Engine Stall during Hill Assist

Hello all!
I am not exactly sure what to call the "feature" that keeps you from backing down a hill when stopped and you take your foot off the brake? Hill Assist? I hate it.

I was driving up a snowy/icy hill. I hit a patch and my truck slowed to a stop. The hill assist kicked in, and suddenly I am careening backwards down the hill. Brakes not working and steering not really working.

Luckily I slid straight down the hill with cars parked on both sides, and hit nothing! Miracle.
Once I was at the bottom I noticed the engine was completely off. It stalled out, hence the lack of brakes and steering.

Is this normal?

I instantly started heading backwards down the hill when the truck came to a stop. I didn't have time to, nor would I have, turned the key off and back on?!?!?!

It scared the crap out of me.

Does anyone have an explanation? Is something wrong? Or was it just a fluke occurrence?

Thanks!

 

HAC - Hill Assist Control. It's not meant to hold you, only to slow the roll back. Just hit the brake or step on the throttle and it will stop.

 

Yes, I know how it works. I am just curious if stalling out when not applying the brakes is normal. I was trying to continue up the hill, tires spin, rolls back a bit, then stalled out. Then no way apply brakes effectively.

 

You can stall out an auto if you roll backwards fast enough in drive especially if you rolled back in low range. It will spin the turbine side of the torque convertor backwards fast enough to stall out the engine.

 

Hmm. 4Runners don't have "Hill Assist"?? But i know the feature that helps prevent rolling backwards when transitioning from Clutch/Break to gas.

My 2014 Mazda 3 had it and it was awesome, just don't let it do "Hill Assist" for too long or it will release and roll backwards, then likely stall out the vehicle. Drive is for going forward, so if you roll back it will likely stall the vehicle. How did you ever drive without "Hill Assist"???

 

That is dangerous.... A stalled out vehicle rolling backwards with no easy way to stop it?

This does not seem safe or correct. Yet it happened to me. I surprised this doesn't come up more often on icy streets going up hills.

Is it possible to disengage this? Especially when in 4Lo.

 

How do you roll backward enough to stall engine but not go forward? Sounds like you should of had enough traction so the wheels we turning.

 

Neutral or reverse (if rolling backwards) will prevent engine stalling when rolling in the opposite direction of the gear you're in.

Unfortunately it's automatic because FeAtUrEs. Maybe if you pull an ABS fuse but then you lose other stuff.

It's their hill hold without using an electronic parking brake like modern cars.

 

It'll do that if you don't give it enough gas or switch to a more appropriate gear.

 

Also, it will throw a warning light before it stalls, so you'll have enough time to hit the gas if that's what you choose.

 

I was on an icy hill. The wheels were spinning. Then when it sliding backward it stalled out.

There was ZERO time to shift to N or R.

I was constantly on the gas until it stalled. I was in 4WLo if that matters.

 

Ice.

 

This is likely a combination of bad icy conditions & user error, not the vehicle or feature. Plenty of people get in accidents because of ice and not being able to control their vehicles as they hoped.

It's just like driving a manual and not letting out the clutch just right in first gear on a hill before it rolls back and stalls.

Next time let those tires spin till you decide to stop.

 

Staying on the throttle should have cancelled it HAC. Shifting to neutral or reverse would have cancelled HAC.

Rolling back and stalling in drive is just automatic transmission things.

 

Yes but stalling while going backwards requires the wheels to be spinning in reverse while in D.

If you are sliding it shouldn't. Like whipper said staying on the gas should of kept it from dying.

 

This sounds like a scary situation, there was another thread a while back that linked a vid that shows how easily things can go south in this exact type of situation. Glad you got through it unscathed.

However, I don’t think turning off this feature should be a goal. I mean, the feature failed to prevent you from stalling the engine. It didn’t cause it.

In fact, now that I’m starting to realize how dangerous it is to roll backwards down hills in sketchy off-road situations, I think I’m starting to appreciate the aggressive brake application as a good thing. And, now I wonder if it’s so aggressive precisely anticipating off road situations to avoid stalling and loss of brakes/steering.

Maybe it failed to prevent a stall because of the fact the rpm differences it experienced…going from revved up to reversing directions may have been too much of a shock? In any case, good to know it’s not infallible.

https://www.4runners.com/threads/this-is-why-you-leave-space-in-front-of-you-when-off-roading.35362/

 

Question to you guys in the know. There was a video a few days ago where a Bronco failed to navigate a hill off-road, engine stalled, and the truck rolled backward with difficult braking and crashed. In your view, did the OP experience something similar?

 

Yeah, that’s the one I added the link in my previous post. I’m willing to bet that’s what the bronco experienced. Hard to say for sure, but it’s probably more useful to view these situations as a driver mistake that the safety systems were not able overcome. I think the lesson here is that allowing the tires to roll backwards on a hill is a critical mistake with potentially serious consequences. Really, in an automatic, it’s probably best to be ready with your left foot covering the brakes as you climb.

Truth be told, I’m surprised to realize that automatics can stall the engine as quickly as it would happen in a manual transmission vehicle. It’s not something I’ve really thought about before. But now it’s on my mental checklist for the next time I’m doing a steep climb.

 

You know what? I just remembered that the Bronco was manual…right? So a little bit different scenario?

 

I have a feeling this thread has some legs.

I'm getting in early on this one:

 

The core issue of losing brakes and steering is the same.

Both a manual and an automatic can stall. Once you stall, your brakes are gone if you lift up on them, and steering will be very difficult. On a steep hill, this can turn into a life and death situation quickly depending on how far you have to roll. What happened to the bronco after it stalled, will happen to a 4runner just the same, and any other automatic vehicle.

However, how you avoid stalling of the engine will be different for a manual vs an automatic. For an automatic, using your brakes immediately to *before* any roll back will protect the engine from stalling.

 

Keep in mind the Runner would still have power brakes due to the booster pump.

 

Although brakes might not be very useful on ice. My philosophy on icy hills is not to start anything I may not be able to finish. Once gravity takes control, I'm just a passenger and hopefully not a victim.

 

Also that. I stay away from ice. It’s not hard to do in CA.

 

I was going to say in the OP's original scenario, once that 4k+ pound vehicle started sliding backwards down the hill on ice, no electronic gadget, functioning or not brakes, wheel spin or not, or engine running would have prevented it from continuing downward on the ice.

 

Good point, that might potentially prevent loss of brake pressure on 4wd 4runners equipped with the electric booster.

Does anyone know if this system is a supplement to vacuum generated by the engine? Or is the electric booster the only source of boost?

If it supplements vacuum from the engine, I wonder if the electric pump could generate sufficient boost on its own if the engine cuts out.

 

The pump is the only source. There is no hose to the intake manifold and no donut booster on the firewall.

 

I do not believe they have a traditional vacuum brake booster.

 

Thats the thing. I was on the gas constantly until the car started backwards. Then it was all trying to brake. I was not going very fast at all, 5 mph if that, adn normal brakes would have stopped me, but I was stalled. And brakes DO NOT work when the engine is off. Same as steering.

 

Yes they do.

This doesn't for sure because the pump stops turning.