why isn't miles to brake service.changing?

[Ron07x5]

I bought a 2007 x5 at 105k in California and.drove it to.texas it.now has about 3000 more miles on it but the miles til brake service needed hasn't changed for either the front or rear at.all per.the car info. What.gives? The x5 says brakes needed.in 3900 for rear and.5000? For front. I see.records.say front was.done about 38000 ago and.rears.about 50000.ago

[Davidf]

The mileage to service is an estimate. The car has no way of monitoring the condition of the brakes other than "about to need service" and "needs servicing". I.e, the brake pads have a two stage wear sensor. So, don't worry about the mileage to service until you get a message that says you need to service the brakes.

[bmrboi2]

It also has something to do with driving style and how hard you are on your brakes. I have noticed on more aggressive driving days it says I need rear brakes in 5000 miles, more conservative days 7500. Same with the fronts. 12,000 on aggressive days and 25000 on conservative days.

[Ron07x5]

I am seeing the same exact numbers since I got the car about 3000 miles ago ... they are not changing! Both fronts and rears reported as needing service in something under 5000 miles.

So they have two wear sensors on each brake pad? One that is wearing down constantly and the other only when it must be done?

Seems I can really on what the car is telling me about the brake condition since it isn't changing. Note I also hate the no water-temp or oil pressure, no oil dip stick or transmission dip stick.

I am a computer software engineer and I do not mind the computer trying to help me, but if the system is poor and only tells me when I am failing that doesn't help me as much as .... oil 1/4 low, oil 1/2 low, oil 1 quart low ... please add a quart ... oil 2 quarts low please stop driving until adding 2 quarts. Or temp 160% and normal. temp 180 and higher then normal, temp 200 potential problem if continues, 210 this is good you in the desert, 220 you are in trouble.

Anyway issue here is about the computer reporting of future brake service ... me the engineer needs to understand what the designing engineers did and didn't do very well.

[Davidf]

No, one sensor with two wire loops molded in at different positions. The sensors only start to wear when the pads are getting close to worn out. First loop cut and you get a service due soon warning (or something along those lines). Second loop cut and you get a service due immediately warning (or something along those lines). There is no sensor that actually measure the pad wear continuously. So, the mileage to service indicator is an assumption based on average pad life as determined by BMW. I have no idea if the computer takes driving style into account and adjust the mileage estimate accordingly.

Edit: You should also know that there are two loops in the sensor, but still only a two wire sensor. When one loops gets cut (worn through), it changes the resistance of the sensor as measured by the computer. When the second loop gets cut, the circuit is then "open".

[lanbrown]

The brakes are part of CBS. CBS is Condition Based Service. So depending on the conditions )i.e. how you drive) the system will base the estimations when it views it is time for service. As previously mentioned, it really doesn't know with 100% certainty when brakes need to be serviced until the sensor tells it. Up until that point, CBS is using various factors to determine when it thinks it will be due.

Maybe you are much lighter on the brakes than the previous owner and thus the mileage is not being reduced as you are putting far less wear on them.

[Davidf]

Also, if the PO used non OEM pads, then the service indicator is completely useless as pad life is not what BMW assumes (regardless of driving style). If the pads are OEM, and it was me, the first thing I would do is yank those OEM pads out and slap in some Akebono Euro's: longer lasting, almost dust free, and less touchy brake feel.

[bmrboi2]

From what I've noticed on other BMW's I've owned the brake monitoring system is accurate to a fault. When I had 1200 miles on my fronts in my E60, I immediately yanked the front wheels, pads and rotors and replaced with Zimmerman rotors and Brembo pads. The front pads were thin on both sides which leads me to believe that the system is accurate in it's reporting. Thats the basis I am using just purely on experience. (granted the E60 is not an E70 but logic dictates that the systems are similar but with german cars that assumption doesnt hold much water)

[lanbrown]

With 1,200 miles listed by the CBS, the first part of the sensor should have been tripped. Once the sensor is tripped, I would expect that the system has a much clearer picture of pad life left. I believe the sensor is tripped when about 2,000 miles are left on the pads. The question would be, right before it tripped, did CBS state 2,000 miles or some other value?

[Ron07x5]

Originally Posted by trader4

Since it's a car he just purchased and the system is saying brakes
are estimated to have just a few thousand miles left, why not pull
a wheel front and back and have a look?

Yep it.is on my list