[tcphoto]

Why isn't there an ignore option on this forum? These new members with no manners have no place here.

[Tambohamilton]

There is, in your user CP...

[Efthreeoh]

Originally Posted by Tunafish

As I was corrected these sensors are not new... You say to do it right does this mean that 95% of the cars on the road are wrong for not having these sensors?
So they should install these sensors if they don't have them? You have these sensor on all your vehicles? If not does that mean that you yourself dont actually fix these issues?
And yes ten dollars a piece is a lot of money for an party hat trick. I stand by my statement, if you actually work on your car, theses sensors are a waste of money.

You are showing a bit of ignorance on the subject of brake pad wear sensors. A lot of cars for many decades have used an audible pad wear sensor. It's called a tuning fork indicator. It is a metal ribbon folded over and affixed to the brake pad. The short leading edge of the folded ribbon eventually contacts the surface of the rotor when the brake pad reaches its service limit. Once the leading edge contacts the rotor, it vibrates the ribbon, which acts like a tuning fork and vibrates loudly at a high pitch (sound).

So other than BMW using an electronic version of the same idea, a pad wear sensor, most cars have had some sort of device to notify the driver the brakes need servicing for as long as disc brakes have been standard equipment.

But please continue banging your head about it. It's kind of foolish to own a vehicle that has a well designed safety device that helps drivers keep their cars in safe operating condition by ignoring it because the owner is not smart enough to educate himself on the device he is trying to service.

[Efthreeoh]

Originally Posted by hassmaschine

yes, I do have these sensors on all of my vehicles (3 BMWs of varying vintage), and yes, they all work because they are inexpensive, easy to replace, and a good way to know when the brakes need it.

You mean that archaic E30 has pad wear sensors?!

[gbalthrop]

Ah! The joys of "Polarization" in the "Modern/Trump Era" (NOT "ERA")

Since we are 27+ posts DEEP into this thread, and OP is the ONLY one who has posted any actual "Documents" or "Evidence" (his two photos in Post #2), here is a link (ACTUALLY to this Forum ) which discusses the way the CBS system, Brake Pad Wear Sensors, and Warning Lights ACTUALLY work:
https://www.e90post.com/forums/showp...6&postcount=29

Then there's the Pad Wear Sensor wiring diagram from TIS/ISTA attached to next post, Front Left Wear Sensor B16a. Connector View of X18145, the two-socket connector to which the Wear Sensor is attached is shown on the Right Side of the ScreenPrint. The Second attached TIS/ISTA document screenprint is the Installation Location of the Wear Sensor (B16a) and the Chassis Connector (X18145) to which the Sensor connects.

The post linked above does NOT state HOW to Reset CBS & Warning Light when Sensor is NOT fully worn (Open Circuit). That HAS been described by others (I have NOT had to replace wear sensors, so I'm relying on posts by others such as PhaseP who HAVE tested and posted their findings.

IF you have a Sensor which has NOT gone "Open Circuit", with resistance essentially INFINITE, or MUCH Greater than 470 Ohms, you CAN "Reset" the warning Light or CBS by disconnecting the Sensor from X18145, putting a paper clip or bent wire in BOTH sockets of the chassis connector (to "Short" or complete the circuit as a new Sensor would), and THEN you can Reset. AFTER Reset, remove the paper clip/jumper, and plug in the Old Sensor.

The other "Feature" of the system is lost when you do that however, as you will NOT get reliable "Mileage until Pad Replacement" readout from CBS, as it can't calculate the mileage between NEW pads (~ 0 resistance) and Stage 1 or mid-life resistance of 470 ohms. It WILL Light Pad Wear Sensor warning light when resistance goes to Open circuit when pads & Sensor are BOTH worn to 3mm remaining pad thickness.

OR, you can just short the wiring and wait until you hear the "metal-on-metal" screech of pad backing plate scoring the disc, and THEN replace PADS & DISCS.

What you choose to do or NOT do is YOUR CHOICE. My only goal is to try to correctly understand HOW the system works. So if anyone has a DIFFERENT understanding of Warning Light & CBS function, please advise AND cite authority or source of "Facts".

Tambo/F30: It MAY be a "Fool's Errand" to try to teach the finer points of the "English Language" to "Americanese" speakers.

