2019 Silverado LT Z71 brakes straight to floor at S/U?

[bigdoug42]

Went to start the truck today, and like the title says brake pedal went straight to the floor as I went to press the start button. Let brake pedal back up, press start button, yellow light around button came on, then put foot on brake pedal again, this time brake pedal was again firm and truck started normally. No MIL light. Have had both brake updates done. No further trouble today. Anyone else experienced this?

[ILSilverado]

Scary for all of us. I would get it in ASAP.

[topgear1224]

Went to start the truck today, and like the title says brake pedal went straight to the floor as I went to press the start button. Let brake pedal back up, press start button, yellow light around button came on, then put foot on brake pedal again, this time brake pedal was again firm and truck started normally. No MIL light. Have had both brake updates done. No further trouble today. Anyone else experienced this?

I know it's really scary but it's actually normal behavior for a hydroboost system. Especially an electronically-controlled one.

so here's what's actually happening when your trucks off the motor is not boosting the brakes so you get a nice firm pedal, well if you're actually applying downward Force to the pedal when you turn on the truck that motor begins to spin and boost the brakes which then makes the pedal travel downward.

now it will not do this if the truck is not off for a certain amount of time since every time you shut off the truck it will cycle the brake system after preset amount of time. so if it does this and you shut the truck back off and then turn it back on it will not drop the pedal to the floor. If you shut the truck off come back in half an hour put your foot on the brake push down on the brake and hit the start button it'll go to the floor.

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[bigdoug42]

Thank you for that explanation, I had no idea about that. It was just, you know, the whole brake pedal to the floor thing, lol.

[Thomcat]

21 hours ago, topgear1224 said:

I know it's really scary but it's actually normal behavior for a hydroboost system. Especially an electronically-controlled one.

so here's what's actually happening when your trucks off the motor is not boosting the brakes so you get a nice firm pedal, well if you're actually applying downward Force to the pedal when you turn on the truck that motor begins to spin and boost the brakes which then makes the pedal travel downward.

now it will not do this if the truck is not off for a certain amount of time since every time you shut off the truck it will cycle the brake system after preset amount of time. so if it does this and you shut the truck back off and then turn it back on it will not drop the pedal to the floor. If you shut the truck off come back in half an hour put your foot on the brake push down on the brake and hit the start button it'll go to the floor.

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59 minutes ago, bigdoug42 said:

Thank you for that explanation, I had no idea about that. It was just, you know, the whole brake pedal to the floor thing, lol.

The 2019 Silverado/Sierra (the real 2019s not the 2018 carryover LD version) does not use a hydroboost system.....just lift the hood and look.......no more power brake booster or vacuum lines........and no more power steering pump. This is a new ZF fly by wire IBC setup.

 

https://gmauthority.com/blog/2018/10/zf-highlights-brake-by-wire-system-in-silverado-sierra/

 

As described in the above your foot pedal does not apply pressure to the hydraulic system....a motor screw ball applies pressure depending upon position of the pedal. I have no idea what a pedal to the floor means in an IBC system, but mine has never done it. First thing I would check would be stored codes in the ECU/BCU and if none I'd still get to the dealer ASAP for an explanation.

 

Same goes for relying on the lightweight save the planet "emergency" brake button for a stop in case of main brake failure.....that damn thing is also controlled by a motor and no longer with decent brake shoes on a steel drum/disc assembly......the shoes are now thin and designed for parking brake purpose only and the drum portion of the rear drum/rotor assembly is aluminum.

Edited April 18, 2020 by Thomcat

[topgear1224]

The 2019 Silverado/Sierra (the real 2019s not the 2018 carryover LD version) does not use a hydroboost system.....just lift the hood and look.......no more power brake booster or vacuum lines........and no more power steering pump. This is a new ZF fly by wire IBC setup.
 
https://gmauthority.com/blog/2018/10/zf-highlights-brake-by-wire-system-in-silverado-sierra/
 
As described in the above your foot pedal does not apply pressure to the hydraulic system....a motor screw ball applies pressure depending upon position of the pedal. I have no idea what a pedal to the floor means in an IBC system, but mine has never done it. First thing I would check would be stored codes in the ECU/BCU and if none I'd still get to the dealer ASAP for an explanation.
 
Same goes for relying on the lightweight save the planet "emergency" brake button for a stop in case of main brake failure.....that damn thing is also controlled by a motor and no longer with decent brake shoes on a steel drum/disc assembly......the shoes are now thin and designed for parking brake purpose only and the drum portion of the rear drum/rotor assembly is aluminum.

Okay fair enough. I was just at the dealership (fighting with them over a different brake issue) and literally made them get into five different trucks with me every single one of those trucks did that.

