This has been happening persistently for a few months now, and I can't for the life of me figure out what is going on.

Background: 2000 GXE, automatic transmission

When driving for extended periods of time at 'higher' speeds (~45+ minutes constantly at 70/+ mph), my transmission will randomly downshift from 4th to 3rd. I'd literally be cruising down a highway (either with cruise control or normal gas pedal) and it will downshift once, as if I just floored it to overtake someone. There is nothing that sets it off, it just happens. It will not upshift back into 4th either. The only thing that brings the shifting back to normal is if the car sits for a while - 'cools down' in a sense for an hour or two. Sometimes it needs longer than that.

What I've tried:

-Thinking it was a tranny fluid overheating issue, I added fluid. No dice.
-It is not the TCM, I tried a different TCM (that newer TCM is up for sale in the 5th gen classifieds) with the same results.

I haven't taken it to my mechanic just yet, still trying to gather information. It doesn't affect me very often because my daily commute is ~40 minutes, only 15 minutes of which are at 60mph or so. But it's a nuisance if I have to drive anywhere of distance.

Your thoughts?

 

sorry to hear you're still having this issue man..good luck. its a real screwy thing to be happening

 

Thanks man. Happened about 5 miles before I got to the meet a couple weeks ago lol.

 

Maybe it has something to do with your overdrive feature.. maybe thats acting up, because thats what happens then im on the freeway and i turn off the OD..

 

Thanks for the suggestion. A buddy of mine mentioned that same thing - perhaps something electrical with OD. My OD button works fine when this issue does not occur.

The thing that's really getting to me is - why only after extended driving?

 

Does the O/D OFF come up on your dash when it happens?

 

again, check ATF

 

Nosir, it does not.

Will do...

 

even if it was to do with your OD button shorting out, it would OD/OFF whenever it would take itself out of OD....

Whenever your on the highway and it shifts out, does the car accelerate by itself? if it does, probably your cruise control is eff'd..

could be brakes sticking.. holding the car back.. thus making a tougher load to carry.. ect lots of things could make it come outta OD.. :|

 

Right...which is why I don't think it's OD.

Nope...

Highly highly doubt it. Brakes work fine, none of the 4 calipers are seized/stuck.

 

it mayt be something electrical to think about..a friend of mine had a similar issue and it ended being something in the CPU

 

Thanks for the suggestion. Do you mean ECU? I haven't had any other troubles with my ECU except for a pesky P0430 code I've had for a short while. I swapped out the TCM, same results.

On a side note, I checked my tranny fluid - all red & at the correct level. I do a full flush (with machine) every 30k on the dot.

 

Your tranny is going, happened to me as well. Its popping out of over drive, thats one of the first symptoms. Does your tranny spike at all?

 

Define 'spike'

What other symptoms did you experience and how are you so sure the transmission is 'going'

 

I'll be honest I don't know what exactly spiking is but I can detect it and I do know it means your tranny is basically toast.

What you need to look for is inbetweeen shifts if theres any rise in rpms during the shift.

 

eh.. mine does that from 1st to 2nd.. and yesterday it was pretty hot outside.. like 100F outside.. and i had a hard shift from 1st to 2nd ...

 

How many RPM does it jump when going from 4 - 3? It may just be the lock-up TC.

 

I'd love to know what's going on. I know when its hot out side, my transmisson slips and the rpms rev between 3-4k. When it cools, its fine! Does this mean my tranny is going also? I never really associated the revving with the transmission, I thought the revving would be an engine issue.

 

eh.. mines not that bad.. its only sometimes it does it though.. it goes like 1st to 2nd.. and the RPMs go up by like 200-300rpm .. then it shifts.. too smooth imo lol

 

If the engine is revving and the car isn't moving while in gear, then I would blame what's in between the engine and the drive wheels.

My A32 is the same way in that now it never ever gets into OD (4th). And from 1 -2 it hangs longer than it should.

My A33B used to hang on in between 1 & 2, but that changed for the better after I replaced the VB.

 

Nope, shifts are fairly tight. Sometimes when it's extremely cold I have to go easy on the accelerator for the 1-2 shift.

See above

It's the proper RPM for being in 3rd, literally a downshift. Depends on the speed of course, but I don't recall an actual #. It seems proper though, if that makes sense.

I was thinking about this, but I'd like to diagnose the problem first before I spend on a mod that might not fix an already-existing issue.

