My 2000 Maxima SE will downshift every once and a while from 4th to 3rd.
It will last for about 15 minutes before it upshifts again.
One odd thing that seems to happen about the same time is that the A/C stops working.
Any ideas or where to start and will a trans fluid drain and full be of any benefit?
Thanks.

 

I was reading about a similar issue that was addressed regarding the 5th gen regarding the electronically controlled engine mounts
https://en.wikipedia.org/wiki/Nissan_Maxima check out the 5th generation write up.

 

You haven't told us whether your car exhibits any codes, or whether there are any codes pending. At any rate, the following may get you going:
- Changing your transmission fluid and checking its level is a good idea. How long has it been since the last change?
- You should check for any pending codes and "incomplete monitors". This may help in the next step.
- An intermittent problem like your is most likely caused by a sensor that is about to go bad. The following sensors impact AT operation (that's why input from the above step is so important): a) AT revolution sensor (P0720), b) ATF temperature sensor (P0710), c) Throttle position sensor (TPS, P1705); and others.

Get yourself a copy of the FSM (you can get it from here http://boredmder.com/FSMs/Nissan/Maxima/), and peruse the "AT" section, and the "Trouble Diagnosis" subsections in particular.

 

As long as you use oem fluids for the tranny then its always a good idea to drain and fill it. when it happens are you lugging the motor at all?(ex. up hill in fourth with the ac on doing 40, thats like 1200rpm or less) Is your torque converter locking up at all in fourth or third? If not it may be overheating and shifting into third to cooldown. Take a look at the fluid and smell it. it should smell kinda sweet if its good otherwise if its burnt then you will smell it. Overheating fluid will burn it alot easier especialy if its old.

This sites like the doctors, the less we know the less we can help.

 

I would consider that the mounts ground all the power. If the power is grounded then it could be the issue.

 

They say to clean the ATF cooling system too.

 

OP's problem has nothing - and I mean absolutely nothing - to do with his engine mounts. Should his mounts "ground the power" (as you say), the result would be either a blown ECU, or a blown fuse, or both. So relax - and please take your concern to a more appropriate thread such as https://maxima.org/forums/5th-genera...ine-mount.html .

 

There are no codes or codes pending. The level was checked and is fine and it has been 25,000 since the last tranny change.
The last code I got was related to the cat and that was replaced and resolved.

 

The motor was not being lugged. It has happened while doing 75 mph on a flat freeway and while do moving at 40 mph in the city.
I don't know what a locking up torque converter feels like.
I'll recheck the smell and color but i remember it still having a good red tint although it wasn't bright new red looking.

 

Interesting connection maximatch12. How do these motor mounts become worn? And more importantly this sounds expensive.

 

4th gear in the city is a nono. It's an overdrive and with the ac on it has to be lugging. Also if your not giving it enough gas it will downshift automatically. At 75 you actualy need to use more power to fight the wind then at 55. If it doesn't downshift at 55 with the ac on then you may just need more throttle.

 

My wife said the A/C shut off at about the time the car downshifted...
...and the way she drives she always gives it plenty of throttle.
Its an AUTO trans so shouldn't be able to pick the proper gear given the speed, rpm and acc. running?

 

motor mounts don't have anything to do with your specific problem. you should be aware of what can happen though, especially for an 00 AT. read this article for more information.
https://drive.google.com/file/d/0B6O...psNVBqUVk/view

maximatech has been on here the past few weeks spouting a bunch of conspiracy theories trying to link random things to the motor mounts/iacv/ecm issues. you have to take everything he says with a grain of salt

 

Ok, this helps. I don't think your ATF fluid is causing the problem, but change it anyway - it's overdue for a car this old. (I am changing my ATF every 15,000 miles; I feel this is prudent for anybody who tries to keep a 16-year old Automatic Transmission going for a few years longer).

Your problem is intermittent. There are at least two possible causes:

• One/more of the sensors I mentioned in my earlier post is bad, or about to go bad. It could also be the connector or the wiring. In either case, wiggling the connectors/wires/sensors may help - the idea is to fix it or break it for good.
• An unstable electrical system can cause all kinds of problems, incl. your random downshifts. Check out your alternator and battery. When the car is running, the voltage on the battery should be about 14.5V. What is it when your random downshift happens?

If none of the above helps, I would go through the Troubleshooting Chart on pages AT-84 to AT-88 of the FSM. You may be able to answer the questions there; and only you can do the experiments required (for example, does the problem happen only with the O/D switch enabled/disabled?)