Hop into a truck that's been off,
stand on the brake pedal,
Hit the start button,
Pedal drops,
Release pedal,
Reapply pedal-pedal feels normal.
Release pedal,
Shut truck off,
Push on brake,
Restart truck,
Pedal doesn't move.

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[newdude]

On 4/17/2020 at 12:20 PM, topgear1224 said:

I know it's really scary but it's actually normal behavior for a hydroboost system. Especially an electronically-controlled one.

so here's what's actually happening when your trucks off the motor is not boosting the brakes so you get a nice firm pedal, well if you're actually applying downward Force to the pedal when you turn on the truck that motor begins to spin and boost the brakes which then makes the pedal travel downward.

now it will not do this if the truck is not off for a certain amount of time since every time you shut off the truck it will cycle the brake system after preset amount of time. so if it does this and you shut the truck back off and then turn it back on it will not drop the pedal to the floor. If you shut the truck off come back in half an hour put your foot on the brake push down on the brake and hit the start button it'll go to the floor.

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The 1/2 tons don't have hydroboost brakes.  That is a 2500/3500 thing.  Hydroboost is using the hydraulic power steering system to provide brake assist.

The new 1/2 tons are e-boost.  The brake assist is provided electronically via a motor.  No vacuum, no nothing.  In the event of assist failure, the brake pedal still can apply mechanical (the pedal) over hydraulic (brake fluid) braking force, but no assist.    

Edited April 18, 2020 by newdude

[topgear1224]

 
The 1/2 tons don't have hydroboost brakes.  That is a 2500/3500 thing.  Hydroboost is using the hydraulic power steering system to provide brake assist.

The new 1/2 tons are e-boost.  The brake assist is provided electronically via a motor.  No vacuum, no nothing.  In the event of assist failure, the brake pedal still can apply mechanical (the pedal) over hydraulic (brake fluid) braking force, but no assist.    

That sounds like a hydroboost system that just uses an electric motor instead of a power steering pump.

I'm just now finding out that there's possibly no pedal connection whatsoever to anything?????

so does that mean in theory if I'm driving down the highway and my battery was to fall out of the truck, and the truck stalls. pushing on the brake wouldn't do anything!?!??!!!??

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[newdude]

1 hour ago, topgear1224 said:

That sounds like a hydroboost system that just uses an electric motor instead of a power steering pump.

I'm just now finding out that there's possibly no pedal connection whatsoever to anything?????

so does that mean in theory if I'm driving down the highway and my battery was to fall out of the truck, and the truck stalls. pushing on the brake wouldn't do anything!?!??!!!??

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Its not hydroboost or anything like it.  Hydroboost uses the power steering to provide assist.  

 

The pedal is connected still to the brakes.  If you loose assist, you are still pushing the pedal and then sending brake fluid to the calipers.  You would have no assist is all.  This works the same as if you lost vacuum assist.  

 

 

Quote

 

Brake Assist System Description and Operation

System Component Description

Note: The above graphic may not be an exact representation for every vehicle configuration.

The brake assist system is an electro - hydraulic brake booster that replaces a vacuum booster including its vacuum supply. The brake booster unit takes the driver applied brake demand and transforms this into an amplified brake pressure and does not rely on vacuum to function. The brake booster unit is designed to operate together with an electronic stability control module which is normally responsible for ABS, traction control and stability control.

The master cylinder and power brake booster unit consists of a brake master cylinder reservoir (1), an electronic brake booster control module (2), pedal coupling unit/pushrod, and the brake master cylinder (3) with integrated brake pressure modulator valve.

System Operation

Brake system input force is multiplied by the brake pedal and transferred by the pedal pushrod to the hydraulic brake master cylinder. Effort required to apply the brake system is reduced by the electronic brake booster.

Shutdown Test

The brake master cylinder performs a self-test 2 minutes after ignition off. The self-test consists of an internal hydraulic test of the brake master cylinder and an external hydraulic compliance test and hydraulic leak test of the brake lines and calipers. The brake master cylinder will take the appropriate actions based on the test results at the next startup. The self-test will not run again until the vehicle has been driven 0.804 Km (0.5 mile), 40.23 kph (25 mph) minimum.

