you say 'drop back down to 4th or 5th' - there is no place to come down from if your in 5th. When going downhill at 50-60 or when coasting even uphill, a tranny is not going to drop into a lower gear. A quick jolt will do nothing but confuse a tranny - OD off will make it shift out of 5th(or OD) and into 4th and not allow 5th until you turn it back on. (5th is OD)

Hill descent does not operate at highway speeds and think maybe only in 4x4 or 4L, but can't remember as I've only used it once. Check it out in owners manual.

 

This could have been a number of things, but as far as it being hill ascent/descent control, it was not. That would strictly control the brakes, holds them for 2 seconds after you take your foot off the brake in the ascent mode, and maintains engine/vehicle speed with the brake in descent mode.

If this has happened more than once, have variables been similar? Same - down hill pass, to uphill slow down? If so, I personally wouldn't worry about it. It could be the vehicle control system holding the transmission in the low gear since you got on the brakes before it had a chance to upshift. This could cause a forward jolt since you'd be losing engine braking going into a higher gear (3rd to 4th or OD).

 

If you are driving it hard or manually shifting into 3rd to keep RPMs up, the transmission will hold gears longer even after you shift back to drive. This has happened to me before as well. I think the tranny thinks you want to drive hard so it holds gears longer so you can do that.

 

Good question, but VDC (Vehicle Dynamic Control), not Hill Assist, may be the culprit.
I don't have VDC but wish I had, so I'm curious about this.

 

Thanx for the replies. Sorry if it was confusing by saying "dropped down". What I mean by that is that there is no additonal need for power so it changes (upshifts) to a higher gear from 3rd to 4th to 5th. And I don't really drive it hard, just the occasional 5,000 rpm pass.

And I must have used the wrong term, but some vehicles have a computer program that keeps a vehicle in a lower gear when it senses it going down a grade and uses engine braking. Not sure if that is what Nissan's Hill Descent is or not.

I'm not overly concerned yet since I didn't hear any unusual noises/clunks and it seems like maybe it was just me making it worse by switching OD/Off and then gasing it.

 

When you say hard downshift too me it sounds like what you did was manually drop the gear selector from 'D' to '3'. But I know you would have realized that was the issue.

I catch my automatic doing weird things every now and then too. Not completely the same but if I'm travelling down a steep grade, like on my way back from Tahoe, and it's steep enough that I don't need to touch the accelerator, and even while coasting I'm still catching up to the vehicles in front of me so I have to feather the brake a little, the transmission will eventually downshift on it's own in order to increase engine braking- like it knows what's going on! I've coasted down steep grades with the rpm's at 3500~, and it wasn't until I finally touched the accelerator that the transmission would upshift back into overdrive. Mind you these are descents that last like 10 to 15 minutes atleast.

So that is definetly one scenario that the automatic will hold a lower gear without any throttle inputs from the driver.

 

Nah I don't manually shift it, just the O/D Off button on occasion. I guess it's just normal for this truck. As long as it doesn't freeze up the trans I'm good with it.

 

First of all the Hill Descent Control is a switch that you activate and has more to do with controlling your descent crawling down steep grades in 4 wheel drive. I uses your breaks to control speed, etc.

As far as your description, it is perfectly normal although maybe not what you intended to happen. It all has to do with the grade of the hill (up or down) and load (or how much your press the gas pedal.) For down hill you need to press the break for it to activate and downshift for you. On up hills, if you floor it (or give it enough gas to downshift) it may not shift back into 4th or 5th if you're still on a grade, regardless of how much gas you're giving it.

It is more or less normal for what you describe - may not be perfect, in that I've experienced times when I'm going up hill and I think it could easily handle 4th gear, but refuses to shift out of 3rd. The only way I've been able to fool it in those rare cases was to accelerate to 70-75mph then back off the gas, it'll shift into 4th at that point even if I'm still going up hil... Also, if going up and you don't force a downshift by giving it enough gas, it won't automatically downshift until your speed starts to slow and you need to give it more gas to maintain speed - again though, it won't go back into 4th-5th until your off the grade (more or less.)

Edit: was going to mention something else. As I was saying it may not be a perfect system (up or down hill behavior) but it is a lot better than it constantly shifting up or down going up hills. In other words if you're on a grade where it would constantly shift between 3rd and 4th that would be really annoying, so keeping it in 3rd until you're done with you accent is better (though still annoying when you think 4th or even 5th would do the job.) Same deal with going downhill - it'll stay in the reduced gear until you're off the grade, even if you give it gas going downhill - more wear and tear if it is constantly shifting...