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Hi,

I-Drive is requesting I replace the front brake pads in 1200 miles. It is a January 2005 build car.

A quick check of the calipers last night revealed that there is about 8-12mm of friction material left on all 4 pads. This is more that I would usually leave before replacing them. Any idea how thick new pads are?

What are others' experiences of pad wear? Is it usual to have a reminder to replace them when there is still quite a lot of material left?

I have run the car for about a year now, doing about 4000 miles - the countdown has moved from about 3000 miles to the 1200 that remains suggesting the wear sensor is wearing as it should.

Any thoughts or suggestions?

Thanks

Euan
 

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8-12mm - I've never seen 12mm on a new set!!

Usually about 8. If you haven't had it from new, maybe the previous owner changed the pads and didn't reset the indicator?
 

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Discussion Starter #3
This seems possible - pads changed but not the sensor.

Do you know whether changing only the sensor alone will give a higher mileage reading on I Drive as 'remaining' or whether I will have to plug in the diagnostics to readjust?

I would guess it will be immediately obvious if I put in a new sensor and it protrudes in front of the remaining pad material!

Euan
 

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Euan

I recently changed my front discs / pads / sensor. The iDrive was actually reporting about -700 miles until change! When I took the old pads off there was probably about 3-4mm of friction material left, so they certainly weren't "down to the bone", as it were.

I suppose it makes sense that the warning comes in early , can't see BMW risking a situation where an owner relies entirely on the car diagnostics, only to find that the pads wear out totally before any warnings appear and they subsequently crash, and blame the manufacturer! It sounds like afcneal is right, a previous owner has changed the pads and not changed the sensor or reset the iDrive. TBH the cost of the sensor is negligable, and it's simple enough to reset the system yourself, so no expensive trips to your local $tealer required...

As you said, changing the sensor and resetting the iDrive would resolve the issue, but I'm not sure what the situation would be if the sensor stands proud of the front face of the pad's surface material. As they're meant to wear together, I don't know if it would cause any braking issues, or maybe just damage the sensor? Mind you, it doesn't sound like your pads have been on the car long if they have that much "meat" left on them, so you mifght get away with it...

Jules
 

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This seems possible - pads changed but not the sensor.

Do you know whether changing only the sensor alone will give a higher mileage reading on I Drive as 'remaining' or whether I will have to plug in the diagnostics to readjust?

I would guess it will be immediately obvious if I put in a new sensor and it protrudes in front of the remaining pad material!

Euan
The reported distance on the I-drive is a facet of the reset, then a count-down based upon usage/mileage. The waer sensor only throws up the yellow wear warning light when it wears down itself (on the disc and completes a circuit). So you could reset the service indicator, but without knowing how worn the pads really are would need to ignore the count-down and react when the warning light comes on. As per bigjules the I-drive is very pessimistic and when I last changed mine there was maybe 1500 miles left!
 

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Discussion Starter #6
Spent a little time with the problem tonight and the plot thickens...

The 'new' wear sensor I got today is identical to the one already in the caliper and is not worn at all. There is even a slight clearance between the sensor and the disc as there is so much meat left on the pads.

As of yesterday, the red service light came on now showing brake service at -9000 miles and gives me a helful bong reminder every time i start the car.

Plugging in BMW GT1 diagnostics gives a DSC error code for the front brake sensor. Resetting the CBS service warning is not possible until this code is cleared and it will not clear as the fault is still present.

The wires from the wear sensor join the ABS sensor wires and then disappear into a large bundle that heads for the engine control module, then under the scuttle and round to the drivers side of the engine bay. Seems odd that the ABS is unaffected, must be those wires are still intact.

Between DIS and Bentley is seems possible (though unlikely) there is a broken wire between the wear sensor and the DSC unit. Have not explored this fully yet but it looks to be attached to the ABS unit under the bonnet. I hope it is this rather than a faulty DSC module!

Next step will be to disconnect the battery, remove DSC interface plug and check continuity between the relevant pins of the DSC plug and the wear sensor plug.

Lets hope this is something easily fixed!

Euan
 

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Hi Euaniebabs,

On this occasion I am not sure afcneil is right. I don't think the brake wear sensor is an 'off or on' sensor as per some older cars as he suggests, but actually is a wear sensor that changes its signal (i.e. resistance) as it wears down alongside the pads. In TIS it says that if you replace the sensor and the sensor is thicker than the remaining pad thickness you must file the sensor down to the appropriate thickness which seems to back this. I am a little surprised that you said the new wear sensor was thinner than the remaining brake pad thickness - certainly when I recently changed the rear pads (on my E60 535 car) the new sensor was the same thickness the new pads, as were they on my daughter's E91 front brakes when I replaced those. Was it actually a new sensor. Again TIS says that if you remove the sensor you must replace it with a new one as it loses its retention capability. Bottom line is I am not convinced your new sensor is working properly and thus throwing up the error codes you are seeing. I would double check that it is the right sensor (front not the thinner rear, or an already part worn one) and that it is inserted and connected properly. Good luck
 

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I'll certainly bow to the more knowledgeable on the electrickery of how the work!

What I do know if once the i-drive records 2k miles the sensor needs to be changed for the warning to be reset.
 

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Discussion Starter #9
Thank you all for your thoughts.

Managed to solve the problem at last but never did get a root cause.

While changing the brake fluid, I disconnected the battery for around 2 hours. I unplugged the DSC module (that was showing the errors) and checked the wiring back to both front a rear sensors from the pin out wiring diagram. Both circuits had little to no resistance across the sensors - around 0.05 OHM.

Blew out the connectors with compressed air, reassembled.

Connected DIS and reset front brake service. First attempt failed but second worked fine.

Reset error stored in DSC module and voila - problem solved!

IDrive now happy and showing ages before any more brake attention required.


Euan
 

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Just for info the sensor has two wires going to it. They simply loop through the sensor. When the pad wears it wears through this loop breaking the circuit. The only reason to file a new one is so it doesn't shatter the first time you apply the brakes. The sensor is a very brittle plastic and will break very easily indeed. I would never file a sensor though, if the disc is starting to contact it, one may as well change the pads as they will be showing a degree of wear if this is the case.
 
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