Brake Assist System Description and Operation

Brake Assist Operating Mode	Description	Vehicle Braking Behavior	Vehicle Speed limited to 100kph	Red Brake Telltale	DIC	Other Displays
Full Brake Assist	- Normal hydraulic brake assist. - Brake pedal travel and force (pressure) measured. - Pedal feel indicates the relation of the pedal travel to the pedal force. - Brake system applies brake pressure to the wheels to achieve deceleration that makes driver effort comfortable.	- Pedal feel: Normal (force to travel of brake pedal). - Brake pedal effort to decel: Normal. - Pedal Travel restricted to 80 mm due to pedal simulator.	No	No	None	None
Full Brake Assist with warning	- Normal hydraulic brake assist. - Driver warned with DIC message only of detected failure. - There may be a small brake assist or pedal feel degradation depending on if/where the air is in the system or what component is overheated.	- Pedal feel: Normal. - Brake pedal effort to deceleration: Normal. - Pedal Travel restricted to 80 mm due to pedal simulator.	No	No	Service Brake Assist	None
Reduced Brake Assist	- Normal hydraulic brake assist available - Driver warned with DIC message but due to nature of failure, engineering determined more warning needed. - Brake assist gain reduced in a noticeable fashion at low pedal travel (not alarming). - Full braking available as pedal is depressed further.	- Pedal feel: Normal - Brake Pedal effort to decel: More effort required for low decel values (noticeable).  Full braking capability for increased effort. - Pedal Travel restricted to 80 mm due to pedal simulator.	No	No	Service Brake Assist	None
Reduced Brake Assist	- Normal hydraulic brake assist on 2 wheels. - Performed when brake system detects and isolates a leak in one of the two brake circuits.	- Pedal feel: Normal. - Brake pedal effort to deceleration: Same deceleration requires double the effort. Can only achieve 50% deceleration. - Vehicle will pull slightly to the side with the Front Brake active. - Pedal Travel restricted to 80 mm due to pedal simulator.	Yes	Yes	Brake System Failure 100 kph Top Speed Low Brake Fluid (Potentially)	ABS, ESC, and Engine Telltales Service Traction and ESC DIC Vehicle Speed Limited display from ECM
Two Wheel Brake Assist	- Normal hydraulic brake assist on 2 wheels. - Performed when brake system detects and isolates a leak in one of the two brake circuits.	- Pedal feel: Normal. - Brake pedal effort to deceleration: Same deceleration requires double the effort. Can only achieve 50% deceleration. - Vehicle will pull slightly to the side with the Front Brake active. - Pedal Travel restricted to 80 mm due to pedal simulator.	Yes	Yes	Brake System Failure 100 kph Top Speed Low Brake Fluid (Potentially)	ABS, ESC, and Engine Telltales Service Traction and ESC DIC Vehicle Speed Limited display from ECM
No Brake Assist with Electric Park Brake Assist	- Hydraulic brake assist not available. - Brake System uses Electric Park Brake to assist driver braking.	- Pedal feel: Slightly stiffer than normal. - Brake pedal effort to deceleration: Onset of braking is similar but more force required to achieve same deceleration compared with Full Brake Assist. - Minimal non linearities in deceleration due to use of Electric Park Brake. - Pedal travel's almost to the floor with high effort.	Yes	Yes	Brake System Failure 100 kph Top Speed	ABS, ESC, and Engine Telltales Service Traction and ESC DIC Vehicle Speed Limited display from ECM
No Brake Assist (Push Thru)	- No hydraulic or Electric Park brake assist available. - Driver pedal  force distributes equal pressure to all 4 wheels	- Pedal feel: Slightly softer than normal. - Brake pedal effort to deceleration: Onset of braking requires more travel AND more force required to achieve same deceleration compared with No Brake Assist with Electric Park Brake Assist. - Pedal Travel's almost to the floor with high effort.	Yes	Yes	Brake System Failure 100 kph Top Speed (Not displayed for full power loss or critical micro failures)	ABS, ESC, and Engine Telltales Service Traction and ESC DIC Vehicle Speed Limited display from ECM
Two Wheel No Brake Assist (2 Wheel Push Thru)	- Hydraulic brake assist not available. - Brake system  applies and releases Electric Park Brake proportional to driver pedal force to assist driver braking.	- Pedal feel: Significantly softer than normal. - Brake Pedal effort to deceleration: Onset of braking requires more travel AND more force required to achieve same deceleration compared with No Brake Assist. - Vehicle will pull slightly to the side with the Front Brake active. - Pedal Travel's almost to the floor with high effort.	Yes	Yes	Brake System Failure 100 kph Top Speed	ABS, ESC, and Engine Telltales Service Traction and ESC DIC Vehicle Speed Limited display from ECM
Brake Fade Detected Level 1	- Normal hydraulic brake assist available. - Brakes system estimates brake temps of 500 - 600 deg C. - Driver warned with DIC display. - Brake assist gain reduced in a noticeable fashion at low pedal travel (not alarming). - If brake assist gain was not changed, the brake over-temp would not be as noticeable as on vacuum brake system.	- Pedal feel: Normal - Brake Pedal effort to deceleration: Not significantly changed - Pedal Travel restricted to 80 mm due to pedal simulator.	No	No	Reduce Braking to Avoid Overheating	None
Brake Fade Detected Level 2	- Same as Level 1 but brake temperature 700 - 900 deg C. - Degradation in brake lining output may become noticeable. - Degradation in response time may become noticeable. - Far better performance than a vacuum system.	- Pedal feel: Normal. - Brake Pedal effort to deceleration: Increase in effort required based on temperature of brake which decreases brake pad output. - Pedal Travel restricted to 80 mm due to pedal simulator.	Yes	Yes	Brakes Overheated Service Now	None

