Traction Control operating while "D" and rolling backwards

[rob_macca67 Avid PP Poster! Find all posts View Profile Close rob_macca67]

Hey Guys.....

I just came across a situation which I hope is normal..... While stopped on a incline & in "D", I took my foot off the brake just so I could roll the vehicle back a bit... 5mtrs or so (Auto still in "D"). To my surprise the Traction control light came on in the Dash and Traction Control started to operate..... Is this normal with these cars ?? I assume it is, but I've never came across this b4

cheers....
rob

[Case Member Find all posts View Profile Close Case]

To my knolage it is
i have a 120 series Grande (very similar driver assist tec to the 150 series) Its part of hill assist control "to Minimize vehicle rollback"

just whack in N and then roll back

After saying that i dotn have a 150 so i could be wrong, it happens more often then not
Case

[Guest Close Guest]

Yes this is normal.

Its the Hill hold fuynction, it holds the brake for a fewseconds until you start to move forward.

On "SOME" hills though of more than average steepness, it will occasionally not hold and the traction light and clunking / brakes will apply.

I have one hill on the trip home that does it "every" time.

Its just the way it is.

[davidsford Member Find all posts View Profile Close davidsford]

It does this on my driveway all the time, scared the s*&t out of me the first time it did it with all the clunking and clicking going on.

[MDS69 Advanced Member Find all posts View Profile Close MDS69]

Hey Guys.....

I just came across a situation which I hope is normal..... While stopped on a incline & in "D", I took my foot off the brake just so I could roll the vehicle back a bit... 5mtrs or so (Auto still in "D"). To my surprise the Traction control light came on in the Dash and Traction Control started to operate..... Is this normal with these cars ?? I assume it is, but I've never came across this b4

cheers....
rob

I would be more concerned about rolling backwards against the transmission whilst it is in D for 5m.

[rob_macca67 Avid PP Poster! Find all posts View Profile Close rob_macca67]

I would be more concerned about rolling backwards against the transmission whilst it is in D for 5m.

Well, it probably wasn't 5mtrs as I didn't get out to measure it..... but I can't see that doing any harm..... I know of people when 4wdriving in steep terrain who, when descending down "really" steep sections, they put their Autos in reverse while heading down to assist in the braking/controlling the descent..... They obviously keep this to a minimum (& a last resort) due to the heat build up in the Auto though.....

[Corigator Avid PP Poster! Find all posts View Profile Close Corigator]

... I know of people when 4wdriving in steep terrain who, when descending down "really" steep sections, they put their Autos in reverse while heading down to assist in the braking/controlling the descent....

Rob,

That surprises me.
I would think that would not be good for a transmission. I have yet to find a slope where low range first doesn't hold me sufficiently to do a safe descent. (perhaps with a touch of brakes)

[MDS69 Advanced Member Find all posts View Profile Close MDS69]

Well, it probably wasn't 5mtrs as I didn't get out to measure it..... but I can't see that doing any harm..... I know of people when 4wdriving in steep terrain who, when descending down "really" steep sections, they put their Autos in reverse while heading down to assist in the braking/controlling the descent..... They obviously keep this to a minimum (& a last resort) due to the heat build up in the Auto though.....

Now I am really concerned. I wouldn't even do that in a rental.
Now I will admit I am not an auto transmission specialist but that can't be good.
Would be good to hear from someone qualified on autos about this practise.

[wooley Avid PP Poster! Find all posts View Profile Close wooley]

Well, it probably wasn't 5mtrs as I didn't get out to measure it..... but I can't see that doing any harm..... I know of people when 4wdriving in steep terrain who, when descending down "really" steep sections, they put their Autos in reverse while heading down to assist in the braking/controlling the descent..... They obviously keep this to a minimum (& a last resort) due to the heat build up in the Auto though.....

That sounds like a terrible idea. I'd be avoiding moving in the wrong direction to which the gearbox wants to drive.

[avj Junior Member Find all posts View Profile Close avj]

Ours did this last night on my very first drive when my got it home from the dealer.. It scared both of us... seeing it only had 100km on the clock and did not know it was going to happen...

Glad it is nothing to serious

[rob_macca67 Avid PP Poster! Find all posts View Profile Close rob_macca67]

That sounds like a terrible idea. I'd be avoiding moving in the wrong direction to which the gearbox wants to drive.