Thanks,
George

[gbalthrop]

Brake/Break Pad Wear Sensor wiring diagram, Connector View & Installation Location

3/2007 build date 328xi E91 with N52KP Engine:

[gbalthrop]

Brake/Break Pad Wear Sensor wiring diagram, Connector View & Installation Location

3/2007 build date 328xi E91 with N52KP Engine:

George

[gbalthrop]

Hopefully LEGIBLE SSP this time.

George

[Tambohamilton]

Originally Posted by gbalthrop

Tambo/F30: It MAY be a "Fool's Errand" to try to teach the finer points of the "English Language" to "Americanese" speakers.

Thanks,
George

Great info as ever, George. I really don't care who can/can't spell, and I'm acutely aware that dyslexia is very real... But I will confess to having rather a lot of fun in jumping on a passing spelling/grammar bandwagon

I guess my potentially useful contribution to the thread is to advise that the padwear sensors are kept wherever possible, for the same reasons I'd always recommend leaving stability control on full-nanny mode; the sensors may sometimes throw up annoying false positives, but for that one time in a million that they save your (and/or someone else's) bacon, it's worth it.

Referring to the original post, the wear sensor is, as already pointed out, part worn. As George has explained in rather more technical terms, that will prevent the fault from being reset. You can fool it into allowing the reset using the paperclip method, which is grand until the replacement arrives and you can restore full functionality.

[Efthreeoh]

Originally Posted by gbalthrop

Ah! The joys of "Polarization" in the "Modern/Trump Era" (NOT "ERA")

Since we are 27+ posts DEEP into this thread, and OP is the ONLY one who has posted any actual "Documents" or "Evidence" (his two photos in Post #2), here is a link (ACTUALLY to this Forum ) which discusses the way the CBS system, Brake Pad Wear Sensors, and Warning Lights ACTUALLY work:
https://www.e90post.com/forums/showp...6&postcount=29
.

OR, you can just short the wiring and wait until you hear the "metal-on-metal" screech of pad backing plate scoring the disc, and THEN replace PADS & DISCS.

What you choose to do or NOT do is YOUR CHOICE. My only goal is to try to correctly understand HOW the system works. So if anyone has a DIFFERENT understanding of Warning Light & CBS function, please advise AND cite authority or source of "Facts".

Tambo/F30: It MAY be a "Fool's Errand" to try to teach the finer points of the "English Language" to "Americanese" speakers.

Thanks,
George

George, thanks for posting this level of detail. Me and several other members have posted similar information on how the brake pad wear system works numerous times on this from over the past 14 years or so. I have on several occasions counseled members on why the remaining pad life mileage seem incongruent with their observed pad thickness when the inspect the brakes. Explaining that from a fresh set of pads with a new pad sensor and a proper reset of the CBS, the CBS uses a predetermined algorithm to estimate the pad life until the 1st stage of the sensor is triggered (worn through). And that once the CBS determines an actual wear rate for the pads ( dependent on how the car is driven), any change in driving behavior, past the 1st stage trigger event, and effect the observed pad thickness vs. the ESTIMATED pad life in miles CALCULATED, by the CBS.

The problem is the Moderators do not take time to post some of these very informative posts, like yours made here, as "stickies" so they are easily found by members. The case here seems to be the OP didn't bother to investigate how the system works to solve his problem on his own. If Hass and I point that out, it is only to drive a level of being self-sufficient. You know, in Biblical terms... "teach a man to fish".

What is interesting is I'm in the middle of replacing the rear brakes on my E90 for the 4th time. I'm glad you found the post about the electrical resistance of the sensor because I was looking for it last week. I couldn't remember the number for the resistance (470 Ohms). The reason is at my last VA safety inspection in March, my guy I take my cars to said the rear brakes were in need of replacement. he showed me how thin the pads were, I as usual said "I'm waiting for the pad notification to come on." He's not a Bimmer shop, but does know BMWs have the pad warning notification. Anyway, I have been expecting a pad notification all summer, but it has yet to appear. BUT in the meantime, the left rear speed sensor went bad, throwing the ABS, (red)"BRAKE", DTC, Christmas tree trifecta. So what I'm trying to determine is if the Trifecta obfuscates the (red) "BRAKE" brake pad warning notification. I've looked at the pad sensor and it looks to be still intact for the second stage. I need to measure it electrically. So thanks.

