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Brake wear sensor not working ?
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08-21-2018, 12:00 PM | #1 |
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Brake wear sensor not working ?
Hello,
My rear brake wear sensor indicates that i have 800 miles left on my rear brakes. However, it has been 800 miles for quite a while now, and i'm pretty sure i've driven over that amount. I'm a bit concerned that the brake wear sensor is not doing its job. Is this possible ? What is the best way to manually check if I still have life left on my brakes ? I do not have any squeaking/squealing etc.
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08-21-2018, 12:19 PM | #2 |
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Pull a rear wheel and look at the pad thickness and the state of the wear sensor. There is only 1 wear sensor on the rear and I cannot remember if it is passenger or driver side. If you are down to only a couple mm of pad thickness, you probably want to change the pads before you end up wearing down to the metal pad backing a scoring the rotors (which then need to be replaced).
If you have at least 3mm of pad thickness on both inner and outer pads, you are probably in good shape for a bit. If the wear sensor has come loose, it may have been rubbing the disc and worn down quickly, while the pads are fine.
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08-21-2018, 12:44 PM | #3 |
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The sensor trips a warning (do you have one?)...it's the CBS computing the distance.....for example, when I did my 4 brakes at once, and reset, it showed front 90,000, rear 45,000. I haven't gone far maybe 3k miles, and now the fronts show 90,000, and the rears, 39,000. See how it isn't even remotely accurate?
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08-21-2018, 12:45 PM | #4 | |
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08-21-2018, 02:39 PM | #5 |
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If the brake system has been maintained correctly, then it is behaving normally. The miles remaining is just an estimate. When the pads are spent, the red parking brake light will illuminate and remain illuminated while driving (with no chime). The pad wear system is 2-stage, which means the CBS estimates wear on the pads based on a predetermind forumla until the pad wear sensor hits the first wear trigger (event). The system does not indicate to the driver that the event took place, but uses the event to better estimate the brake wear pattern of the car. However, if the car is driven differently post the 1st trigger event, then the estimate can be incorrect. An example is if the car is originally driven in the city, then later is switched to highway use. Or, if the car is sold to a new owner that drives it differently. The 2nd trigger event, which illuminates the red brake icon, is the tell that the pads are spent and need to be replaced.
My advice (from 30 years of BMW ownership) is when the pad light does come on, replace the pads and rotors as a set, along with a new sensor. |
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08-21-2018, 02:43 PM | #6 | |
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08-21-2018, 04:48 PM | #7 | |
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just to be sure, I will physically inspect the brakes.
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08-21-2018, 08:50 PM | #8 | |
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some places that come to mind that will do this: 1) Firestone 2) Pepboys 3) Big Brand Tire Any place that you take your car to get it's oil change can also provide this service for you too since they already have the car up on a lift. Just because the the CBS tells you it is low "mileage" doesn't mean it is accurate. On my second set of pads/rotors for my n54... with BMW rotors/pads/sensor from Tischer... my front brakes were saying I had 7600 miles remaining when I was at 107k miles on the clock. I just changed my pads and rotors when it was showing me I had 1800 miles remaining a couple days ago (I'm at 162,000 miles when I did it). I probably could have gone another 10,000 miles on the 2mm/3mm of pad remaining but I don't want to cut it that close. morale of the story, the CBS is nice as a dummy reminder... but the only real way to check your brakes is to pull off the wheel and visually look at the pad itself. remember, there is only ONE sensor for the front wheels and it only measures the depth of ONE side of ONE wheel as opposed to the TWO actual wheels with TWO sides of pads on each wheel. The sensor is making some assumptions that the other 3 pads are "about" the same. |
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08-21-2018, 08:55 PM | #9 | |
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08-21-2018, 09:37 PM | #10 | |
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A manual transmission can be set to "comfort", "sport", and "track" modes simply by the technique and speed at which you shift it; it doesn't need "modes", modes are for manumatics that try to behave like a real 3-pedal manual transmission. If you can money-shift it, it's a manual transmission. "Yeah, but NO ONE puts an automatic trans shift knob on a manual transmission."
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08-21-2018, 09:42 PM | #11 |
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The sensor definitely needs to be replaced as the way it's used is that it gets physically broken and that when it triggers a signal.
I think it's like a wire surrounded by rubber and when the electrical loop opens it triggers the code. |
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08-21-2018, 10:49 PM | #12 |
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Yes, it is a two stage wire... when the first stage is worn thru it triggers the yellow CBS mileage and the sensor can't be reused. Once it gets to the second stage, the red brake CBS mileage is displayed. With FCPEuro, you will never need to pay for another sensor again... so no need to ever reuse.
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08-21-2018, 10:51 PM | #13 |
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My original set of pads/rotors while under 100k miles on the car were very accurate. But on my second set it was not accurate at all on my fronts. I'm now on my third set for the fronts (still on the second set in the rears). Maybe I just got unlucky with the front set from BMW/Tischer?
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08-22-2018, 10:55 PM | #15 | |
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More info on the BMW brake sensor: https://www.e90post.com/forums/showthread.php?t=981050 Also, the yellow warning indicator doesn't come on when the sensor reaches first stage. The first stage is only a data point for the computer to be able to make a better estimate on the remaining life of the pad. A question was why the rear was showing less life than fronts. This happened with mine too, and it was accurate my rear pads were worn out before my fronts. Some claimed it is due to DSC intervening more on the rears, don't know. It could be just that the read pads have less meat to do the job than the fronts. what I know the computer estimate was very accurate on my first set of pads, both front and rear. Once the first stage is tripped the sensor is not reusable. |
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08-24-2018, 08:04 AM | #16 | |
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A manual transmission can be set to "comfort", "sport", and "track" modes simply by the technique and speed at which you shift it; it doesn't need "modes", modes are for manumatics that try to behave like a real 3-pedal manual transmission. If you can money-shift it, it's a manual transmission. "Yeah, but NO ONE puts an automatic trans shift knob on a manual transmission."
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brakes, diy, n54 335i |
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