[Lotus99]

The one in the pic below, that gets installed in pads. I doubt it's what sends the signal to the computer that estimates how many more miles you can go before changing your pads, right? (The info you see in iDrive about servicing.)

I assume it lets off a squeal as the pad wears down to it? Or does your brake light go off in the dash?

How many more miles you figure you can keep driving at that point?
.

[pits200]

Once the wear sensor gets down to a certain point it completes the circuit and trips the brake light. You can drive with it as long as you want after that as long as the brake light doesn't bother you.

[Lotus99]

LOL, I guess you're being facetious with your last point... When once the light trips, I'm going to have to get on having it replaced. Just wanted to have an idea how many miles (let's say average city driving) you might have left. Not different than asking when the fuel light goes off, how many more miles can you drive. I realize brakes are a safety thing, and no one will give you a solid answer for fear, but was just hoping for a rough idea.

Sounds like one can ignore the iDrive message at least when it tells you that brakes are needed as that's just the computer's guess and you can keep going til the sensor trips, at which point you better get on it soon.

[e90pilot]

It depends. It's not much. Maybe 100 miles or less. The pads don't wear perfectly evenly especially if you're heavy footed. The sensor is located on the top of he pad so if the bottom wears first you might have only a few miles left after the light comes on. This happened to me. The car's computer measures brake pressure over time and records replacement history in order to figure out the miles remaining.

[Lotus99]

Oh dang... So it sounds like when it goes off, it's almost panic time.

Thanks for letting me know. Was thinking I could just wait til light trips, and there might be a 1000 miles of driving left or something, like how the fuel light gives you lots of time (relatively I guess) to drive and find a station.

[Laurus_CEO]

Shit, I've had the light on for a while now and keep putting it off. I keep visually checking the pads and they all have a good amount of meat on them except for the rear passenger side which has the sensor and is very worn. I better get on this ASAP before I wreck my calipers etc.

[ashmostro]

The sensors are unreliable in my experience. Visual inspections trump stupid sensors.

[Andy328i]

^^

I agree, talk about over-engineering!

Can the sensors be over-ridden? I keep buying new ones whenever one breaks due to ice, snow, rocks hitting it, etc.

[ashmostro]

Yes, they absolutely can be overridden. What you do is cut the sensor wire about 6 inches from the connector, strip the two wires enough to be able to solder them together (short circuit) and then insulate them with waterproof shrink tubing, or similar. Reset your CBS triggers and you are good to go.

It goes without saying (but it takes all kinds) that you must rely on common sense and your eyes to visually inspect pad thickness, both in front of and behind the rotors to make sure your pad thickness is in check.

My sensors had a false failure on the track from extreme heat and incorrectly warned me that my pads had worn through. I inspected and saw that the wire jacket had melted and shorted against the rim under heavy G forces. The pads were still near max thickness. I immediately did the workaround above and haven't looked back since. Good riddance.

[ashmostro]

Originally Posted by Lotus99

The one in the pic below, that gets installed in pads. I doubt it's what sends the signal to the computer that estimates how many more miles you can go before changing your pads, right? (The info you see in iDrive about servicing.)

Correct, the CBS uses mileage to "estimate" remaining wear. However the sensor only has two modes - short circuit or open circuit. When working properly, the sensor eventually gets worn through by the rotor and an open circuit forms, which tells you the pads have hit minimum thickness, regardless of what the CBS current state is.

The problem is, there are a multitude of other things that can happen to the sensor or wire leads that can give false readings, which are not only annoying but reduce your trust in the sensor, rendering the point moot, IMO.

[Andy328i]

Originally Posted by ashmostro

Correct, the CBS uses mileage to "estimate" remaining wear. However the sensor only has two modes - short circuit or open circuit. When working properly, the sensor eventually gets worn through by the rotor and an open circuit forms, which tells you the pads have hit minimum thickness, regardless of what the CBS current state is.

The problem is, there are a multitude of other things that can happen to the sensor or wire leads that can give false readings, which are not only annoying but reduce your trust in the sensor, rendering the point moot, IMO.

Exactly! I've had too many false warnings, only to take the wheel off and see a broken sensor dangling helplessly!

Too bad I ordered new sensors - I'm soldering them into oblivion this weekend!!

[Blackhawk36]

You should be fine for 12-1500 miles. I know I was.

[mweisdorfer]

I would go OEM. BMW computers are really sensitive and cranky. You will probably be ok with an after market sensor, but OEM sensors are not that much more. It's just piece of mind.

They work because the sensor becomes part of the brake pad when you install it in the middle of the pad. It sits lower then the beginning thickness of the new pad. When the pad eventually wears down to the thickness where the sensor is, the sensor gets rubbed. When this happens, the sensor sends a message to computer.