And BTW, I think the intermittent speed sensor was the cause of my mysterious engine power hiccups from a few months ago if you remember...

[Efthreeoh]

Originally Posted by Tambohamilton

Great info as ever, George. I really don't care who can/can't spell, and I'm acutely aware that dyslexia is very real... But I will confess to having rather a lot of fun in jumping on a passing spelling/grammar bandwagon

I guess my potentially useful contribution to the thread is to advise that the padwear sensors are kept wherever possible, for the same reasons I'd always recommend leaving stability control on full-nanny mode; the sensors may sometimes throw up annoying false positives, but for that one time in a million that they save your (and/or someone else's) bacon, it's worth it.

Referring to the original post, the wear sensor is, as already pointed out, part worn. As George has explained in rather more technical terms, that will prevent the fault from being reset. You can fool it into allowing the reset using the paperclip method, which is grand until the replacement arrives and you can restore full functionality.

I kind of got annoyed with the break vs. brake usage after Hass pointed it out and the OP gave him shit about it. It's not a spelling error, but rather a grammar issue related to use of a noun vs. a verb.

[Efthreeoh]

Originally Posted by Efthreeoh

True, but BMW has been using brake pad wear sensors for over 40 years, yet the disc brake was introduced to the mass-produced automobile in the mid 1950s and didn't become somewhat commonplace until the mid 1960s. So of the 50 or so years disc brakes have been commonly found as standard equipment on automobiles, over 80% of that time, BMW has been utilizing the pad-wear sensor as a safety device.

or...

So of the 50 or so years disk breaks have been commonly found as standard equipment on automobiles, over 80 percent of that time, BMW has been utilizing the pad-where censor as a safety device.

Being the curious type that I am, and now at my home computer, using realoem.com, I investigated when BMW started using brake pad wear sensors (break pad where censors). I thought BMW first started using them on the 1980's era E28 and E30. But actually the E21 (first 3-series) has pad wear sensors, as does the E12 (first 5-series). That takes the date of first use of electronic pad wear sensors by BMW back to 1972.

1972...

Let that sink in.

[falconey]

Most brake pads produced nowadays have wear indicators that will audibly inform you to replace if you don't happen to pay attention to your pad wear via visual inspection.

[gbalthrop]

Originally Posted by Efthreeoh

... from a fresh set of pads with a new pad sensor and a proper reset of the CBS, the CBS uses a predetermined algorithm to estimate the pad life until the 1st stage of the sensor is triggered (worn through). And that once the CBS determines an actual wear rate for the pads (dependent on how the car is driven), any change in driving behavior, past the 1st stage trigger event, and effect the observed pad thickness vs. the ESTIMATED pad life in miles CALCULATED, by the CBS...

glad you found the post about the electrical resistance of the sensor because I was looking for it last week. I couldn't remember the number for the resistance (470 Ohms)... the left rear speed sensor went bad, throwing the ABS, (red)"BRAKE", DTC, Christmas tree trifecta. So what I'm trying to determine is if the Trifecta obfuscates the (red) "BRAKE" brake pad warning notification. I've looked at the pad sensor and it looks to be still intact for the second stage. I need to measure it electrically...

Attached is a ScreenPrint from ISTA/TIS showing the portion of "Sensor System" which relates to the two Brake Pad Wear Sensors attached to the DSC Module. Note the "Inverted Goalpost" configuration of the two wires in the Sensor "wear material". I have NO personal knowledge of the manufacturing process for these sensors, how accurate the diagram may be, or the resistance/ conductivity of the Sensor material in which the wires are imbedded. However, based upon that diagram, here is my SWAG related to HOW the sensor works:

1) The Sensor material has a relatively uniform "resistance" per unit length/distance (mm) between wires embedded in sensor. If one were to put DMM Probes 1mm, 2 mm, 4 mm apart on sensor material and record the different Ohm readings, this could be confirmed.

2) Apparently PhaseP measured the resistance of a sensor after the wires were the full distance apart (50%+ worn), and the "lateral" wires had been worn away, and measured 470 ohms.

3) What is NOT clear to me, based upon the attached diagram, is HOW there could be ZERO resistance with a new sensor. Perhaps the wires are touching or nearly so in the new sensor? Perhaps the wires are slanted and are farther apart as the sensor wears?? Perhaps the diagram is ONLY an approximation, graphic representation, or even "artist's rendering" of an actual sensor???