 

 

[topgear1224]

No hydroboost does not use the power steering it uses the hydraulic pressure from the power steering pump.

it seems like the new system uses an electronic motor to create hydraulic assist is that not correct?

The same way in a hydroboost system it would use a hydraulic pump (power steer pump) to provide power assist. I beleiev that is why you are saying?

So is the pedal directly connected to a hydraulic piston that has brake fluid in it or no??

Do you have a direct connection from the brake pedal to the master cylinder, to apply pressure through the brake lines to the caliper through the pad to the rotor?

"According to a Wards Auto report last Thursday, the system works with a pedal simulator. Fluid in the master cylinder is displaced to an accumulator and the system measures pedal travel. A motor with a ball screw then pushes a plunger to deliver hydraulic fluid to the wheels."

Basically will it stop with no electric power at all?

I'm just trying to get to the bottom of this because I'm trying to figure out whether or not MY truck is trying to kill me or not

https://www.gm-trucks.com/forums/topic/237772-a-new-and-different-brake-issue/&share_tid=237772&share_fid=33003&share_type=t&link_source=app




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[bigdoug42]

Thank you for that explanation, I had no idea about that. It was just, you know, the whole brake pedal to the floor thing, lol. 

25 minutes ago, topgear1224 said:

No hydroboost does not use the power steering it uses the hydraulic pressure from the power steering pump.

it seems like the new system uses an electronic motor to create hydraulic assist is that not correct?

The same way in a hydroboost system it would use a hydraulic pump (power steer pump) to provide power assist. I beleiev that is why you are saying?

So is the pedal directly connected to a hydraulic piston that has brake fluid in it or no??

Do you have a direct connection from the brake pedal to the master cylinder, to apply pressure through the brake lines to the caliper through the pad to the rotor?

"According to a Wards Auto report last Thursday, the system works with a pedal simulator. Fluid in the master cylinder is displaced to an accumulator and the system measures pedal travel. A motor with a ball screw then pushes a plunger to deliver hydraulic fluid to the wheels."

Basically will it stop with no electric power at all?

I'm just trying to get to the bottom of this because I'm trying to figure out whether or not MY truck is trying to kill me or not

https://www.gm-trucks.com/forums/topic/237772-a-new-and-different-brake-issue/&share_tid=237772&share_fid=33003&share_type=t&link_source=app




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Ok, as the original poster I am now more confused than ever.

[topgear1224]

Thank you for that explanation, I had no idea about that. It was just, you know, the whole brake pedal to the floor thing, lol. 
Ok, as the original poster I am now more confused than ever.

Same

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[topgear1224]

Anyone have the technical document from ZF for this particular brake module?? I'm explicitly looking for how the system functions.

The idea that it uses an independent reservoir that has a sensor to determine brake pedal travel, to them electronically communicate that to an electronic brake actuator makes sense. especially for the kind of issue that I'm having and the kind of issues that others have. and aligns with what people are saying that it is "brake by wire".

but again if it's being translated electronically then there is no Fail-Safe. if you, for instance, lose all electric power to the truck while driving.

I know OEMs do a lot of stupid things but I can't really see GM doing that after their whole 2500 hydroboost fiasco a couple years ago. (Where customers claim that ABS engagement meant that they couldn't turn the steering wheel)

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[topgear1224]

this was as close as i could find.......

 

http://www.freepatentsonline.com/20170361824.pdf 

 

anyone confirm this is the system used on our trucks people were quoted saying it was a ZF system

[Mikedfw]

Okay fair enough. I was just at the dealership (fighting with them over a different brake issue) and literally made them get into five different trucks with me every single one of those trucks did that.

Hop into a truck that's been off,
stand on the brake pedal,
Hit the start button,
Pedal drops,
Release pedal,
Reapply pedal-pedal feels normal.
Release pedal,
Shut truck off,
Push on brake,
Restart truck,
Pedal doesn't move.

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Mine does this in that the pedal drops, but not to the floor. It doesn't feel like it is completely released.

If it goes all the way to the floor I would have them check it out personally.

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