 

10-4
I'll read through the link and use extreme caution where warned. Thanks.

 

The wiggling the connectors is easy enough so that will be done. I do know the the voltage is fine when checked at idle and not moving. We'll have to monitor it if and when it happens again.

 

"plenty of throttle" can also cause the vehicle to downshift because the vehicle shifts based on pedal position and rpm. You shouldn't need much throttle in fourth on the highway. Do you often overtake people on the highway? Better yet, take note of speed vs rpm in 4th and third (ex. 35mph @ 2000rpm 2nd)

 

not for 15 mins lol

 

If the torque converter wasn't locking up then it will heat that trans like crazy. That's why I asked earlier if it was locking or not. I'm thinking that mabye it cant lockup in fourth so it shifts into third to cool down. If it can't lock up in third then that would explain why it takes 15min to "cool off". While the converter is unlocked it does make heat but it makes less heat in third that fourth becaue of the difference in gear ratio. If it locked up the trans would cool off very fast. But that's just a theory and nothing more.

 

I thought you were referring to throttle I wasn't paying attention to usernames.

This is easy to test, though. Completely let off throttle and see if it shifts back to 4th. Shut off and restart car and see if it goes into 4th. If either of those work, then it's not overheating.
Yes, he definitely needs to pay attention to rpm. That will instantly tell you whether it is locked or not.

Aren't there some TCM bugs, too, or was that just failures?


Take this for what you will, if it were my auto and the fluid is old/unknown: I'd dump a can of detergent (like seafoam transtune or equivalent) in it and drive for a few days, completely drain (from cooler line) and fill with Idemitsu type J (56.50 for 10 qts on ebay), I might drop the pan to clean it out and add Lubegard ATF protectant.

I've really been thinking about adding an inline filter (METAL NOT PLASTIC) for when I drain/fill sister's auto, so might as well do it right when doing everything else :P

 

^^^ +1 - Listen to this guy, he knows what he is talking about!

 

I appreciate the kind words, but haven't you seen my disclaimer on the engine swap thread?

 

When it has happened to me I had already been driving for and hour at highway speeds and then it downshifted for 15 minutes and upshifted after that.

 

Just talked to my wife...and she says now that the car's rpm was jumping multiple times, 3 or 4 times in her words. She pulled over and then continued on home without issue for the last three miles at a slow speed.
FYI this new info is a new add on that I was just made aware of and my original issue still exists.

 

It makes more sense as this is more normal when something is wrong.

I just checked the TSBs and they only talk about slippage on upshifts due to the solenoid valve assembly and "abnormal shifting" (slip, hard shift, no shift, improper timing) due to valve body. I only saw 1st to 2nd slippage being blamed on the TCM.
The last one is about cleaning of the oil cooler b/c debris can plug up the entrance (or so much settles in it that it contaminate fresh fluid).

 

I wouldn't recamend lube guard in this case because it has Friction modifier in it and that makes it slip worse. That ish roasted what was left of my third gear in my last auto. Seafoam transtune is some good stuff... I left it in my trans for 3k miles and let me tell you, it never felt snappier than that before. Every shift was crispier and it reduced the bad flaring I had by alot. My valve body must have been f***** up, atf was onyx colored when I got that car. Atf oil cooler being clogged would lead to this overheating and then make a few slips.

 

Well, we were assuming he doesn't have slips.

He's going to have to drive the car and catch it in the act. Women are notoriously unreliable when explaining anything, especially cars.

 

I HAVE NOT had slippage. Just the downshift. I'm leaning towards the over heat diagnosis so far. That seems to fit the symptoms so a drain and refill are in order.
Would draining from the pan work best?

 

Letting off of the gas does nothing other than drop the rpm's. As soon as acceleration is applied the rpm's rise in 3rd gear.
I did play with the O/D switch when this happens and there was no difference.

 

I was thinking that the torque converter unlocking would be easily confused with slip, not saying there is sliping but the torque converter can rise 2000rpm over the lockup rpm when it unlocks. O/d button should be for the fourth gear.

 

No, from the cooler. Take off return, put a piece of hose on it and let it pump out, then refill. Have someone shift through the gears and let it pump until fluid comes out clean. Refill, test drive, check fluid level.

Drop the pan if you want to inspect or clean off the magnet. I guess you might as well take off the other cooler hose and check for debris.