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Discussion Starter #1
Anyone has the knowledge on how the Ioniq (HEV/PHEV) brake system work in detail?

I’ve tried searching for the information without any luck. The closest I can get is the brake system on Ford Escape hybrid, but it doesn’t work quite the same as in Ioniq. I’ve also looking for information on the Niro without any luck either.
 

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Press the brake pedal, hydraulic action causes pistons to push brake pads against discs?
NO - Press the brake pedal, but not to much, and the regen will activate and slow the car, just as it does when you take your foot of the accelerator. Realise that you are not slowing fast enough and then HIT the brake pedal hard - that is when the mechanical brakes will cut in.

Ideally, you should be able to run on regen and never use the mechanical brakes - get power back in the battery for free.
 

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Discussion Starter #5
My question is.
1.What is IBAU and why the car need it?
2.How and where the assist pressure come from when ICE is not running?
3.The service manual show the procedure to reset the pressure sensor underneath the brake pedal, why does the car need a pressure sensor at the pedal? What is it for?
4.The bleeding procedure has two step. first is to bleed the fluid between IBAU and ECU, the second is to bleed at the calipers. Why do we need to bleed at the IBAU and ECU?
5.etc.
 

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Discussion Starter #7 (Edited)
OK, after looking for a while, I've got something. The break system in the Ioniq has two major component; 1) Integrate Brake Actuator Unit (IBAU) ; 2) Pressure Supply Unit (PSU) ; 3) brake lines and hoses ; 4) brake caliper ; 5) brake pads, rotors

The PSU is an electric pump that supply high-pressure brake fluid to the IBAU. It takes brake fluid from the reservoir and makes high-pressure brake fluid ready for the IBAU at all time the car is on.

IBAU is the heart and brain of the system. it senses pressure from brake pedal and figure the best possible way to slow the vehicle down. If the pedal is lightly pressed, it uses re-gen brake ; if the pedal is pressed further, it uses both the re-gen and friction. However, in the case of IBAU and/or PSU malfunction, all the force to stop the vehicle come from the brake pedal. The driver have to put more effort to slowdown the vehicle because there are no re-gen nor high-pressure brake assist from the PSU.

Because the system has brake fluid flow between IBAU and PSU, unlike the ICE car that has a simpler fluid flow from master cylinder to calipers, the bleeding process can not be completed by only bleeding at the calipers.

Because the IBAU is monitoring the pressure from the pedal and changing brake fluid change the pressure curve, so we need to reset the pressure sensor, and let the IBAU re-learn the curve, after brake fluid changed.

Bottom line. Brake fluid replacement is another task that can not be completed without GDS.
 

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OK, after looking for a while, I've got something. The break system in the Ioniq has two major component; 1) Integrate Brake Actuator Unit (IBAU) ; 2) Pressure Supply Unit (PSU) ; 3) brake lines and hoses ; 4) brake caliper ; 5) brake pads, rotors

The PSU is an electric pump that supply high-pressure brake fluid to the IBAU. It takes brake fluid from the reservoir and makes high-pressure brake fluid ready for the IBAU at all time the car is on.

IBAU is the heart and brain of the system. it senses pressure from brake pedal and figure the best possible way to slow the vehicle down. If the pedal is lightly pressed, it uses re-gen brake ; if the pedal is pressed further, it uses both the re-gen and friction. However, in the case of IBAU and/or PSU malfunction, all the force to stop the vehicle come from the brake pedal. The driver have to put more effort to slowdown the vehicle because there are no re-gen nor high-pressure brake assist from the PSU.

Because the system has brake fluid flow between IBAU and PSU, unlike the ICE car that has a simpler fluid flow from master cylinder to calipers, the bleeding process can not be completed by only bleeding at the calipers.

Because the IBAU is monitoring the pressure from the pedal and changing brake fluid change the pressure curve, so we need to reset the pressure sensor, and let the IBAU re-learn the curve, after brake fluid changed.

Bottom line. Brake fluid replacement is another task that can not be completed without GDS.
Brake fluid replacement has no bearing on the pressure activation. Brake fluid is incompressible. The action of the fluid should have no impact on the how/when of brake pressure activation, except insofar as volume in the lines may have effect.

I think you are massively overthinking cause:effect.
 

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From your description, it sounds like the bleeding process can be completed at the calipers. However, the CPU may have to be reset. Or not. Not sure why a proper fluid replacement would affect anything.
 

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2018 HEV Blue Purchased (new) end of May, 2018. Replacing (used) 2017.



The last three days, as I open driver's door, I hear a low growling sound, as if a pump were running. Lasts about 10 seconds. I thought that this (new) sound might be the fuel pump preparing to start the ICE. But walking around to rear of car, sound seemed much stronger in driver's seat location.

Ah, try, before starting car in my quiet garage, pump the brake. Yes, now I hear same sound briefly. I think I am hearing the source of the pressure for brake assist. (Vacuum or pressure, don't know. Probably air pump, replacing the function of intake manifold vacuum on older cars.

But why, after 18 k-miles would it start this routine. I'm sure it is a new sound. (I hear it with and without hearing aids active:)

Any one else out there notice this? Can it be related to snow and slush on the roads last week?Will be 52 F this week-end. Maybe it will go away although has been well above freezing in garage past few days.
Ideas to share before I make an appointment with the dealer?
TIA, ken
 

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Discussion Starter #11
2018 HEV Blue Purchased (new) end of May, 2018. Replacing (used) 2017.



The last three days, as I open driver's door, I hear a low growling sound, as if a pump were running. Lasts about 10 seconds. I thought that this (new) sound might be the fuel pump preparing to start the ICE. But walking around to rear of car, sound seemed much stronger in driver's seat location.

Ah, try, before starting car in my quiet garage, pump the brake. Yes, now I hear same sound briefly. I think I am hearing the source of the pressure for brake assist. (Vacuum or pressure, don't know. Probably air pump, replacing the function of intake manifold vacuum on older cars.

But why, after 18 k-miles would it start this routine. I'm sure it is a new sound. (I hear it with and without hearing aids active:)

Any one else out there notice this? Can it be related to snow and slush on the roads last week?Will be 52 F this week-end. Maybe it will go away although has been well above freezing in garage past few days.
Ideas to share before I make an appointment with the dealer?
TIA, ken
Many of us experienced that sound, it is from Intregrated Brake Actuator Unit (IBAU). Some of us has the IBAU replaced and the noise was gone.
 

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I had the pump replaced but I still hear it.
Not as loud as before but definitely.
I can sit in the car before I start it and repeatedly touch the brake pedal and it will run that pump for a couple of seconds.
I'm in holding pattern waiting for it to get louder or stay the same.
As I said, did not hear it for until 18 k-miles on the 2018 HEV Blue nor on the 12 k-miles on the 2017 HEV Blue.
I'm just say'n.
 

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Discussion Starter #14
I replaced my brake fluid yesterday.

If you are not trying to remove air from the system you do not need to mess with IBAU and PSU, just bleed at the calipers as an ICE car.

While reading the service manual, I've found this.
30714


The noise is from the PSU and it is normal, according to the service manual.
 
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