ABS System Randomly Fighting Acceleration

[Weizsla]

We have a '21 3.5TT Advanced+ with 59,868 miles. Last November, a couple weeks ago and tonight we've had this problem. We're driving at highway speeds and start to feel a little shake in the steering wheel. It begins to get worse and the vehicle feels like it's getting resistance to acceleration. It seems to get worse as we slow down, perhaps because the brakes can grip better on a slower turning wheel. With my foot off the breaks and approaching a stoplight, the car doesn't coast to a stop, it STOPS! It also has a slight break squeak at the end as it lurches to a full stop. When we start again at the slower speed it seems ok again, but there is a bad break smell coming from the wheels. No faults show on the dash, but I'm wondering if it's an ABS issue. Brought it to the Genesis/Hyundai dealer where we bought it. No faults and couldn't get the problem to happen again while test driving it. Another time we took it to the local stand-alone Genesis dealer a little further away. They couldn't figure it out either. Thankfully this time my wife was able to film it with her phone while I was driving. I'll call the Genesis dealer again in the morning and this time show them the video. Anyone else having this kind of trouble?

 

[JohnnyBs25Prestige3.5T]

Have the brake calipers checked for binding or bad pads. Dragging brakes will generate heat which will make the symptoms worse the more the car is driven. Excessive heat will warp rotors and cause shaking. 60K miles is a good time to have the brakes checked out just on general principle.

 

[mikec]

Does it exhibit these symptoms right at the start of a drive - i.e. when the engine and brakes are stone-cold? Or does it happen after using the brakes a few times? Or randomly after the engine is warmed up?

If it happens even when things are stone-cold, I would strongly suspect a dragging brake. Rust in a brake piston can jam the brakes on one wheel. Typically what happens is the jam lets the piston move when you apply the brakes - the pressure in the brake fluid is enough to move the piston - but when you release the brakes the excess friction/jam keeps the piston from backing off... ergo dragging brakes on that wheel which creates heat. The bolts that support a brake caliper are supposed to let the caliper body slide back and forth as the brakes are applied: the piston pushes on the brake rotor while also pushing its half of the caliper away from the rotor, this pulls the other caliper half into the brake rotor.so both brake pads theoretically share the braking load. But if either bolt or anything in the slide mechanism is rusted or cruddy the excess friction causes one side to not release properly resulting in brake drag on one of the two brake pads at that wheel.

If the brakes are perfectly normal on the first drive of the day (brakes and engine are cold) but starts getting bad once things warm up then I would suspect insufficient brake pedal freeplay or a mis-adjusted brake master cylinder. As the engine bay heats up, metal parts and the brake fluid thermally expand a little. There is supposed to be a little "useless" pedal travel - the freeplay - that makes sure the pistons in the master cylinder are released far enough back to let brake fluid trapped in the brake lines to backflow into the brake fluid reservoirs. If the freeplay is insufficient (i.e. little brake pedal travel is needed to actually apply the brakes) then the brake fluid is trapped... and thermal expansion of things will create pressure in the brake lines, applying the brakes at the wheels. With the vehicle OFF and stone-cold, use a fingertip to lightly press the brake pedal. It should move at least a quarter inch/8 millimeters before any significant resistance is felt. Typically you have light resistance - the spring on the brake pedal itself - and then it hits a mild "stop" or bump and the resistance increases a little - that is when the brake pedal pushrod actually contacts the guts of the master cylinder... that quarter-inch travel is the freeplay.

Do you have one of those hand-held temperature guns like many stores were using to measure your forehead temp during the Covid-19 timeframe? After a drive, use it to measure the temperature of the brake rotors and compare one front brake to its twin on the other side, one rear brake to its twin on the other side. A large side-to-side mismatch is proof of a dragging brake... or of the following situation:

The other thing that can cause odd steering wheel sensations is the stability control going stupid - thinking the vehicle is spinning out so it applies brakes to just one wheel to counter the skid. A brain-fried "lane keeping assist" might tug at the steering wheel but would not cause dragging brakes... just random tugs on the steering wheel.

mike c.

 

[J&J GV80]

We have a '21 3.5TT Advanced+ with 59,868 miles. Last November, a couple weeks ago and tonight we've had this problem. We're driving at highway speeds and start to feel a little shake in the steering wheel. It begins to get worse and the vehicle feels like it's getting resistance to acceleration. It seems to get worse as we slow down, perhaps because the brakes can grip better on a slower turning wheel. With my foot off the breaks and approaching a stoplight, the car doesn't coast to a stop, it STOPS! It also has a slight break squeak at the end as it lurches to a full stop. When we start again at the slower speed it seems ok again, but there is a bad break smell coming from the wheels. No faults show on the dash, but I'm wondering if it's an ABS issue. Brought it to the Genesis/Hyundai dealer where we bought it. No faults and couldn't get the problem to happen again while test driving it. Another time we took it to the local stand-alone Genesis dealer a little further away. They couldn't figure it out either. Thankfully this time my wife was able to film it with her phone while I was driving. I'll call the Genesis dealer again in the morning and this time show them the video. Anyone else having this kind of trouble?

My wife has the same model as you (‘21 3.5TT Advanced) and has had this same issue occur 3 times with 2 of them happening on a busy highway. Do you have an update on how this was resolved? Did the video help with showing something to the dealer?