I have noticed a few times recently that when I brake hard the wheels lock up; that is, I can hear the tires skidding on the pavement. I had thought that the ABS kept the wheels from locking. It has happened at highway speeds and at slower speeds. This is new behavior - I have not had the wheels apparently lock before a couple of months ago.

It happened several times before I realize what was bothering me about the noise I hear during hard braking. Also, I don't feel the brake pulsating during these quick stop episodes.

There are no codes in the SG or warning lights. I think it is unlikely if not impossible for the ABS to malfunction but throw no codes?

EDIT: Oops, check the TITLE as well as the text, before posting. The title of this thread is, of course, Wheel lockup, not Whell lockup (whatever that may be)!

 

Just to clarify, are you hearing the tires squeal or are you actually hearing the tires scrub the pavement?

Almost all tires will squeal as they reach and slightly exceed their maximum point of grip (as experienced with a tight turn) but that doesn't mean that they are skidding (out of control) per se.

That said, I've never intentionally hit the brakes long/hard enough to test the ABS on my 08 FEH but I have made the tires squeal a few times. Once a 70+MPH when a semi decided to change lanes as I was passing it, and again at low speeds when traffic came to an abrupt stop while cresting a blind hill. In both cases the FEH slowed as I expected and the vehicle remained straight and true.

 

It is a squeal, but I'm not sure how to tell the difference without getting out of the vehicle and looking at the pavement. Maybe all is well...

Actually, it is probably the new tires I got. I had a piece of metal go through the right rear tire, so I replaced both the rear tires. I was scheduled for my 5K oil change shortly after, so they got rotated to the front. But the different tires would explain why I'm hearing the noise. I replaced both left and right rear (now front).

 

Its been awhile since I saw this. The tire industry has put out that a wheel rotation of ~85% is where the max point of braking occurs. IE the wheel is rotating at 85% of the rate it would rotate at if free wheeling for the speed.

So if you were braking hard it is likely you would hear such tire noise with the system working just fine. On the other hand your noting that it seems that the lack of anti-lock sensations in the pedal and maybe the lack of noise of it kicking in would seem to be of greater importance.

Just a thought.

 

Is this a recent change? Mine has started doing this just about at the transition point between regenerative and frictional braking. I suspect a cracked tone ring, but have been too lazy to crawl under and verify.

 

At the exact instance of ABS detection (prediction..??) of impending wheel lockup the TC system "messages" the HSD system that regen braking, front wheel ONLY braking, MUST be immediately discontinued. The 2010 Prius TSB indicates quite clearly that the HSD system, assuming it gets the message, does not always act on it expeditously.

If the HSD system's primary ECU happens to be too busy at the moment (it happens) to act on the message then a serious enough level of regen braking might continue just long enough that ABS's release, pumping, of the frictional braking system will have no noticeable effect.

 

Bottom line, Steve has a FEH and I'll bet that the braking system/ABS programming on an FEH, is, most DEFINETLY is, different than the Prius.

 

And I'd bet that they share the very same basic source code.

When you have a cross-licensing setup like this why would you bother to do, pay for, the same work twice...?

 

Not to mention the 2008 has no TC.

And also not to mention that TC affects acceleration (individual wheel slipping, activate ABS on that wheel to fix), not braking.

 

For the FE & FEH TC is considered a part of ABS, or vice versa. TC cannot be fully functional absent an ABS pumpmotor/system. TC, Traction Control, has ALWAYS been standard on the F/awd version FE and therefore the FEH. The early versions simply engaged the rear drive automatically in the event wheelspin/slip was detected. The "mid" versions were somewhat more functional, braking and dethrottling, and only with the advent of stability control have all the modern day aspects become available on the FE and FEH.

I assume stability was added to the mix in '09..??