How accurate are the brake sensors? - BMW 3-Series (E90 E92) Forum

nycbr · 09-23-2012, 08:54 PM

The computer is telling me I have 3K left on the rear brakes. Do I need to change them now or can I wait for a warning light? I don't want to take a chance on scoring the rotors.

Thx

PS - why do the rear brakes wear out first? And any recommendations on pads with stock rotors? Thx again

mid-corner fun · 09-24-2012, 08:55 AM

Quote:

Originally Posted by nycbr

The computer is telling me I have 3K left on the rear brakes. Do I need to change them now or can I wait for a warning light? I don't want to take a chance on scoring the rotors.

Thx

PS - why do the rear brakes wear out first? And any recommendations on pads with stock rotors? Thx again

The 3K left is just an estimate based on how long it took you to to trip the first stage of the sensor. Since you have no warning light, I'm guessing you haven't tripped the 2nd stage yet. The only way to really answer that is to have the pads inspected (for remaining mm)

Rears go first because DSC uses them actively to keep you safely on the road.

Chriztofor · 09-27-2012, 08:35 PM

It is pretty accurate. I would wait until 1k to change unless you want to change it now while the weather is not bad instead of changing them in the dead of winter.

volkswackin · 09-27-2012, 08:40 PM

they arent very accurate actually...

Chriztofor · 09-27-2012, 08:59 PM

Relying on the sensor reading, I always had plenty of meat left on my pads, but it looks like people had different experiences. YMMV

Brian_TII · 09-27-2012, 11:03 PM

Mine had plenty left with both the CBS and wear sensor tripped. Once you get to that stage you'll want to replace them weather they are actually worn out or not due to how annoying all the warnings are. If I were you I'd replace them when it gets down to a few hundred miles. Any sooner is probably a waste and any later and the car will go nuts complaining.

Efthreeoh · 09-29-2012, 08:38 AM

Okay, I'll explain how the system works. First off the wear sensors are pretty accurate near the end of the pad life if the car is driven in a consistant manner (i.e. driven to work the same route each day). The brake pad wear system works in two stages. When the pads are new and the system is reset, the CBS computer uses a standard calculation to estimate the remaining pad life. The wear sensors have two stages (two loops of wire) that trigger the system to adjust the pad life estimate once the "first stage" of wear is determined, meaning the first loop of wire breaks in the sensor.

The computer assumes the car is being operated in the same manner as it was during the first amount of miles it took to break the stage one wire loop and adjusts the pad life estimate accordingly. Once the second stage loop of wire breaks, the brake pad replacement light is triggered in the gauge cluster and remains on until such time the pads and sensor are replaced. Once the pad wear replacement light illuminates, you have a few thousand miles to replace the pads. They have a few millimeters of pad material remaining.

You can safely wait until the brake pad replacement indication shows and then get the pads replaced within the next thousand miles. With BMW's system all you really need to do is wait for the replacement indicator to light and then get the pads changed. Don't sweat it.

Frosty · 10-02-2012, 10:57 PM

Quote:

Originally Posted by Efthreeoh

Okay, I'll explain how the system works. First off the wear sensors are pretty accurate near the end of the pad life if the car is driven in a consistant manner (i.e. driven to work the same route each day). The brake pad wear system works in two stages. When the pads are new and the system is reset, the CBS computer uses a standard calculation to estimate the remaining pad life. The wear sensors have two stages (two loops of wire) that trigger the system to adjust the pad life estimate once the "first stage" of wear is determined, meaning the first loop of wire breaks in the sensor.

The computer assumes the car is being operated in the same manner as it was during the first amount of miles it took to break the stage one wire loop and adjusts the pad life estimate accordingly. Once the second stage loop of wire breaks, the brake pad replacement light is triggered in the gauge cluster and remains on until such time the pads and sensor are replaced. Once the pad wear replacement light illuminates, you have a few thousand miles to replace the pads. They have a few millimeters of pad material remaining.

