I got a 2007 Toyota Highlander last summer with 135,000. Drives really well but can’t figure out this weird thing it does! I’ll be driving anywhere from 45 mph and up and it seems that the brakes engage. I’ve been experimenting to try and figure it out so here’s what I know: there is pressure on the brake pedal and when I pull over and tap that it releases the brake hold. I’ve tried to pop it into neutral and back into drive when it happens, but that does nothing. I had the front brakes and calipers replaced which only made the grip stronger when it happens! There are no lights or bells when it happens though I do have an ABS sensor that dings every time I go around a certain curve when the tire pressure is off, so I know that works and what it feels/sounds like. Could this be a transmission issue? A computer problem? Mechanics haven’t been very helpful. One more thing, I have a roof rack that provides probably too much wind resistance, could that trigger something? Again, no warning signals go off when it happens at totally random times.
The next time it happens, see if one wheel is hotter than the others. Check the temperature near the center of the wheel. It might be hot enough to burn you. For 10 to 15 bucks you can get an infrared temperature gun and point it at each wheel. I’m thinking warped rotor and/or blocked brake hose and/or bad wheel bearing with blocked brake hose.
I like the blocked brake hose theory. Old brake hoses tend to degrade internally. Calipers and pads were replaced so it SHOULD eliminate them from the list.
The calipers are probably cheap aftermarket parts and some are defective right out of the box.When was the last time you had the brake fluid replaced?
some other ideas to entertain:
#1. brake booster problem resulting in an unintended application of the brakes with no pedal press?
#2. stability control system deciding to “correct the course” based on wrong sensor readings?
#3. ABS unit misbehaving?
and… was the brake fluid EVER replaced on this truck? 
I’ll keep that in mind and check next time. I did just have rotors replaced
Thanks
Blocked brake hose theory - will ask mechanics about this… (dealership mechanics are the ones who have seen it)
Not sure if fluid was ever replaced… I had the front brake caliper and rotors all replaced by Toyota dealership. . and sensors work but not when this happens… with a brake booster problem would there be a build up of pressure on the brake pedal that is released by pressing it?
I did have the brakes done at Toyota and the problem happened before it was done as well as after so not defective calipers… brake fluid- how could the quality of the brake fluid cause this?
The boiling point of brake fluid is important.Old brake fluid has more moisture in it,bringing its boiling point sooner than expected and causing brake fade and all type of problems.In your case,I would check the rear brakes instead since the front brakes seems to work fine.
I’m mostly throwing ideas against the wall.
In theory, brake booster operates by the vacuum, but force is released/controlled by some mechanism connected to the pedal input.
If we assume that that mechanism somehow misbehaves, it could allow the vacuum to apply the pressure with no pedal press.
There are professional mechanics in this forum, I hope somebody of them will tell I’m dead-wrong or will give some details.
I’ve driven my 2007 Highlander with a pretty big, square roof-mounted cargo bag and that never triggered this type of problem, so I’d rule that out. I have had nothing but trouble with my Highlander’s brakes. I like the idea of testing the temp of each wheel. Hey mechanics, could a wheel bearing cause this? My Highland also likes to eat those. Last, my 100K Highlander’s latest brake mishap was a frozen parking brake. I’d check that too (I’m sure your mechanic thought of that). Let us know if you get a resolution.
Thank you. The mystery continues!
I wonder if changing the brake fluid would help. You ask why this would help. Aged brake fluid is hydroscopic; meaning it can weaken due to absorbing moisture. This lowers the boiling point of the fluid and makes it expand.
Several decades ago there were some issues with the disc brakes on Harley motorcycles. The rear brake caliper would lock up randomly and suddenly. This was caused by the brake fluid acting up as I mentioned.
This brake lockup happened to both a friend of mine and me. A Come to Jesus moment for sure.
A fluid change cured both bikes. Just something for consideration anyway if an obvious problem can’t be found.
To answer your question of whether a wheel bearing can cause this behavior, the answer is yes. When bearings go they allow the rotating assy to become “cockeyed” in the caliper which will drag the brakes and create a lot of heat. Then it just snowballs from there.
Another possibility has emerged! The master cylinder and the rod that goes into it… either adjusted wrong or the pin hole is clogged… make sense? Thanks for all the feedback. It has been helping!! Getting to the bottom of this!
If the MC rod was the wrong length or the pedal/MC wasn’t adjusted for the correct free-play the brakes could be slightly applied all the time. Seems a possibility, but an unlikely one. It’s pretty easy for a shop to test the free-play so if that was the problem you’d think they’d already have found it. If one of the small holes in the MC was clogged that’s a possibility too, and to me seems more likely than the free-play idea. Replacing the brake fluid and the MC would work if that’s the problem.
You shop has put the vehicle on its lift and hand-rotated all the wheels to verify they rotate freely, right?
Hi Stephanie:
Did you get the rubber flex hoses at each wheel replaced? As others have noted, they can (and often do) cause the symptom you’re describing. The internal layers of the hoses begin to delaminate which leads to a one-way valve effect.
Once all, the usual suspects have been ruled out, you may start looking at less likely possibilities. What if the brake switch is being activated intermittantly? Is it possible the ABS then kicks in?
Is it possible to have a mechanic start at the master cylinder rod and investigate all the possibilities on out to those little hoses and the temperature, etc… at the wheels? All the possiblities in one shot?
I know it would take some time but would that be feasible?
Thanks!