I'm not talking about Prados here and the hills I'm talking about are VERY steep..... and it's a LAST resort type of thing and u obviously don't do it for a long period, but it does work and u use your accelerator as your brake so to speak.... It's something I wouldn't do in my Prado as I wouldn't take my Prado on those sort of tracks...


Plus... Come to think about it, I don't think it would work in a modern 4wd's with all the electronics of Traction control, etc

[ursos Member Find all posts View Profile Close ursos]

I'm not talking about Prados here and the hills I'm talking about are VERY steep..... and it's a LAST resort type of thing and u obviously don't do it for a long period, but it does work and u use your accelerator as your brake so to speak.... It's something I wouldn't do in my Prado as I wouldn't take my Prado on those sort of tracks...


Plus... Come to think about it, I don't think it would work in a modern 4wd's with all the electronics of Traction control, etc

I was taught this technique years ago in an advanced 4WD course in my 80 Series LC. It is much more effective and safer than brake feathering but agree with all your points: (i) only for very steep slopes, (ii) should only be done for short periods, (iii) probably will not work with modern electronic control mechanisms. Advice in the course was to only do this if you really have to, i.e., when it would be even more 'dangerous' or impossible to try and turn around or reverse back up the hill but you probably shouldn't have gotten yourself into this position anyway...

[Peterpilot Avid PP Poster! Find all posts View Profile Close Peterpilot]

I was taught this technique years ago in an advanced 4WD course in my 80 Series LC. It is much more effective and safer than brake feathering but agree with all your points: (i) only for very steep slopes, (ii) should only be done for short periods, (iii) probably will not work with modern electronic control mechanisms. Advice in the course was to only do this if you really have to, i.e., when it would be even more 'dangerous' or impossible to try and turn around or reverse back up the hill but you probably shouldn't have gotten yourself into this position anyway...

From my limited understanding of auto transmissions, this relies on the torque converter to slow the descent of a vehicle whilst moving forward in reverse gear and with the engine operating at an RPM below that which would cause the torque converter to lock up.

What a can of worms this technique opens up, and I am surprised that this technique is actually being taught by some.

Back to Rob's the original question, what you describe this is what Toyota call Hill-start Assist Control (HAC): http://www.toyota.com.au/glossary/f-j

Hill-start Assist Control (HAC)

Automatic function that prevents the vehicle rolling downhill when starting off. It is particularly helpful on low-traction surfaces and when driving off road.

This Toyota system is not a "hill holder" which normally works by keeping the brakes on and not allowing the vehicle to move backwards at all when brake pressure is released on an incline until the car moves forward.

[Steve M Addicted PP Member Find all posts View Profile Close Steve M]

Have a friend who worked for a trans place (Blacktown) and I know when I had my commodore he always said to me, never ever ever put the commdore into drive while still rolling back as it will strip the main shaft. Well a lday here at my work use to do it everday, reverse out hit drive without even using brakes and take off, I warned her about it, cost her $1500 for a full rebuild. He said your going one way then you expect the tranny to the decide to spin the other way instantly big no no...............Not sure if this would do the same damage using it as described above. Our drive is fairly steep and while waiting for the electric door to go up I made the wife use the left foot to hold (both cars,both auto) and then just as she starts to accelerate lift left foot off, do this to stop rolling back against transmission

[barajak Senior Member Find all posts View Profile Close barajak]

I would not go down a steep decent in reverse however I have backed down a hundred meters or so in 'D' before but i don't know if the electronics will allow that in the Prado. Last winter I was going up a steep rocky slope in my one week old 150TD and came upon some recent rework in red clay, lost forward motion and slid back a car length or so before it stopped. Now I could not go forward and I could not even stand up on the clay. Nearly lost it is reverse with brakes as you have no steering and nowhere near enough engine braking for the conditions. The answer is to pull the handbrake on hard and drive the Prado back against the park brake, lift your foot and you stop and you keep full control of the steering. You can do the same thing going forward, 1st low range, centre lock on, hand brake as much as required and drive it forward. Yes I might have to spend a few bucks on the park brake before most owners but it will be small change compared with a trans rebuild and I have lots of fun in the bush. Don't consider going down a mountain using 'Down Hill Decent', you will run out of brakes before you get to the bottom.