>

Service Info - onboard computer. Howzat work then?

S

strugglinauthor

Member
I've had the old 'red car on a ramp' come up on the dashboard and having checked the code in the owner's manual, it appears to be telling me that the brake pads are worn. A visual inspection shows me that this is probaby correct: the rear ones are considerably slimmer than the fronts!

The thing is, when I bring up the Service Info option and step through the items, it shows my rear brake pads as needing attention in 12,000 miles. I'm trying to understand how the Condition Based Service algorithm updates this info to make it reflect the real world? It would have made a lot more sense if, when I stepped through, it was showing 500 or 1000 miles.

I asked this of the BMW garage and the answer was not to pay too much attention to it and to bring the car in for an inspection. I guess that's what I'll do, but I'm trying to understand the purpose of the service info option if it seems so out of date.

Just idle curiosity but does anyone understand/use it? :?
 
The brake pad wear sensor has two contact points. When the first is worn to, it starts measuring, when the second is worn it can work out how many miles left on pads at the wear rate its experiencing. (different pads/driving style different wear rates).
I think that's how it works having replaced pads and seen close up the wear sensor.
So all warnings are a bit of guess work as you may use the brakes less/more aggressively after the measurement period.

Say if the contact points are 1mm apart and it measures 20k miles for them both to register then it assumes a 5mm pad will be safe for another 60k. With 1mm left.
If that makes any sense.
 
Thanks flybobbie and yes - that makes sense to me. Still can't see how it all ties in with the service info though, which blithely believes the brake pads are good for 000s more miles. Still, I guess none of it matters anyway. The sensor seems to be working and that's the main thing. As for the service info, I think I'll just ignore it. :)
 
Thought the one on the ramp was just vehicle inspection. If I cycle through the service info I get a front half of the car icon and rear half of the car icon for the respective brakes on my E87
 
flybobbie said:
The brake pad wear sensor has two contact points. When the first is worn to, it starts measuring, when the second is worn it can work out how many miles left on pads at the wear rate its experiencing. (different pads/driving style different wear rates).
I think that's how it works having replaced pads and seen close up the wear sensor.
So all warnings are a bit of guess work as you may use the brakes less/more aggressively after the measurement period.

Say if the contact points are 1mm apart and it measures 20k miles for them both to register then it assumes a 5mm pad will be safe for another 60k. With 1mm left.
If that makes any sense.
Click to expand...

Are you sure about this? I have done brakes on E92 (3 series) and E81 (1 series) which both have condition based servicing. Both cars just had a normal pad wear sensor at front and back. By normal, I mean one which simply makes or breaks a contact and trips the "service due" when the pads get down to low.

I thought the condition based servicing simply uses information supplied by the DSC unit to monitor braking and then predict the pad mileage remaining for CBS?
 
My suggestion only a theory based on the position of the two wear contacts on the sensor.
Why have two contacts when one would suffice.
Unless one acts as a earth path.

Simple brass stud as worked for years on other cars.
 
flybobbie said:
My suggestion only a theory based on the position of the two wear contacts on the sensor.
Why have two contacts when one would suffice.
Unless one acts as a earth path.

Simple brass stud as worked for years on other cars.
Click to expand...

OK, for clarity, I am 99% that it does not work like this.

The pad wear sensor is simply a wire which when the pads get low, the circuit is broken, which puts a light on the dash.

I believe the CBS for brakes is done through the DSC module. The DSC module reports brake usage to the CBS system.

I think the CBS system then predicts the remaining life based on pedal presses, length of time on the pedal, pedal pressure, etc.
 
I don't know how it works.

I might suggest to BMW my theory, might make for a more accurate check of how long the pad will last!
 
flybobbie said:
I don't know how it works.

I might suggest to BMW my theory, might make for a more accurate check of how long the pad will last!
Click to expand...

Heh, try it. Doubt they will do it though because the extra wiring necessary would cost a quid or so per vehicle and the accountants will cost out.

To the Original Poster, every car I have had with this CBS system, the mileage countdown for the brake pads has been pretty much spot on. It will show 0 miles remaining usually just before the pad wear sensor will be destroyed and put the warning lights on the dash. I would suggest that at some point, someone has reset the CBS brake pad item on your vehicle without actually changing the pads, which has obviously then cocked up the countdown.
 
Thanks sniffer, that's just the info I needed :thumbsup: . I'll find out what's going on when I take the car in. Resetting the CBS seems the most likely cause but it would seem odd as the car only had 14k on the clock when I bought it.
 
Took her into my local indie this morning. Rear brake pads were the culprits and so the failure indicator did its job. I asked about the service indicator telling me I still have 15000 miles to go and the chap laughed. He said in his experience there are two types of CBS: those that work and predict wearing parts accurately and those that give out complete gibberish. I think mine must be in the gibberish category.
 
strugglinauthor said:
Took her into my local indie this morning. Rear brake pads were the culprits and so the failure indicator did its job. I asked about the service indicator telling me I still have 15000 miles to go and the chap laughed. He said in his experience there are two types of CBS: those that work and predict wearing parts accurately and those that give out complete gibberish. I think mine must be in the gibberish category.
Click to expand...

Heh, good you got it sorted. However, in my experience the CBS usually works pretty well and I think your indie is being somewhat of a cynic. :D

With CBS, the brakes will always be the ones you really are aware of because they are the item which literally wear down to nothing. If some fool has reset the oil or brake fluid, you may then run the fluid past its best and any negative effects/consequences, you would be unaware of. The air filters may look very dirty when you come to change them but you could put it down to the car running in a bad environment as opposed to them doing twice their designed service life. . . .

With the brake linings, factors which would muck it up could be someone changing the pads and using non OE pads which would have a totally different wear rate, or someone "correcting" the cars mileage and resetting the CBS items to not be caught out, or a mechanical fault down at the corner such as a lazy / sticky caliper.
 
Thanks sniffer, lots of useful info. :) Good thing is that the CBS will be reset after this pad change and so unless I sell her (unlikely) then I'll be able to see how things progress...
 
strugglinauthor said:
Thanks sniffer, lots of useful info. :) Good thing is that the CBS will be reset after this pad change and so unless I sell her (unlikely) then I'll be able to see how things progress...
Click to expand...

:D Yes, as long as the technician fits OE pads, be them supplied from BMW or a factors.
 
You must log in or register to reply here.
Back
Top Bottom