You can safely wait until the brake pad replacement indication shows and then get the pads replaced within the next thousand miles. With BMW's system all you really need to do is wait for the replacement indicator to light and then get the pads changed. Don't sweat it.

Thank you for explaining this

09-23-2012, 08:54 PM	#1
nycbr Private First Class Drives: 2008 328xi Join Date: Jun 2011 Location: long island new york Posts: 164 iTrader: (0)	How accurate are the brake sensors? The computer is telling me I have 3K left on the rear brakes. Do I need to change them now or can I wait for a warning light? I don't want to take a chance on scoring the rotors. Thx PS - why do the rear brakes wear out first? And any recommendations on pads with stock rotors? Thx again
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09-27-2012, 08:35 PM	#3
Chriztofor Colonel Drives: '06 325i Auto Join Date: Feb 2010 Location: Chicago Burbs Posts: 2,434 iTrader: (1)	It is pretty accurate. I would wait until 1k to change unless you want to change it now while the weather is not bad instead of changing them in the dead of winter. __________________ For most BMW problems start off by scanning your car with the BT Tool or Peake Research Tool. They contain the actual BMW codes as opposed to a generic OBII scanner. Pays for itself on the 1st scan. http://www.bavariantechnic.com/ OR http://www.peakeresearch.com/ (less expensive, but does not reset battery info)

09-27-2012, 08:59 PM	#5
Chriztofor Colonel Drives: '06 325i Auto Join Date: Feb 2010 Location: Chicago Burbs Posts: 2,434 iTrader: (1)	Relying on the sensor reading, I always had plenty of meat left on my pads, but it looks like people had different experiences. YMMV __________________ For most BMW problems start off by scanning your car with the BT Tool or Peake Research Tool. They contain the actual BMW codes as opposed to a generic OBII scanner. Pays for itself on the 1st scan. http://www.bavariantechnic.com/ OR http://www.peakeresearch.com/ (less expensive, but does not reset battery info)

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09-27-2012, 08:40 PM	#4
volkswackin Lieutenant Colonel Drives: too broke for a BMW Join Date: Jan 2008 Location: i get around.. Posts: 1,825 iTrader: (1)	they arent very accurate actually...

09-27-2012, 11:03 PM	#6
Brian_TII Private First Class Drives: 06 e90 330i 6spd Join Date: Aug 2010 Location: Atlanta, GA Posts: 191 iTrader: (0)	Mine had plenty left with both the CBS and wear sensor tripped. Once you get to that stage you'll want to replace them weather they are actually worn out or not due to how annoying all the warnings are. If I were you I'd replace them when it gets down to a few hundred miles. Any sooner is probably a waste and any later and the car will go nuts complaining.

09-29-2012, 08:38 AM	#7
Efthreeoh Captain Drives: E90 Join Date: May 2012 Location: MARLAND Posts: 878 iTrader: (0)	Okay, I'll explain how the system works. First off the wear sensors are pretty accurate near the end of the pad life if the car is driven in a consistant manner (i.e. driven to work the same route each day). The brake pad wear system works in two stages. When the pads are new and the system is reset, the CBS computer uses a standard calculation to estimate the remaining pad life. The wear sensors have two stages (two loops of wire) that trigger the system to adjust the pad life estimate once the "first stage" of wear is determined, meaning the first loop of wire breaks in the sensor. The computer assumes the car is being operated in the same manner as it was during the first amount of miles it took to break the stage one wire loop and adjusts the pad life estimate accordingly. Once the second stage loop of wire breaks, the brake pad replacement light is triggered in the gauge cluster and remains on until such time the pads and sensor are replaced. Once the pad wear replacement light illuminates, you have a few thousand miles to replace the pads. They have a few millimeters of pad material remaining. You can safely wait until the brake pad replacement indication shows and then get the pads replaced within the next thousand miles. With BMW's system all you really need to do is wait for the replacement indicator to light and then get the pads changed. Don't sweat it.