Im a t4r newbie and totally lost in this senario... About to go into the dealer and could use some indication of WTF happened to my truck before I lend it to my parents for a week.

I was driving around Phildelphia this past weekened and about 25 minutes into my trip on a minor highway. We were going between 40-50mph as I started to descend down a half mile hill I let off the gas to coast. Soon after my truck began rev'ing the engine very loudly (or at least it sounded that way). Using the brakes to slow to truck did not calm the engine to a "normal" sound. It seemed (sounded like) i was gaining speed (from gravity i think) and observed I was not noticeably gaining speed on the dash nor did my rpm's seem high. I have never heard this loud rev'ing sound before and began to pull over while lightly applying the brake. The sound continued as I reached the flat road at the bottom of the hill and ran out of shoulder to pull off onto. The truck didnt seem to accelerate normal for a few moments but I carried on up the road about half a mile and pulled over at my destination. Upon restarting my truck to drive home things seemed normal. (normal as much as it can be considering I still dispute that the vibrations and hard shifting/stuttering are not normal) Why the loud rev'ing occurred I have no idea, please help!

Is this a normal function of the truck? I had previously asked about the resistance while coasting to a stop... could this be a similar function of the truck? If so, does anyone else find it invasive, or do I need to be schooled of why that happens in the first place? Also could the hard shifting/stuttering and this rev'ing thing be symptoms of some other issue/concern?

I'm going to be lending my truck to my parents in a few weeks while im away and dont want to worry about potential safety issues. Thanks in advance for your help.

That's grade logic in action, it is completely normal. As you were going downhill, the transmission downshifted. That is helpful going down long grades (particularly when towing), to save the brakes by using some engine braking to control speed.

Most all automatic transmissions have grade logic these days.

Being the neophyte here I'm gonna say 'DOWNHILL ASSIST CONTROL'. Check the owners book for details on how it operates to be sure!

Also, I'd wait for others to log in and offer their opinions on this!

Mike

Thanks again.. that puts my mind as ease! Looks like i'll be reading my manual some more.

i was going to say it sounded like the car down shifted. But, i was going to ask if you were in manual mode, but, i guess it's a feature. as M1911 pointed out.

I think it is doubtful it is Downhill Assist Control at those speeds.

I do agree about the transmission doing though. My 4th Gen does it too. I would agree that it is more prominant in the 4Runner's vs other vehicles I have driven.

I believe DAC only operates in 4Lo - it was just routine downshifting by the tranny as it sensed the gradient you were going down.

I consider it a reminder that the sport mode is a better choice on mountain roads. I've also had it not upshift in this condition when gas was applied. That was annoying but only happened once so far...

and only works below 15MPH and shuts off if the brakes are pressed. The slip indicator would also be flashing. As some are saying, I think it is the tranny downshifting.

It' not DAC for sure. I had similar behaviour when I put shifter in manual mode and drive downhill on 2nd gear. It was a slippery hill, RPM were 3000-4000 and it sounded quite uncomfortably, but I didn't really have choice.

When transmission is on "D" I don't recall I had any exessive engine RPMs when I let off the gas coasting downhill. Could be it's just I didn't coast long enough though.

"quite uncomfortable" is a good way to describe the rev noise... it seemed excessively more than anything i would normally hear. I was in "D" and thought to check my position when the noise first occurred.. still there. When the rev noise started i wasnt sure if the high rpm's would continue to increase, level out, or what... checked the rpm gaugue and i believe it was at/around 2500. if it had been in the 3000-4000 range i wouldnt have been as startled. Even when i slowed my decent the noise was still loud and rpm gauge around 2500. That was the holy $hit moment for me knowing i had no explanation for the passengers or myself. Thanks to everyone talking though it.

As you described it I don't think it's normal. I was driving over some hills but there is still possibility that I didn't face exactly the same conditions. So unless others confirm that downhill downshifting is a normal thing for T4R I would probably try to reproduce this to have clear pattern and then take it to a delaer, asking them either fix it or update user manual : )

I can live with tranny downshift and the grade logic kicking in (it was a long hill). Maybe I'm not use to newer suv's yet. I'm going to read into the manual a bit tonight and look for the "sport mode" and mention of causes for down shifting in those situations.

Mine does this at least once per week on a slight downhill Onramp to 95. The tranny gets a little confused and refuses to upshift from a lower gear- in my case it's 3rd. I usually get off the gas for a few seconds and then...... It decides to shift. Annoying- hopefully Toyota can reflash my Ecu and fix it.

Isn't the transmission the same one in the FJ Cruiser and V8 equipped 4th gens?

If so they have the Artificial Intelligence with them

Look into the FJ Cruiser stuff at Toyota

Go to Engineering-Powertrain-5 Speed Automatic and watch the little video on the transmission.