My 1998 Pathfinder 163,000 miles started to delay shift into 4th/overdrive. Fuid is full and clean. O/D switch doesn't do anything to help it upshift, and it seems to work fine (light comes on when switched).

I can get it to shift into 4th by slightly letting off accelerator and then it goes into 4th and stays there with steady speeds over about 50mph.

No codes on for transmission. Any ideas where to start looking for problem cause? Thanks!

The transmission Nissan used was the JATCO RE401A and In most cases it's due to the TCC lockup solenoid failure. You can test it by removing it from the valve body assembly and applying 12V in order to hear the "click" of engagement. Given your mileage it may be wise to replace the entire solenoid pack because the effort involved is the same if you replace just one or all four. Going a step further you may find it smarter in the long run to replace the entire valve body assembly because you can get the solenoid pack for around $200 but the entire rebuilt VB assembly can be found for less than $400. A competent transmission specialist should be able to replace the VB assembly in about one hour. For the home mechanic, it's kind of messy because you need to pull the transmission pan of course and work directly under it on your back while it's dripping fluid in your face. This is the type of job best handled while the vehicle is fully off the ground.

Thanks. Do these throw codes on oBD2, or are any more codes readable by special tranny reader or by special process I can do?

There is a code - P0744 for TCC lockup failure that an OBD2 reader will see, but you can also have a failure without the code being triggered. Wiring harness issues could be involved. What I'm puzzled by is that you said the O/D switch works and will activate the light. How many miles ago was the last fluid change?

I'm not sure. It looks fresh. The motor has been removed once, and the tranny disconnected twice for that swap and before that reworking all the bearings, so fresh top-off was put in then also, by mechanic. Unless he caught and reused it. But looks like new and pink and dipstick has no residue on it either.

I wonder if the mechanic put noncompatable fluid in it. I'll ask him what he used.

Yeah I can turn the O/D off while it's stuck in 3rd, the light comes on showing that but nothing changes. Then when I turn the O/D back on it won't change to 4th unless I ease up on the pedal a little.

I guess I should drop pan and see what i see and change filter, if there is one. What fluid do they do good with, if ya know.

I have RE401A , spec for Nissan-D , had 8 changes in 24 years , twice in a row I tried Castrol Japanese car formula =OK , another time , twice in a row with Valvoline MAX Life = OK ; Nissan -D supposed to be a Dexron III type .
Nothing was ANY better/superior than REAL Nissan-D in my 93 J30 ! The tranny tho WAS NOT PROBLEMATIC
Others will have stories on what they experienced too now - ask around , see who else's opinions on here of course.

So the after market fluids both just as bad? What did it cause?

Coyote ......quick response , must be for me , I don't see anyone else - you talkin to me

Seriously , what I say 10 min ago shouldn't necessarily imply ANY problem ......I even mention my RE401A was never problematic , probly because of very frequent care and if you maybe misconstrued that line or maybe your trying to gather IF ANY of those fluids , in my case , have had any observable negative effects , and no they did not , we're just responding to "what fluids does it call for " - that's all folks.
The specific " what do they do good with "........MY opinion Nissan-D from Dealer , yes.

Just looked at maint record and ONE time put Mob1 Synth trans fluid , because high heat capability - but NO observable benefit nor better driveability noted. Now some DO like the Mob1.

p.s Most transmission shops ,the Dealer , transmission manuals etc WILL say " refill with exact / specific factory fluid for diagnostic purposes " you observe performance with WHAT'S SUPPOSED TO BE IN THERE (Nissan-D) . And later IF all is well is when you MAY experiment with other "stuff " !

"Yeah I can turn the O/D off while it's stuck in 3rd, the light comes on showing that but nothing changes. Then when I turn the O/D back on it won't change to 4th unless I ease up on the pedal a little."

So if it is upshifting then it would appear your TCC solenoid is working. Mac makes a good point about fluid. If you don't know when the trans fluid was changed or what exactly was used then you should always drain and refill and start a new baseline. One last question - is your engine idle at the correct setting - 750rpm when warmed up?

I checked fluid again today on completely level ground, in P and N (they read the same). After a long idle, some revving, some light 4x4 modes on my hills. It was full hot temp. It was about 20 ounces low. I put in 23, just a little extra. It was at the cold/hot divide line on the stick, so not very low, or off the stick. I topped it off and will check to see if any difference tomorrow on the hardtop higher speeds. I doubt it as 20oz isn't probably enough to cause any issues.

And after new , good fluid IS drain & filled or pan-dropped , and STILL wonky , and you need to "get back into v-body"..?.....THAT"S THE time you MAY go recapture and SAVE the good fluid to re-use , so you don't really waste $$$$$