Using the S-shift does not "disengage" the computer from sensing the road conditions and engaging VSC/TRAC. Also, 3rd Gen Highlanders have a warning system that will sound and not allow the gears to be shifted if the driving circumstances are considered dangerous. Toyota does not specify what they consider dangerous, but I assume that would be a driving 60 MPH and shifting into 1st situation that would over-rev the engine and transmission.

 

Yup, the main factor is gearing, it won't downshift if you're outside the gear range.

 

Wow, very good question because I hadn't thought of that. I bet it would be disengaged. If I had a 3rd Gen, that would be something I'd be testing because it would make a huge difference on those long, snowy downhills. The only time you're going to be able to guarantee it's engaged is if you're below 25 mph and lock it in.

 

I hope someone has the answer to the OP's question, 'cuz we live in Colorado like he does, and I have gotten used to downshifting on the looong downhill mountain grades, like from the Eisenhower Tunnel down to Silverthorne, to keep from excessively speeding. So, this is as important to me as it is to the OP. Although, we don't ski any more, and totally avoid going over the mountains to Denver if there's inclement weather. Sometimes it can't be helped though. Yes, if we have no option but to drive over in a snowstorm, we take the 4Runner.

 

I hope someone has the answer to the OP's question

Refer to the Gen 3 owner's manual, it's in there. It would make no sense to shut down VSC and/or TRAC simply because of a change in gearing selected by the driver.

 

I'll throw this into the convo since it seems to relate to the general idea of this thread. I have noticed that when I am driving with cruise control on and hit certain hills in my neighborhood, which are rather steep, that I notice the RPMs start to increase, say into the 3000+ range and my vehicle appears to try to maintain the set speed on cruise control. For instance, this one pair of hills approaching my house, CC set to 41 (speed limit 40), without me doing anything once I crest a hill and start down the backside I see the RPM increase rapidly, vehicle does increase in speed somewhat but I can tell it is not going full tilt. It goes up maybe 5-9 mph over the set point maximum but doesn't easily go more than that. Other vehicles I have owned prior would easily cruise to 60+ if left unattended by me but the HL holds it back in the under 50mph range. I actually like it. It is very reassuring descending these hills and I almost never feel a need to brake even as it goes around corners and such. This is a small rural road too, not a main highway. It is counterintuitive to me how increasing RPMs equates to braking of the vehicle but that seems to be the case in this instance. BTW, it doesn't happen on just any hill, there seems to be a certain grade when it kicks in otherwise it will cruise with increasing speed like I was always used to.

 

It is counterintuitive to me how increasing RPMs equates to braking of the vehicle but that seems to be the case in this instance. BTW, it doesn't happen on just any hill, there seems to be a certain grade when it kicks in otherwise it will cruise with increasing speed like I was always used to.

An increase in RPMs when going downhill with CC on in order to maintain the set speed would indicate that the transmission is downshifting to a lower gear and using engine braking (a part of the OPs initial question) to hold the speed down. Pretty much what all good CCs will do.

 

As the OP, I will give at least a partial update on this question. We got snow on Tuesday morning and so the roads were very slick heading into work yesterday from just outside Denver. I was not on a really long, or steep grade, and speed limit was 45, but I was able to engage the sport shift to use engine/transmission braking. So far, it seemed to be fine.

Observations:

HL was very stable, did not notice any tendency for the rear end to try to pass the front end. No VSC/TRAC engagement occurred.

I had it in snow mode, not sure this made a difference.

The monitor of the AWD system on dash showed power going to neither the front or rear axle. Clearly, this was not the case because the car was slowing down or holding speed with the forced higher engine RPMs.

Another word of caution for anyone who tries this, I do have brand new snow tires on the HL so it is possible that this contributed.

If I get out on I70 and do a real test in the harshest conditions, I will post another update.

 

Admittedly the AWD setup is different for the 3rd Gen compared to the 2nd Gen, but then again I assume the sensor/computer setup the two systems must be very similar. Anyway, I've had my 2nd Gen Highlander in three types of downhill situations driving in S-mode when the VSC/TRAC system engaged. Two were on ice and one was on a steep, rain soaked street covered in pine needles (and for anyone who has driven on the latter they know it's very similar to driving on ice), and in each case the traction control system kicked in, beeping away, the brakes chuddering, and the Highlander held the road like an Alabama tick. I've also gone as far as driving my Highlander downhill and high speed on more than one dirt road and intentionally fishtailing forcing the traction control system to engage, and each time it did--as I like to say--as though the hand of the Almighty reached down and quickly and securely straightened my Highlander out without any input from me. Impressive to say the least!

It's admittedly a supposition, but I suspect the 3rd Gen would do the same thing under similar circumstances.

 

So I finally had a chance to check out the HL in a long descent, locking it into 3rd or 2nd gear to "engine brake" on slippery/icy roads. No problems whatsoever with feeling a lack of security and experienced no vehicle stability control engagement, whether I was applying brakes or not. HL was pretty impressive.

 

You want to experience the ultimate in engine braking control and stability management? Try engaging DAC some time on a very steep or slippery hill/slope. Click here to read a past thread discussing DAC. One word to describe DAC: Awesome!