3b) What is even LESS clear to me from the diagram: WHAT causes the Sensor resistance to go "open circuit" or nearly so when pad thickness has decreased to 3mm? The diagram seems to be suggesting that the "mid-point" is where the wires run horizontally, and maximum separation of wires occurs when the horizontal wires are worn away. WHAT happens after that causing "open circuit"? Is there a non-conductive layer of plastic/ epoxy?

4) Strictly from the point of view of a "curious engineer wanna-be", it would be interesting to know actual resistance of a sensor at each of the three stages (New, Mid, Warning Light Triggered), and ALSO HOW that change in resistance is actually caused. My theories (confused ramblings ;-) above may be entirely incorrect, as I have never even inspected such a sensor, let alone measured its resistance at the three stages.

I'm NOT sure if BMW myth/Web Legend is correct about all the algorithms & Module Calculations. The CBS "remaining mileage on Front/Rear brakes MAY be nothing more than a calculation based upon (1) mileage at reset, (2) the resistance reading of Front Sensor and Rear Sensor, and (3) Mileage when "mid-point resistance" is recorded (separately for Front & Rear). I have NOT personally measured resistance on EITHER of my sensors (will do that next time I have a wheel off), so don't know if the exact numbers provided by PhaseP in his post are applicable to ALL, or what the variation may be.

The "Principle", if there actually IS such a thing anymore ;0 appears to be correct however. The principle would appear to be: (a) little resistance (approximated by "closed circuit" when Sensor is new; (b) resistance in the range of 450 - 500 Ohms when Sensor is "half-worn"; (c) large resistance (approaching infinite resistance) when Sensor is "fully worn to 3mm or less pad thickness.

Actual Resistance measurements welcome. Alternate theories also welcome as mine are merely guesses based upon the diagram attached. For those who wonder: "Why are you even taking the time to worry about this"? Perhaps you have a point about just shorting the two wires.

George

[Efthreeoh]

Originally Posted by gbalthrop

Attached is a ScreenPrint from ISTA/TIS showing the portion of "Sensor System" which relates to the two Brake Pad Wear Sensors attached to the DSC Module. Note the "Inverted Goalpost" configuration of the two wires in the Sensor "wear material". I have NO personal knowledge of the manufacturing process for these sensors, how accurate the diagram may be, or the resistance/ conductivity of the Sensor material in which the wires are imbedded. However, based upon that diagram, here is my SWAG related to HOW the sensor works:

1) The Sensor material has a relatively uniform "resistance" per unit length/distance (mm) between wires embedded in sensor. If one were to put DMM Probes 1mm, 2 mm, 4 mm apart on sensor material and record the different Ohm readings, this could be confirmed.

2) Apparently PhaseP measured the resistance of a sensor after the wires were the full distance apart (50%+ worn), and the "lateral" wires had been worn away, and measured 470 ohms.

3) What is NOT clear to me, based upon the attached diagram, is HOW there could be ZERO resistance with a new sensor. Perhaps the wires are touching or nearly so in the new sensor? Perhaps the wires are slanted and are farther apart as the sensor wears?? Perhaps the diagram is ONLY an approximation, graphic representation, or even "artist's rendering" of an actual sensor???

3b) What is even LESS clear to me from the diagram: WHAT causes the Sensor resistance to go "open circuit" or nearly so when pad thickness has decreased to 3mm? The diagram seems to be suggesting that the "mid-point" is where the wires run horizontally, and maximum separation of wires occurs when the horizontal wires are worn away. WHAT happens after that causing "open circuit"? Is there a non-conductive layer of plastic/ epoxy?

4) Strictly from the point of view of a "curious engineer wanna-be", it would be interesting to know actual resistance of a sensor at each of the three stages (New, Mid, Warning Light Triggered), and ALSO HOW that change in resistance is actually caused. My theories (confused ramblings ;-) above may be entirely incorrect, as I have never even inspected such a sensor, let alone measured its resistance at the three stages.

