Cruise Control Braking Problem

Carl911 · August 16, 2011

I had my cruise control turned on and set at 50 mph.

My left foot was resting on the foot rest and my right on the floor near the accelerator.

Eventually I started to catch up to slow moving traffic in front so applied the brakes.

The brake pedal went to the floor and in my panic I pushed the accelerator thinking I had pushed the wrong pedal by accident.

I then turned off the cruise and re applied the brake pedal and the brakes worked.

Fortunately I was not close enough to anything to have an accident.

Now I immediately thought that I must of accidentally pushed the clutch instead of the brake but I can't see how as this would mean taking my right foot over to the extreme left side which I doubt I could of done.

I'm pretty convinced that I did indeed push the brakes and they sunk to the floor.

I'm a little concerned.

I tried to make this occur again several times but everything worked fine after that one time.

My question is, is there Any reported issues of something like this happening as if it was a brake issue I could of had a nasty accident.

Carl

steve2006 · August 16, 2011

Seems strange that one.

Total brake failure is virtually unknown with dual circuit systems and I don't remember any recalls for this problem or other reported incidents.

I assume you have since the incident checked the fluid level and looked for any evidence of leaks on the braking system?

As you say it is unlikely but you may have hit the clutch pedal in error and providing it never happens again you will probably have to assume this is what happened.

With cruise on I tend to keep my right foot just hovering above the brake pedal so I know where I am with the foot in relation to the pedal, no clutch to consider on mine though.

I find I cannot completely relax in cruise mode and need to feel some control so never put my right foot flat on the floor completely away from the pedals.

Matus · August 16, 2011

few years ago here was a guy who had problem with brakes on IS.

knitware · August 16, 2011

Sounds like a scary experience!

If I see traffic build up in front while I'm using cruise I just turn the cruise off, I don't brake unless an emergency.

Not sure at all what your problem was but I doubt that you hit the clutch, sounds a bit odd.

Carl911 · August 16, 2011

Sounds like a scary experience!

If I see traffic build up in front while I'm using cruise I just turn the cruise off, I don't brake unless an emergency.

Not sure at all what your problem was but I doubt that you hit the clutch, sounds a bit odd.

All fluids look fine and no sign of any leaks.

I will have to put it down to comfortable ride plus good music & cruise control = too relaxed and not in full control.

Will reposition the feet in future.

Carl

Baldchap · August 16, 2011

If there's fluid in the system and your brake servo isn't losing pressure then you cannot have hit the brake pedal.

Next time you are in the car, turn off the engine and pump the brake pedal. It should become firmer to the point where you can barely push it. If it doesn't you may have a servo leak (which leaks air so is hard to detect - perhaps get a friend to listen for hissing in the engine bay whilst you do this)...

Simon_D · August 16, 2011

Had you driven over some bumps just before this? I haven't experienced this in a car but on bikes if you hit some bumps or have a bit of a tank slapper the pads/pistons can move away from the disk and the first brake application will bring the lever back to the bars. They are fine once they've been pumped back up.

Baldchap · August 17, 2011

Had you driven over some bumps just before this? I haven't experienced this in a car but on bikes if you hit some bumps or have a bit of a tank slapper the pads/pistons can move away from the disk and the first brake application will bring the lever back to the bars. They are fine once they've been pumped back up.

Never experienced this (thankfully) - what do you ride?

Simon_D · August 17, 2011

For the last 10 years or so mainly Buells with the odd KTM here and there.

Matus · August 17, 2011

myself ktm too (and gsx-r for the racetrack) :)

Cue · September 14, 2011

This happened to me once!!!!

But then I woke up from that sweatful dream and was relieved....

Anyway more to the point, and more irrelevant, I keep my finger on the cruise control switch, period. I trust the clutch and brake to release CC but I much prefer cancelling out the CC with the lever.

Ducatiman · September 16, 2011

Sort of off thread a little but I had an experience yesterday that I I'll not do again. Whilst in stop/start heavy motorway traffic I was sort of messing around with my phone when I didn't notice the van in front of me brake hard. The radar system kicked in and the car started braking before I did - freaky to say the least.

