[lordbmw]

I was under the impression that it would warn me with an icon in the dash.

[Vivek.]

Yes

[R3dLeader]

Also a good idea to visually check the pad thickness and rotor condition. It's pretty easy.

[E92inNC]

You can always look at the outside pad thickness to know when you’re getting close.

[tcphoto]

You have brake sensors on each axle, I received a warning on my iDrive that I had about 600 miles left on pads.

[lordbmw]

Ok good. Brakes are squeeking a bit. No warning yet.

[ctuna]

It's better to physically check them .
Yes the wear sensor will go open when they get down to almost nothing.
But it's a good idea to stay ahead of it.

[TunafishE93]

Visual inspection is the only guarantee. Unless you know that the sensors are there dont rely on them. Alot of people bypass this including me.

And the pads i have doesnt have the squeak bar like regular pads so cant go by noise either

[Efthreeoh]

Originally Posted by lordbmw

Ok good. Brakes are squeeking a bit. No warning yet.

The E9X brakes have no physical pad wear device that makes a warning sound by contacting the rotor (i.e. tuning fork)
BMW has been using their sensor-based pad wear monitor system since the early 1980's. It works well when maintained correctly. It's failed me once in nearly 950,000 miles of driving several BMWs, and that instance was on my E90 when BMW wiped my software clean and reinstalled the entire software in the car in 2012, which removed the 1st trigger event for the front brakes.

While physical measuring the pads is a good idea, it's a PIA unless you have the measuring caliper (measurement tool) that measures pad thickness. But my experience is you can use the pad wear system with high confidence and high reliability.

My 2 cents.

[gbalthrop]

As I understand the E9x warning systems, you actually have TWO different warnings IF the current pads & sensors were properly installed:

1) There is a "Pad Wear Sensor" installed in the Inboard brake pad on the Left-Front brake caliper, and the Right-Rear caliper. That Wear Sensor is designed to "wear-down" in thickness along with the pad in which it is mounted. 3mm pad friction material thickness (NOT including thickness of steel "backing plate") is the minimum pad thickness for safety inspection purposes in VA and probably MOST states.

The Pad Wear Sensor is tested by the DSC Module to which it is connected by two wires. When the Pad/Sensor thickness is worn down to 3mm thick, the sensor goes "Open-Circuit" and the Brake Warning light comes on. That light does NOT tell you WHICH Sensor (LF or RR) has worn through & become Open-Circuit. At 3mm pad thickness you still have proper braking and NO metal-to-metal contact between Disc/Rotor and steel pad backing plate.

2) There is "Condition Based Service", CBS, which will give you a "Car-on-Lift"/ Service warning Icon on Instrument Cluster, IF the CALCULATED life of the pads on either front or rear has elapsed, based on current mileage, and mileage WHEN the resistance change for particular sensor occurred. That CBS-based calculation is done because the resistance (measured by DSC Module) changes when HALF of the sensor thickness has been worn away. The CBS Calculation DOES vary between Front & Rear.

Some people re-use old Pad Wear Sensors when they change brake pads, and simply use a paper-clip or other "Bridge" in the Sensor Socket to Reset the CBS. If the sensor is parially-worn, this defeats the CBS Calculation. Reprogramming the DSC would do the same, but you STILL should have Warning #1, Sensor Open-circuit, UNLESS you permanently wire the two Sensor wires into "Closed-circuit".

ANYONE with a different understanding of HOW the system actually works, please advise, WITH cites to ISTA, Bentley, or other reliable source. I'll attach ISTA sensor diagram to my next post in this thread.
George

[gbalthrop]

Pad Wear Sensor ISTA Wiring Diagram attached, 3/2007 328xi. Other E9x Models SHOULD be Same.
George

[TunafishE93]

I do the pinky test, put your pinky in there to feel the gap between pad frame and rotor. This is wise to do when cars been sitting over night. Plus i have five spoke 19" so easy access though the wheels. I can see this not working with other wheels though.

[Efthreeoh]

Originally Posted by gbalthrop

As I understand the E9x warning systems, you actually have TWO different warnings IF the current pads & sensors were properly installed:

1) There is a "Pad Wear Sensor" installed in the Inboard brake pad on the Left-Front brake caliper, and the Right-Rear caliper. That Wear Sensor is designed to "wear-down" in thickness along with the pad in which it is mounted. 3mm pad friction material thickness (NOT including thickness of steel "backing plate") is the minimum pad thickness for safety inspection purposes in VA and probably MOST states.

The Pad Wear Sensor is tested by the DSC Module to which it is connected by two wires. When the Pad/Sensor thickness is worn down to 3mm thick, the sensor goes "Open-Circuit" and the Brake Warning light comes on. That light does NOT tell you WHICH Sensor (LF or RR) has worn through & become Open-Circuit. At 3mm pad thickness you still have proper braking and NO metal-to-metal contact between Disc/Rotor and steel pad backing plate.

2) There is "Condition Based Service", CBS, which will give you a "Car-on-Lift"/ Service warning Icon on Instrument Cluster, IF the CALCULATED life of the pads on either front or rear has elapsed, based on current mileage, and mileage WHEN the resistance change for particular sensor occurred. That CBS-based calculation is done because the resistance (measured by DSC Module) changes when HALF of the sensor thickness has been worn away. The CBS Calculation DOES vary between Front & Rear.

Some people re-use old Pad Wear Sensors when they change brake pads, and simply use a paper-clip or other "Bridge" in the Sensor Socket to Reset the CBS. If the sensor is parially-worn, this defeats the CBS Calculation. Reprogramming the DSC would do the same, but you STILL should have Warning #1, Sensor Open-circuit, UNLESS you permanently wire the two Sensor wires into "Closed-circuit".

ANYONE with a different understanding of HOW the system actually works, please advise, WITH cites to ISTA, Bentley, or other reliable source. I'll attach ISTA sensor diagram to my next post in this thread.
George

George, (2) is the correct answer for US Market E9X. The sensor is dual stage, where Stage 1 provides actual wear data based on braking use. Stage 2 is the 3MM open circuit condition that triggers the notification in the gauge cluster. Stage 1 allows the CBS to develop a prediction of remaining pad life based on actual use data. If that data remains in the CBS control module, when the sensor is replaced and the CBS is reset, the CBS gives an estimated pad life in miles based on the collected wear data. The CBS shows pad life and spent-pad status by front or rear axle.