5th Gen Anti-lock Braking Issue on Ice and snow

I just had a bad experience with my 2021 4Runner Nightshade. Driving in Snow and Ice conditions the other day and it seemed like the anti-lock braking system was not working at all. At slow to very slow speeds on the snow and icy roads, the truck just slid when I tried to stop. Never pulsed the pedal or heard any clicking sounds, or other indication that it was working.
The truck has 40K miles on it.

Anyone experienced something similar in the ice and snow with late model 4Runners?

Also, during this drive, the truck got snow and ice all over the front end, causing parking assist alarms, and caused the crash detection system to act up, by alarming when not close to another car, and also switching off when the sensor got iced over.

Thanks,
Dan

 

Is it possible that you hit ice without snow tires and all your 4 wheels had 0 traction? For anti-lock to work, the car needs to know it still moving. It does so by looking at each wheel speed sensor. If none of the wheels are moving at all, the car would think it already stopped.

You have to old-school pump brakes. Also snow tires are a very good idea.

 

Thanks for the feedback Sin4r.
By the feel of the truck, I expect all four wheels were sliding at the same time in this case. I'll ask the obvious question here, isn't that the primary purpose of the anti-lock braking system, to prevent lock up of all four wheels and loss of control?

I tried to pump the breaks in one case, and it did nothing.
I spoke to one of the more experienced service advisors at the local Toyota dealer.
He said his Tundra did the same thing and gave me a similar explanation about all four tires locking/sliding and thus, the system not knowing its moving.

I own a 2009 G8 GT that also has anti-lock braking system, and it works to prevent lock up of all four wheels.
I've had similar happen in the ice/snow and it worked as expected, releasing/pulsing the brakes to save me.

Would like to get input from Toyota on this one.

thanks,
Dan

 

If the truck is already sliding and the wheels aren't rolling, the brakes are not in a locked condition. There's nothing an anti-lock system can do to bring them out of a condition that they aren't in. It also wouldn't help for it to just apply the brakes regardless of its normal logic, because if they are sliding instead of rotating, your truck will continue to just slide merrily along until it reaches something that isn't ice.

 

In ABS system design there's a parameter called slip ratio, which is the % of lockup and slip that gives the shortest stopping distance. The optimal slip ratio isn't 0%.
Remember ABS isn't magic. If you're on ice with shitty 20" all-season tires the stock Nightshade comes with, what you experienced was the best stopping distance your 5000-pound SUV could manage.

You can improve braking performance on ice by putting the transfer case in 4hi. On AWD models you'd want to lock the center diff.

 

Really? That's a new one. Please explain this logic. Not trying to be a smart-ass, but I've driven 4WD vehicles on snow and ice all of my life, and this is something I've never heard, nor experienced.

 

Practice somewhere (preferably open level ground) by applying a tiny touch of gas while gently depressing the brake pedal. This will allow the rear wheels to rotate and the anti-lock braking system to be able to detect the front tires have stalled out. This technique mimics the ATRAC system in my truck (which I've tested out on my last outing.) See if this works for you if you don't have ATRAC in your T4R so the next time it happens you'll have something to try in order to regain control.

 

Due to weight transfer, normally the front wheels provide 70-80% of the braking grip. Putting it in 4WD allows the rear wheels to contribute more braking grip due to the locked driveline. 14% better stopping in 4WD vs. 2WD in the Tacoma:



Since you have a Limited, you can experiment with this in an icy road or parking lot and compare braking performance with a stopwatch between center diff open and center diff locked. In AWD crossovers (Jeep Compass, Hyundai Santa Fe) I also notice a marked improvement in stability in turns on snow and ice with the center diff locked.

 

If all four wheels are locked up how will abs be able to tell a difference between that and being stopped? abs only works if there is traction and it sounds like you had zero traction. I would suggest you invest in better tires for the condition and/or don't just keep the pedal mashed all the way to the floor.

 

I highly recommend improving tires. It is rarely, if ever, I experienced 4-wheel slide on ice in any car that had snow tires equipped. Traction control is powerful safety enhancement feature, but it requires good tires to work optimally.

 

Since the purpose of ABS is to maintain some control when braking, I’m wondering if the computer decided that locking was the way to go to stop the vehicle when moving at such low speed and without steering input.

 

Gents,
Appreciate the comments. So, the 4Runners have no other means to discern if all four wheels are sliding/skidding?
That is still puzzling to me, when considering the reason for antilock braking systems. For example, if you're driving on the highway and it's raining, and there is an emergency braking requirement, all four wheels lock and you start skidding, and the anti-lock braking system does not work because all four wheels are locked.

During this drive in the ice and snow, the truck would slide almost every time I applied the brakes, and I was easing into applying the brakes, and letting off as it started sliding and easing into them again and it would slide to a stop. I was going slow, and it was behaving differently than it did at previous times on ice and snow, so the only difference I can figure would be the tires. I still have some decent tread left on them, like 5-6mm. I even tried once to turn the wheel a little bit while braking, and it just kept sliding.

I will try locking the center diff/using H4L in the next opportunity, but its March in St. Louis and we may not see any more ice or snow this year.
New AT or MT tires will be installed before next winter.

thx.

 

They have wheel speed sensors. Unless those are damaged, it knows whether the wheels are turning.

That is not what I would expect. If the wheels are locked, the ABS will release them for short intervals as expected, assuming they detect the wheels turning during those intervals.

If I recall, in the ice scenario, you said you applied the brakes after a 4-wheel slide had started. In that case, the some or all wheels may not have been turning at all. In that instance, neither locking up the brakes nor releasing locked brakes is going to decrease stopping distance until some tires are on a surface with enough traction for them to turn. In the rainy highway example there's nearly always enough traction to turn some of the tires on wet pavement.

 

If the driveline/wheels are not spinning, how do you expect the car to know it is moving? You need to give it something to work with

 

This is not the way to properly use ABS brakes - just FYI. ABS brakes by design "pump the brakes" as a system (that's a laymans way to put it). To properly use ABS, you should hit the brakes and keep steady pressure on the pedal and the system will do it's thing. I suggest taking a defensive driving course to learn how to properly use the systems as designed for emergency use.

 

I've had better luck pumping the brakes vs. steady pressure on snow and ice. Despite being the "wrong" way to use them.

It may be like gravel, where locking up and digging in will actually stop you faster than keeping the wheels turning. It takes so little to lock up, essentially the ABS has you doing zero braking instead.

 

I’ve had the abs cycling the brakes at slow speed (1 to 2mph) and refuse to stop, which was annoying because sliding would have been a quicker stop.

The weird behavior (either activating or not activating abs at very slow speeds) seems to be dependent on various factors baked into the logic of the system. Which don’t seem easily predictable to me.

I like the reminder that 4wd (w center diff locked) can actually reduce stopping distance and help
Modulating them at the threshhold. Need to remember that next time.

 

I have no idea about winter driving, Florida ice (light rain on hot oily pavement) is bad enough. The real thing scares me to death actually lol.
I was wondering, in certain situations could the trans brake possibly cause the loss of traction before the brakes are applied? On a Limited, the trans brake might affect all 4 wheels?
Ive noticed at slower speeds, on slight downward inclines when you let off the gas the trans brake kicks in, quite significantly at times.
The transmission programming has definitely been the subject of numerous threads and complaints.