calibrating pad thickness

[mattylondon]

Hi Marcin, I do find it odd no errors were in the fault memory. If worn pads I would have expected the below. Maybe it is something with the Parking Brake module. And ceramics use the same rear caliper, although a different part number because it's painted gloss grey.

1 Fault Found:
02596 - Rear Brake Pads Worn 
            002 - Lower Limit Exceeded
             Freeze Frame:
                    Fault Status: 01100010
                    Fault Priority: 6
                    Fault Frequency: 16
                    Reset counter: 220
                    Mileage: 141904 km
                    Time Indication: 0
                    Date: 2016.04.19
                    Time: 11:55:44

[paulrstaylor]

Both motors had been replaced previously due to the usual corrosion/cracks/seizure issue, but I's still get occasional yellow or even red brake errors on the dash.

Put it down to an adaption issue, but couldn't get it right. re-adapted and even replaced the rear pads again - no dice.

Bought a second EPB "ECU" - but it wouldn't code to the 4.2 TDI as it was from an older model. Needed t sorted for the MOT so bit the bullet, local dealer had one in stock (says a lot I suspect), fitted, coded and issue resolved.

Never had an issue for the next year or so "Mechcanico Lee" will be able to confirm if he has had any issues since

[M-A8]

I know mate, very weird, Del is my witness. When I went to help him with the decoke we plugged the VCDS straight after coming back from shop without switching the engine off and found no faults at all in ABS.
But, I didn't look in EPB module, maybe that's were the clue is.
Will check it tomorrow if fault shows up on the dash and report back.

Cheers Paul. In all fairness I haven't tried re-adapting the module from pure laziness or lack of time in recent months and knowing that all pads are fine as they were just replaced. I am only getting the yellow warning light, no red.

[paulrstaylor]

That sounds familiar - from what I read at the time the control module contains a pair of MOSFETs which are designed to drive the motors - the theory was that when the motor seizes (or maybe the pads are not adapted properly) the motor pulls more current then the MOSFET can supply and so they get slowly cooked.

You can watch the current supplied through measuring blocks - I still have the old module on the shelf which I intended to open up but never got round to.

Again this is a distant memory, but think the cost of the new module was in the order of a couple of hundred pounds, so not cheap but was money well spent in my case

[paulrstaylor]

Oh and the codes will be in module 53 (EPB), not 03 (ABS)

I just checked, I don't have the logs on the PC from that time

[Mechcanico Lee]

It's been fine Paul

Got my head thinking this one , I do quite a bit of work on Bentley continentals , the rear calipers are very similar to the a8s but I'm sure the Bentleys have brake pad sensor wires on the pads .

So we saying a8s do not have sensor wires ?

So the plug that goes on the caliper who many wires are on it ?

[paulrstaylor]

Glad to hear that Lee

No pad wear sensors on the pads, my understanding is that the EPB module spins the motors until they draw pre-set current - implying clamping force had been achieved. Every now and then you hear them calibrate, they wind fully open an then closed, I guess that a simple time calc would give you the pad thickness - relying on the initial adaption to baseline?

[Mechcanico Lee]

Yes do hear it doing the calibrate thing , I see now that's how it works out the pad thickness , I was asking how many wires were at the plug because it could of had a tracking switch in the caliper and that's how it worked out pad thickness

[Rick]

The ceramics are smaller by 5mm on the fronts if i remember right. My s8 runs 385mm front discs and 335mm rears and the calipers are different to accomodate. Not sure on pad thickness though.
You can run steel discs with the ceramic setup but not the other way round.

[snapdragon]

There is a hall sensor that detects a spinning magnet passing by and so counts the number of turns. This is a source of many EPB problems due to the weak signal being implausible by the time it gets to EPB control unit and so was deleted on the later TRW EPBs as used in the D4 A8 etc...