ABS and VSC not working

[Evancool]

So we had ice yesterday and...I plowed right into a brick encased mailbox. Even though I was going about 10 mph the street started going down hill and was already iced over so no chance of stopping.

The brakes locked and vehicle started going sideways into the curb and eventually into the mailbox doing a 180, finally stopping against the curb. During this time, all four wheels were locked, ABS and VSC were dormant. The diff lock was off so VSC should have been active. Neither tried to help stop the vehicle.

Usually when ABS is active I can feel it rapidly pump the brakes and VSC will sound an alarm and try to correct the direction. Neither activated so I wonder if both systems have failed or there is certain criteria for them to activate.

A couple months ago I tested ABS on a icy parking lot and at that time it worked.

 

[Inv4drZm]

I'm guessing all of your tires were locked up therefore your wheel speed sensors never registered a difference in speed between them and never activated the electronics. I doubt it would have helped either, if all 4 wheels were already locked up.

 

[AuSeeker]

I'm inclined to agree, if all 4 wheels were locked up the 4R for all it knew was parked or stopped so no reason to activate either system.

 

[Evancool]

Hmm...doesn't that defeat the purpose of ABS though? The technology in a 2007 vehicle should know when it is still in motion even with all 4 wheels locked, I thought that is how ABS is supposed to work when one or more wheels lock when braking. I wonder if a 2017 4Runner's ABS would react the same way.

 

[ElZilcho]

I'm inclined to agree, if all 4 wheels were locked up the 4R for all it knew was parked or stopped so no reason to activate either system.

I'm guessing all of your tires were locked up therefore your wheel speed sensors never registered a difference in speed between them and never activated the electronics. I doubt it would have helped either, if all 4 wheels were already locked up.

Ditto. All four tires locked at the same time and the computer didn't know skidding from stopped. ABS/VSC are designed to intervene at a wheel slip angle between ~3-5%. Too sensitive and ABS/VSC would kick off any time you hit a bump or drove over sand; any less sensitive and... well, you go sliding into mailboxes. It's designed to be as unobtrusive as possible and still work in 99.9% of situations. At low speed and super low traction you found the 0.1% of situations that fooled the computer. A 2017 would do the exact same thing.

I slid an Avalon through an icy intersection at about 2 MPH a few years ago doing the same thing and had to make awkward eye contact with everyone at the cross light. It was the most awkward 45 seconds of my life. So slow. Me sliding... them judging. hwell:

Seriously though, sorry about your truck; that sucks. It's worth slamming on your brakes in a gravel lot to test the ABS but I think it's unlikely it's failed.

 

[Evancool]

Thanks everyone. I learned more about how the systems work now. I'll just need to be even more careful going forward...or backwards.