Skidspan · September 22, 2011

Just read this interesting thread about alleged brake failure while panic braking while in cruise control mode. From what you describe I'm certain you did apply the clutch pedal instead of the brake pedal for an instance. I know this sounds unbelivable, but I can confirm I did exactly the same thing when I first got my Lexus IS 220D. I was tipping along at a good pace in cruise mode, both feet resting on the floor when approching a really slow moving vehicle. I paniced jumped on the brake pedal (I thought) it sank to the floor.....PANIC I quickly lifted my foot and down again I hit the solid brake pedal and avoided the rear ender. Immediatly I thought the brakes failed. I have looked at this over and over and tried simulating the condition again. I can confirm in a panic situation the movement of your right foot ( when not in the natural position on the accelerator pedal)can over react and hit the clutch pedal an inch beside the brake pedal. The pedal set up is quite compact in the Lexus. Now while in cruise I rest my foot over the accelerator as it's natural to move quickly from accellerator to the brake as your right foot movement is trained that way since you started driving, natural movement!

I hope to have explained my my experience and shed some light on this topic.

Skidspan

Paul Craft · February 28, 2014

Not sure if this is what happened to me yesterday, unfortunately the HGV in front was harder than my car, will let you know when Lexus give a technical report.

On my Mercedes (sorry) if you hit the Clutch or the Brake the Cruise switched off, should or does Lexus do the same?

is200 Newbie · March 1, 2014

Yes - touching the brake pedal will turn the cruise off - nasty smash ... reparable?

Paul Craft · July 12, 2014

Report back from Lexus is "user error", they must think I would drive my car on a motorway into a HGV for fun

Car now back as good as new, but have my doubts in letting the car doing the thinking for me, all controls now set to manual

Very disappointed with Head office and my Dealer for not helping, would buy Lexus again but back up service poor

samres82 · May 29, 2016

On 8/16/2011 at 10:18 AM, Carl911 said:

I had my cruise control turned on and set at 50 mph.

My left foot was resting on the foot rest and my right on the floor near the accelerator.

Eventually I started to catch up to slow moving traffic in front so applied the brakes.

The brake pedal went to the floor and in my panic I pushed the accelerator thinking I had pushed the wrong pedal by accident.

I then turned off the cruise and re applied the brake pedal and the brakes worked.

Fortunately I was not close enough to anything to have an accident.

Now I immediately thought that I must of accidentally pushed the clutch instead of the brake but I can't see how as this would mean taking my right foot over to the extreme left side which I doubt I could of done.

I'm pretty convinced that I did indeed push the brakes and they sunk to the floor.

I'm a little concerned.

I tried to make this occur again several times but everything worked fine after that one time.

My question is, is there Any reported issues of something like this happening as if it was a brake issue I could of had a nasty accident.

Carl

Yesterday, on my way home to Berkshire on A 303 I've experience the same problem, but with more serious consequence, had the car IS 220d model crushed into a roadside pylon.

Was on cruise control at the same 50 mph speed as you (what a strange coincidence?!) when approaching a slower moving queue slightly hit the brake to adjust the speed to the traffic ahead when I had the surprise to realize that it was not working, tried several times to hardly hit the brake pedal but no sign of slowing. In panic I forgot about the hand brake that would have helped me to stop the car, eventually tried to shift to a lower gear and as a result while sliding through the narrow corridor of ongoing and oncoming traffic, eventually scratching an old laddies car and hitting the next one in the right rear corner I saw a gap and turned the steering sharp left into the roadside line of bushes. Ultimately the car crushed approximately at the same speed speed I was cruising before into an electricity pylon in the middle of those bushes. What a dreadful experience, but lucky nobody was injured, except me a little. All 4 front airbags deployed (thank God those did not fail anyways). That maybe saved my life, I realize now, because, as I said, the car did not slow an inch while I was hitting the brakes, maybe just a little from the impact with the car driving in front of me right before I found that bloody pylon.

Now I am still in kind of shock and really cannot figure it out what happened then, because no warning light on dashboard concerning ABS or barking, the braking fluid is alright. Seemed to me more like an electronic issue at the moment. I am really out of my spirit. Those cars are not supposed to behave like that.

johnatg · May 30, 2016

That's bad luck, to say the least - pretty dreadful experience.

I wonder if there's any possibility that these experiences described over several years could be due to a problem with the brake servo or its vacuum supply. When cruising at a steady 50mph there isn't much manifold vacuum and if there's a leak (even a very slight one) there could be no vacuum left in the servo. But diesels have a vacuum pump to keep the vacuum up (or down!) so I'm not all sure about that diagnosis. It wouldn't actually stop the brakes from working, but they would need much heavier pedal pressure than normal to have any effect.

Can't see how it can be electronic - the brakes are not 'fly-by-wire' - they operate hydraulically and if you press the brake pedal you de facto apply pressure to the caliper pistons and pads - even if the ABS system wasn't working