would think that would trip a code in the ATCU though.

Anyone else had this problem? What did you do to resolve the issue? I do not like having to use backroads to get around a major metropolitan area, I would like to be able to accelerate normally from a stoplight again as well.

[Towncivilian]

So the trans is stuck in third gear? Sounds like it's in limp mode; you can try removing the negative battery terminal for a few minutes to reset the TCM.

See AT-42 for a diagnosis procedure for the revolution speed sensor. There doesn't seem to be any aftermarket rev sensors available, and a new OEM part is $134 - so a junkyard might be your best bet if you need to replace the rev sensor.

How often have you serviced the transmission fluid? Ever did a pan drop & filter change?

[lanerjo]

The trans works in 1st and 3rd gear.
It acts like it is neutral when I manually shift it to second gear.
I will try resetting the TCM... Wouldn't unplugging the ATCU reset it just like unplugging the battery?

The transmission has been serviced regularly. I have all service records from previous owner. I will look into the new oem part as soon as I check the revolution sensor.

[Towncivilian]

I'm not sure unplugging the transmission control module would be a wise idea - it may cause other trouble codes to be thrown. I think it's safer to disconnect the battery for a few moments instead.

Does the E-AT light (if present) or O/D OFF light blink after starting the engine?

[lanerjo]

Ok after resetting the ATCU both unplugging and disconnecting the battery, and testing the Revolution Sensor circuit (581ohms) I am still having this same issue.

I have almost convinced myself it is one of the solenoids, as the one of the only things 2nd and 4th share is the Shift Solenoid "A".

The brake band controls every gear, and all circuits test fine at the ATCU, Per Mitchell's specs which are taken from the FSM.

I guess I could try and run a "cleaner" through the transmission for a few days and maybe it is a stuck solenoid due to varnish build-up.....

What are your guys' thoughts on that?

[Towncivilian]

Personally, I wouldn't like some harsh solvent in my transmission fluid. Try adding a bottle of Lubegard Red instead. Many transmission shops use it and I've had some noticeable results (reduced shift shock when overdrive engages/disengages via the "O/D OFF" button, smoother downshifts). Some OEMs even specify using Lubegard in TSBs.

[lanerjo]

My plans were to run 1/2 bottle of seafoam transmission cleaner for a week or two then change the fluid and run the other half bottle for another week or two. When and if it starts shifting into 2nd and 4th then I was going to add the lubeguard red.

Just my two cents... I don't know of anyway other than solvents to clean up what I hope is varnish. If it is the transmission then the transmission is bad anyways. Or at least that is how I see it.

[Towncivilian]

I'm not sure what exactly makes up Seafoam TransTune (which is what I assume you'll be running), but it's probably just the regular Seafoam rebadged. I haven't heard of anyone's transmission blowing up from using it, so go right ahead - it's ultimately your choice.

If you have a significant amount of varnish in the transmission, your fluid is getting too hot for extended periods of time. If things clear up, I'd install an auxiliary cooler in-line with the stock cooler as well as an in-line filter to reduce particulate wear material and extend the usable life of the transmission fluid and transmission itself of course.

If things don't clear up and you want to swap in another auto trans, get one from a 2001+ Xterra since it's the heavier duty version of the RE4R01A. It should be a direct bolt-on swap as far as I know. Or you can opt for a manual swap, it's up to you.

[fin reaper]

I am having the same issue (no 2nd or 4th). Was the Shift Solenoid A the problem - or was it something else? Thanks