I'm NOT sure if BMW myth/Web Legend is correct about all the algorithms & Module Calculations. The CBS "remaining mileage on Front/Rear brakes MAY be nothing more than a calculation based upon (1) mileage at reset, (2) the resistance reading of Front Sensor and Rear Sensor, and (3) Mileage when "mid-point resistance" is recorded (separately for Front & Rear). I have NOT personally measured resistance on EITHER of my sensors (will do that next time I have a wheel off), so don't know if the exact numbers provided by PhaseP in his post are applicable to ALL, or what the variation may be.

The "Principle", if there actually IS such a thing anymore ;0 appears to be correct however. The principle would appear to be: (a) little resistance (approximated by "closed circuit" when Sensor is new; (b) resistance in the range of 450 - 500 Ohms when Sensor is "half-worn"; (c) large resistance (approaching infinite resistance) when Sensor is "fully worn to 3mm or less pad thickness.

Actual Resistance measurements welcome. Alternate theories also welcome as mine are merely guesses based upon the diagram attached. For those who wonder: "Why are you even taking the time to worry about this"? Perhaps you have a point about just shorting the two wires.

George

So I took a close look at the old, worn rear brake pad sensor yesterday. I don't think the sensor was triggered through the 2nd-stage (i.e. an open circuit). Interestingly the metal "wire" imbedded in the plastic is actually a small oval, about 3MM by 1.5MM (I'll measure it today). So maybe based on your theory, the size of the embedded oval is reduced in thickness over time as it contacts the rotor face and the resistance changes. But I would think environmental factors such as water and road salts, would make it difficult for the CBS ECU to capture a good reading of the changing resistance of the circuit. Unfortunately my clumsy hands let the wire harness to rip from the sensor head, so electrical measurement of the sensor will be difficult.

The situation with my rear brakes, where my safety inspector believed the brakes were near spent, was a factor of the outside pads wore faster than the inside pads (piston side). As we all know, the piston-side pad is the one that holds the wear sensor. Perhaps the brake grease I use is inadequate to keep the pads well lubed and from sticking in place on the carrier. The outside pad on the left rear brake took some effort to dislodge yesterday; it was gummed-up in-place.

The new sensor has a small "bump" in the plastic face, which I have always assumed was the first stage of the sensor, which wears quickly to get a measurement of pad wear rate as the "first stage" wear event. I think the algorithm takes in to account brake force (deacceleration) measured by the g-sensor in the console, number times the brakes are applied, average speed the car is driven over time and some baseline of expected wear. If I was an engineer, that's how I'd write the algorithm. The fist stage trigger is obviously used to get real-world data for the wear rate based on how the car is driven (i.e. used). There is a lot of data the various ECUs measure and log; insurance companies like to have it...

[lowrydr310]

Originally Posted by falconey

Most brake pads produced nowadays have wear indicators that will audibly inform you to replace if you don't happen to pay attention to your pad wear via visual inspection.

Except for the E90 brake pads, which use an electronic sensor.

The only audible indicator you'll get from the E90 is when the pads are worn completely and the backing plate starts to contact the rotor.

[xBr0k3n]

Originally Posted by gbalthrop

...

The post linked above does NOT state HOW to Reset CBS & Warning Light when Sensor is NOT fully worn (Open Circuit). That HAS been described by others (I have NOT had to replace wear sensors, so I'm relying on posts by others such as PhaseP who HAVE tested and posted their findings.

IF you have a Sensor which has NOT gone "Open Circuit", with resistance essentially INFINITE, or MUCH Greater than 470 Ohms, you CAN "Reset" the warning Light or CBS by disconnecting the Sensor from X18145, putting a paper clip or bent wire in BOTH sockets of the chassis connector (to "Short" or complete the circuit as a new Sensor would), and THEN you can Reset. AFTER Reset, remove the paper clip/jumper, and plug in the Old Sensor.

...

Thank you for this! My car has the sensors tied to the inner arch, on the front, and the rear arm as I have after market brakes. I replaced all pads on the front about a year ago, reset the warning no issue, then once I replaced the rears and reset its now telling me I need to replace all my pads and will not reset.

I'll give this a bash later as I have just fixed my ABS pump so I am in need of running the INPA/ISTA bleeding procedure on each corner.

