Brakes Engaged on Their Own (no pedal) to Full Stop. (1 Viewer)

[iron_giant]

Looking for some guidance on where to start troubleshooting and share our story because things could have been a lot worse.

Rig: 2013, 120,000 Miles. Lifted, Bumpers, carrying weight. Excellent Maintenance.

Wife was driving to work this morning on a country road at about 45 mph w/ no cruise control. She passed a vehicle and the brakes suddenly engaged to full stop. She said quite a few dash lights came on all at once. As soon as the vehicle was at a complete stop, brakes released and dash lights turned off. She immediately turned around and drove home with no issue. It has rained a little (in Northern California) but roads were fairly dry. Obviously she was a little shaken up and we will park the rig until I can troubleshoot a little further and bring to local dealers attention.

Has anyone had something similar happen? Were you able to diagnose?

My immediate thoughts are traction control and ABS systems. I will read codes, verify wiring and report back.

Thanks,
David

 

[Sandroad]

My first guess would be water in the wrong place inside shorting out something related to emergency braking or cruise control (even though no engaged). Windshield leaking? Sunroof drains clogged? Water in the dash or under the sills? Etc.

 

[goldwater58]

Pre collision system malfunction? Did you have your windshield replaced recently? May need an ADAS recalibration.

 

[linuxgod]

Pre collision system malfunction? Did you have your windshield replaced recently? May need an ADAS recalibration.

PCS would be my thought as well, though in my experience PCS doesn’t apply the brakes it just preloads them so when you tap them they will lock the F up. Apparently Mercedes discovered most rear end collisions were because humans don’t brake hard enough at first. I’ve had PCS engage when I’m passing a truck a bit too closely and let off the gas, or if a flatbed or semi wanders into my lane, so a car passing the other way is feasible as it’s just the radar detecting the distance to an object being closed rapidly. If she tapped the brakes at all this might make sense. And it does light up the dash

 

[bloc]

PCS would be my thought as well, though in my experience PCS doesn’t apply the brakes it just preloads them so when you tap them they will lock the F up. Apparently Mercedes discovered most rear end collisions were because humans don’t brake hard enough at first. I’ve had PCS engage when I’m passing a truck a bit too closely and let off the gas, or if a flatbed or semi wanders into my lane, so a car passing the other way is feasible as it’s just the radar detecting the distance to an object being closed rapidly. If she tapped the brakes at all this might make sense. And it does light up the dash

This.

And @goldwater58 08-15 don’t have the cameras which means no windshield calibration. I would say radar only but some LXs and possibly early LC200s didn’t even have that..

 

[Sandroad]

Here’s a thread on the PCS operation in a ‘13.

Are the active safety features any good in the 200? Found out today

I like safe vehicles, and I have long believed Land Cruisers to be some of the safest on the road. Relatively recent technology has enabled robust active safety features to help avoid or reduce the severity of accidents, but I've always been a little skeptical of how well safety tech in the 200...

forum.ih8mud.com

There doesn’t seem to be any threads about braking without touching the pedal. Looks like maybe a unique instance?

 

[gasman4u]

Here’s a thread on the PCS operation in a ‘13.

Are the active safety features any good in the 200? Found out today

I like safe vehicles, and I have long believed Land Cruisers to be some of the safest on the road. Relatively recent technology has enabled robust active safety features to help avoid or reduce the severity of accidents, but I've always been a little skeptical of how well safety tech in the 200...

forum.ih8mud.com

There doesn’t seem to be any threads about braking without touching the pedal. Looks like maybe a unique instance?

I can attest to SOME braking without touching the pedal (no complete stop however) likely due to PCS. This most approximates situations that others have experienced with the PCS in similar siutations while driving. I didn't pay attention to the lights on the dash other than the "BRAKE" flashing light in the middle of the information screen of my 2021.

 

[bloc]

@iron_giant the FSM lists a detailed procedure for leveling the radar antenna.. and the vast majority of us don't do that. After things like suspension modifications it may be just as important as the better-known but still under-performed zero-point calibration. Could be a contributing factor?

 

[linuxgod]

@iron_giant the FSM lists a detailed procedure for leveling the radar antenna.. and the vast majority of us don't do that. After things like suspension modifications it may be just as important as the better-known but still under-performed zero-point calibration. Could be a contributing factor?

Good point.

When I was towing earlier this year coming back from Canada I got a PCS error a couple times. Radar sensor was clear - no snow, washed off any bugs. It would go away after a few minutes but every few hours would return for the rest of the trip. Since I parked the trailer it hasn't come back. My hunch was that my rear was squatting a bit too much and the PCS sensor was aimed too high.

 

[mobi-arc]

PCS can kick in when maneuvering around vehicles at speed....sent my dog flying once when I was in control but the system disagreed and slammed on the brakes.

 

[iron_giant]

Thanks for the great information. I will start digging in and post up. I used to spend a lot of time on this site and was a much more active contributor. It seems like ages ago. Glad to know the spirit is still alive!

David