CBS

GingerPilotGuy · 01-10-2020, 09:45 AM

Hey guys,

Curious if anyone has any technical knowledge on how the CBS works when it comes to Brake Fluid and pad-wear.

My car is now at 82k kms (51k miles), and I received a message from the CBS saying Brake Fluid is due to be changed. At only 82k kms and the car being less than three years old, it seems a bit soon to me.

I also received a message saying the rear brake pads are due. Is this due to a km threshold being reached, or are there accurate sensors that determine brake wear on the front and rear pads?

I don't mind doing them, I'm just curious if it's a necessity or not... or if BMW codes the system to have both of these changed just after the standard warranty expires?

Thanks in advance for your responses!

FaRKle! · 01-10-2020, 10:43 AM

Brake fluid is time based I believe (2yrs). For pad wear there's a sensor with electrical contacts that gets ground down by the rotor. When the contact gets ground down and an open circuit occurs it says you should change the brakes because the pad thickness for that to happen is low. Before that though the mileage countdown is modeled, and not necessarily accurate.

MacklinUSOB · 01-10-2020, 10:46 AM

If you haven't been driving the car very hard your brake fluid should still be serviceable. However, BMWs interval is two years. Some will hem and haw about following their recommendation (claiming wastefulness) but I bleed mine four times in that period to maintain for HPDE, it's all about usage.

Doing a visual inspection on the rear brakes is pretty easy, just shine a flashlight and observe the pad thickness. There is a pad sensor but it is a simple conductor, it has no bearing on the CBS system until it makes physical contact with the rotor. The lighter the use, the more likely your rear pads expire first due to electronic brake proportioning.

Billfitz · 01-10-2020, 11:30 AM

Brake fluid intervals are time based, as there's no mechanism on the car that can measure brake fluid water content. I got one of these so I wouldn't change it either too early or too late:
https://www.amazon.com/ITEQ-Liquid-T...NsaWNrPXRydWU=

Brake pads are time and condition based, though the only condition the car can detect is when a sensor trips, at which point you've got a thousand miles or less to go.

GingerPilotGuy · 01-10-2020, 01:43 PM

Quote:

Originally Posted by FaRKle!

Brake fluid is time based I believe (2yrs). For pad wear there's a sensor with electrical contacts that gets ground down by the rotor. When the contact gets ground down and an open circuit occurs it says you should change the brakes because the pad thickness for that to happen is low. Before that though the mileage countdown is modeled, and not necessarily accurate.

Thanks all for the replies. Fluid is sort of what I thought. It's not a terribly expensive thing to have done anyway. I'd rather have that done professionally since they have the systems in place to bleed to brakes better than I can at home.

As for the pads. I've been watching the kms count down for a while, so I knew the alert was coming. I don't drive the car hard nor are the pads super worn down. I wonder if it would be best to reset the pad alert and wait for another 10k kms or until the sensor trips it again...

Billfitz · 01-10-2020, 01:50 PM

Quote:

Originally Posted by GingerPilotGuy

As for the pads. I've been watching the kms count down for a while, so I knew the alert was coming.

Don't trust that. My experience:
http://f30.bimmerpost.com/forums/sho....php?t=1471617

01-10-2020, 09:45 AM	#1
GingerPilotGuy New Member 6 Rep 25 Posts Drives: 2017 328d xDrive Join Date: Jan 2018 Location: Ottawa, Canada iTrader: (0) Garage List 2017 BMW 328d [0.00]	CBS - Brake Fluid and Rear Pads Hey guys, Curious if anyone has any technical knowledge on how the CBS works when it comes to Brake Fluid and pad-wear. My car is now at 82k kms (51k miles), and I received a message from the CBS saying Brake Fluid is due to be changed. At only 82k kms and the car being less than three years old, it seems a bit soon to me. I also received a message saying the rear brake pads are due. Is this due to a km threshold being reached, or are there accurate sensors that determine brake wear on the front and rear pads? I don't mind doing them, I'm just curious if it's a necessity or not... or if BMW codes the system to have both of these changed just after the standard warranty expires? Thanks in advance for your responses!
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01-10-2020, 10:43 AM	#2
FaRKle! Brigadier General 4017 Rep 3,540 Posts Drives: 328d Wagon, M2 Comp, i4 eD35 Join Date: Sep 2016 Location: Bay Area, CA iTrader: (4) Garage List 2023 BMW i4 eDrive 35 [0.00] 2017 BMW 328dx Wagon [0.00] 2021 BMW M2 Competi ... [0.00]	Brake fluid is time based I believe (2yrs). For pad wear there's a sensor with electrical contacts that gets ground down by the rotor. When the contact gets ground down and an open circuit occurs it says you should change the brakes because the pad thickness for that to happen is low. Before that though the mileage countdown is modeled, and not necessarily accurate. __________________ -328d Wagon Build Log (with helpful reference links) -My YouTube Channel for some of the best DIYs and in depth information Please don't PM me for suspension recommendations unless interested in paid private consultations.
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01-10-2020, 10:46 AM	#3
MacklinUSOB Captain 518 Rep 891 Posts Drives: f30 328i 6MT Sport Join Date: Jan 2017 Location: Connecticut iTrader: (0)	If you haven't been driving the car very hard your brake fluid should still be serviceable. However, BMWs interval is two years. Some will hem and haw about following their recommendation (claiming wastefulness) but I bleed mine four times in that period to maintain for HPDE, it's all about usage. Doing a visual inspection on the rear brakes is pretty easy, just shine a flashlight and observe the pad thickness. There is a pad sensor but it is a simple conductor, it has no bearing on the CBS system until it makes physical contact with the rotor. The lighter the use, the more likely your rear pads expire first due to electronic brake proportioning. __________________ 328i RWD \| MW on CRed Slick Top \| 6MT \| BM3 \| MPE \| GPlus FMIC \| CSF Radiator \| Millway Street Camber Plates & Monoballs \| KW V2 6k/18k Swift Springs \| F80 LCA/TS \| SPL Bump Steer Kit \| APEX SM-10 \| R-S4 \| DS2500 \| RBF600 \| SS Lines \| Past: E36 328is & E38 740i Last edited by MacklinUSOB; 01-10-2020 at 10:54 AM..
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01-10-2020, 11:30 AM	#4
Billfitz Lieutenant General 8245 Rep 16,088 Posts Drives: '15 328iX GT Join Date: Jan 2015 Location: New Hampshire iTrader: (0)	Brake fluid intervals are time based, as there's no mechanism on the car that can measure brake fluid water content. I got one of these so I wouldn't change it either too early or too late: https://www.amazon.com/ITEQ-Liquid-T...NsaWNrPXRydWU= Brake pads are time and condition based, though the only condition the car can detect is when a sensor trips, at which point you've got a thousand miles or less to go.
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