[Pavlo335]

Sorry to revive a dead thread but I’m looking for some help. I did my front brakes about a month ago and when I went to replace the sensor, the plastic housing was so brittle it broke into a bunch of tiny pieces when I tried to unclip it. I realize I should have been more gentle. I can’t get the brake warning light on the dash to go away without replacing the sensor, but I can’t get the damn sensor unclipped now as all the plastic broken and every time I try I just break it more. I’m not too worried about the sensor functioning properly as I can keep an eye on the status of the pads, but I need to get that dash light to go away. I know theres a way to bypass the sensor but I’d rather replace the sensor if possible than cut the wires. Any advice here would be appreciated. Later tonight when I can get on my computer I will upload a picture of the mangled plastic sensor housing so you can see what I’m dealing with.

[Efthreeoh]

Originally Posted by Pavlo335

Sorry to revive a dead thread but I’m looking for some help. I did my front brakes about a month ago and when I went to replace the sensor, the plastic housing was so brittle it broke into a bunch of tiny pieces when I tried to unclip it. I realize I should have been more gentle. I can’t get the brake warning light on the dash to go away without replacing the sensor, but I can’t get the damn sensor unclipped now as all the plastic broken and every time I try I just break it more. I’m not too worried about the sensor functioning properly as I can keep an eye on the status of the pads, but I need to get that dash light to go away. I know theres a way to bypass the sensor but I’d rather replace the sensor if possible than cut the wires. Any advice here would be appreciated. Later tonight when I can get on my computer I will upload a picture of the mangled plastic sensor housing so you can see what I’m dealing with.

The sensor is a consumable item; it gets spent (i.e. used up) as the brake pads wear down. To reset the light on the gauge cluster, you must install a new pad wear sensor; all of that is explained in this thread. The new pad has a u-shaped cup in the backing plate where the new sensor clips in.

All you need to do is buy a new pad wear sensor and and clip it into the new pad (the inner pad that is on the piston-side of the caliper - driver's side of the car). Then plug it into the connector inside the plastic box hung on the fenderwell.

[oVeRdOsE.]

depends where you live too. If its like where I live, and drive in winter nordic , lot of salt and calcium, the probability state that the sensor will break before the pad need to be replaced. all my 3 cars got issue with that, all are bypassed.

I cut just near the L shaped sensor, twist the cable and use glued shrink wrap. Then tywrap.

as a car guy I keep my eye on all my stuff, so brake are checked at least 3 time /yr.

Also I do mostly highway, so even if the sensor told me to change my pad , I still have enough material for 2 years, so no way I will run the car with a warning for 2 years , annoying af.

changed my rear pad on my daaily audi in 2014, I still have around 8-9mm thickness.

[Pavlo335]

Originally Posted by Efthreeoh

The sensor is a consumable item; it gets spent (i.e. used up) as the brake pads wear down. To reset the light on the gauge cluster, you must install a new pad wear sensor; all of that is explained in this thread. The new pad has a u-shaped cup in the backing plate where the new sensor clips in.

All you need to do is buy a new pad wear sensor and and clip it into the new pad (the inner pad that is on the piston-side of the caliper - driver's side of the car). Then plug it into the connector inside the plastic box hung on the fenderwell.

I understand the sensor is a consumable item. If you had read my comment correctly I bought a new sensor and planned on replacing it but the plastic piece (the male part) that slides into the female plastic piece of the sensor had crumbled into pieces therefore making it impossible to unclip the sensor and replace it. I ended up just clipping the line before the sensor and soldering the two wires together to bypass it. I keep a good eye on my brake pads anyway so the sensor was basically useless to me.

[Pavlo335]

Originally Posted by oVeRdOsE.

depends where you live too. If its like where I live, and drive in winter nordic , lot of salt and calcium, the probability state that the sensor will break before the pad need to be replaced. all my 3 cars got issue with that, all are bypassed.

I cut just near the L shaped sensor, twist the cable and use glued shrink wrap. Then tywrap.

as a car guy I keep my eye on all my stuff, so brake are checked at least 3 time /yr.

Also I do mostly highway, so even if the sensor told me to change my pad , I still have enough material for 2 years, so no way I will run the car with a warning for 2 years , annoying af.

changed my rear pad on my daaily audi in 2014, I still have around 8-9mm thickness.

Yeah I’m on long island so the winters pretty harsh on the car and the plastic piece that the sensor plugs into had become so brittle that it crumbled into pieces. I ended up doing the same thing except I cut the line before the plastic, soldered the wires together and crimped it. Problem solved no more annoying brake light on the dash.