 

A hard shift may not denote a tranny issue, that could be your mounts instead.

Any slipping is a really bad sign. Odds are it will last for some time but in reality it could go today it could go in a few years.

Thats bad.

 

it doesn't happen all the time though. i get a squeek. imo thats bad.. lol

 

The only difference from 3rd to 4th (OD), is the lock up TC 'action'. So, it should only be a few hundred RPM.

 

I guess I should only drive on cooler days when there's no traffic, that way it will last longer, does anyone know what trannies run?

 

yeah.. like 3k for a rebuild/brand new one from nissan

bout 1.5-2.2k for a 5speed from nissan + random 5speed swap materials = around 3k

:x

 

Sounds about right, but I can't confirm until it happens again. Doesn't happen often because my daily commute is not long enough to make it occur.

 

That &, depending on the distance/time/nature of your commute, the lock up TC (what some may refer to as the 4th gear shift) wont occur after the tranny has reached operating temperature, which is longer than it takes for the engine to reach said temperature .. so it does take a while.

 

Interesting. My daily commute is about 32 miles/ 45-50 minutes. Only the last stretch of it (10-12 miles) is the only section that is constant higher speeds - about 60-65. The rest is between 30-60 mph with stops & lights.

So it seems you're right, my commute does not get the tranny hot enough. But with an extended distance that causes the 'heat' and consequently the issue, what exactly do you think is making it downshift as it does?

 

Wow ... that commute should do it.

 

It doesn't, which is the strange thing. But it persistently happens on longer drives: 30 minutes or more at 60-65mph or more.

 

32 miles is more than enough miles for your trans to come to operating temperature and get the TC locking. I get out of my sub division... drop off my wife 3 miles away driving in school zone not going over 35-40 and then hit 95... TC locks up instantly at 43mph... 01 GLE-auto here with 178K ... driving between 70 and 80... she wont come out of the TC unless really stepping on her.... If you are randomly noticing the trans drop out of TC and go back there is something going on...
Let me ask you this... do you have many inclines during your commute? if so then yes the trans would exhibit what you are saying. If it happens on flat roads... then its a problem.

 

Mine does too, at about the same speed.

Reading >> you. It randomly comes out when cruising after extended periods of time, but DOES NOT GO BACK IN until I stop the car and let it 'cool'

Nope, all flat. Yes, a 'downshift' to 3rd so to speak when going up an incline, I'm aware of that.

It does, hence the reason for my thread.

 

How close are you to your next complete fluid exchange?

Get 3 qts of Dex/Mer III and do a drain and fill. I wud def try that to see if it alleviates the issue.

Something is definately going on in the trans once it is heating up. Hv you cleaned up the fins of of your radiator recently to make sure it is getting enough cooling?

 

I get a full flush (done by a machine) done every 30k miles. Last time I did it was at 90k, and I'm currently at 125k. I haven't gotten it done yet because of exactly this issue. If I can figure out what the issue is, then the flush can be done at the same time as the transmission servicing.

Fluid levels are fine, and my radiator is new as of 5k miles ago. Problem persists.

 

You need new fluid and you should be fine. Just try the 3 qt drain n fill and you will already notice a difference. you can get a gallon of pennzoil dex III for like $10 at pepboys.... I wud def drain and fill at the mileage you are at. Also, my suggestion to you would be to continue with drain and fill every 7-9K miles rather than doing a machine flush. I hv been doing this for the last 80K miles and not even using syn fluid just the reg. dex/merc III.

 

I'll give it a shot.

Any other suggestions? I still haven't been able to figure out exactly what the issue is, just possible remedies.

 

its rediculous though.. theres alot of... i changed my atf and it started slipping a couple of months later.. horror stories.. :P

 

Realized I never updated this thread with the outcome. Though a machine flush was done every 30k, the screen/filter was never cleaned nor replaced. I had my rear main seal replaced a few months back and asked my mechanic to look into the issue at the same time. From the moment I described it, he was certain it was a clogged screen. He changed it at the time of the rear main seal job - and the problem was resolved.

Long story short, the clogged screen/filter was not allowing for proper cooling.

When the temperature got hot enough, it downshifted as described above.

And just to add his opinion and methodology - Nissan transmissions require Nissan fluid, he swears by it.

 

My car has done the down shift from 4-3 thing a couple of times. I know for a fact that it needs a rebuild 172K+ on a stock FWD trans is a lot, but I'll give this a try and go for a nice long drive and see what happens.