Electronic Parking Brake - slave n/s motor from o/s motor?

Thread Starter

ladonamobile

Joined Aug 27, 2018
9
Hi, first post from a total newbie.
I had a seized parking brake motor on the left rear wheel of my VW Passat. (Now replaced)
I suspect it's failure also fried part of the Electronic Parking Brake ECU so that fault find software shows open circuit no power to left motor.
I opened the ECU up and replaced both large relays on the board but it has not fixed the problem.
My question is, can the nearside motor be driven from the working offside motor, effectively taking all it's instructions from the ECU right hand side?
Thanks in advance for any help, I can't really afford a new ECU and the ebay 2nd hand one I tried showed the same problem.
 

Thread Starter

ladonamobile

Joined Aug 27, 2018
9
I've checked the connector into the left motor but I can't check the continuity of the cable forward to the ECU because the brake ECU goes via the ABS ECU and I don't know which of the many pins feeds the parking brake motors. Both these modules are tucked away under the centre console where the handbrake lever would normally by positioned. I've spent many hours struggling with this and now want to investigate an out of the box workaround.
I'm thinking of connecting the working offside motors two wires into the nearside power supply connector.
Both motors are fed via 20amp fuses so think there is a danger of blowing the working side if I don't put relays in.
I need advice on the design of the circuit which covers the open/close aspect of the motors work.
 

Sensacell

Joined Jun 19, 2012
2,851
Unless you completely understand how the system works, your chances are not good.

The limit / control for one side is not going to control the other properly.
 

Thread Starter

ladonamobile

Joined Aug 27, 2018
9
I've limited understanding other than seeing the inside of the ECU which seems complicated!
I presume with the motors being low frequency short term use that if there is a lag on the limit /control, it won't put too much load on the faster finished motor. The offside motor only runs for a second or two in operation. I know it wouldn't be perfect, but as long as it doesn't blow the fuse at each use, I could live with it.
 

ArakelTheDragon

Joined Nov 18, 2016
1,353
The ECU logic is not complicated. Everything is CAN communication and that is it. It receives some message, than sends some message, either from CAN/Flexrat or another component and it uses this data to do its own things.

Example: if input by CAN speed too high -> output brake defence active.
 

shortbus

Joined Sep 30, 2009
8,701
Did you check continuity of the wires going to the one that isn't working? The best thing you can do when working on this kind of thing is to get a Chilton's or similar manual that has the wiring diagram. That will tell you what wire goes where, and in most cases the color of that wire. Some older cars have the wiring manual online too.
 

cork_ie

Joined Oct 8, 2011
428
You are referring to the Passat 3C, Parking brake holding power is dependent on clamping force on the rear disks , which in turn is dependent on a signal from the ESP longitudinal acceleration sensor providing information on the angle of the car on a slope. Clamping force is indirectly measured by monitoring the parking brake motors activation current seperately for each side. Don't even consider doing what you are considering, as you will either burst /overload the motor or else not apply sufficient clamping on a steep hill.
These cars have been around since at least 2006 and you should have no problem getting a secondhand unit in a breakers yard, at a reasonable price, cheaper than any alternative option.
Before you fit it make sure you take note of the coding number of the old unit also the coding on the ABS/ESP module as they will both revert to 00000 once you plug the new unit in. Then simply connect the new P Brake module and recode the ABS/ESP & P Brake modules using either a diagnostic tool or something like VCDS (Google it) you will then need to carry out settings and calibrations as detailed here:
http://wiki.ross-tech.com/wiki/index.php/VW_Passat_(3C)
 

Thread Starter

ladonamobile

Joined Aug 27, 2018
9
Thank you cork_ie, that is an authoritative answer and I much appreciate it.
I have already bought one second hand EPB ECU and found the n/s power supply was not corrected by installing it and doing a coding and re-coding. (Although that might be my inexperience, as it is a complicated process).
There may be a chance that the new/second hand ebay unit already had the same fault (it is common for n/s to fail o.c.) so I'm trying to get a known good ECU to test.
If that still doesn't sort it, what's the chance of building my own parking brake circuit from scratch like a parallel electric window operation from one up/down on/off rocker switch. Wouldn't the clamping force then be dependent on my input in the same way as a manual lever?
 

cork_ie

Joined Oct 8, 2011
428
Thank you cork_ie, that is an authoritative answer and I much appreciate it.
I have already bought one second hand EPB ECU and found the n/s power supply was not corrected by installing it and doing a coding and re-coding. (Although that might be my inexperience, as it is a complicated process).
There may be a chance that the new/second hand ebay unit already had the same fault (it is common for n/s to fail o.c.) so I'm trying to get a known good ECU to test.
If that still doesn't sort it, what's the chance of building my own parking brake circuit from scratch like a parallel electric window operation from one up/down on/off rocker switch. Wouldn't the clamping force then be dependent on my input in the same way as a manual lever?
First of all you would need to be able to write the software to communicate with the rest of the car etc. etc. otherwise you will have warning lights on the dash and this will be an issue on your MOT/ It would be far easier to win the national lottery.

It is very easy to test the motors and drive circuit. Lift the centre console sufficiently to get access to the connector plug and gently pull it sideways to get enough of the plug and cable out into the area between the seats, to test and make connections. There will be 8 heavy terminals and all the rest are tiny. The eight heavy pins are the lhs +&- and the lhs motor circuit , then the rhs +&- and rhs motor circuit. You can check which is which in seconds with your multimeter. Then with your ignition switched on connect two wires to the + & - of each side in turn and join briefly to the relevant motor terminals. That motor should turn, reverse the polarity and the motor should turn in the opposite direction. Voila!
 
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Thread Starter

ladonamobile

Joined Aug 27, 2018
9
Thank you again cork_ie.
My latest update is that this morning I bit the bullet and found a specialist independent VAG garage in the next town.
At the door at 08.30hrs and the owner plugged it in to his VAG diagnostics. He said he thought the new motors were out of sinc. and they needed manually moving, then the ecu's reprogrammed. I left it with him and had a nice mornings walk around the town.
I picked it up and it was all sorted, owner said all sincronised and fault codes cleared. Also new tight n/s motor connector fitted. I drove to my local MOT centre for 14.00hrs, they were busy but booked me an appointment for 16.00hrs. I went off to kill time by taking it to a hand car wash. On the way back the handbrake n/s failed again !! Went back home, cancelled MOT and put the car on VCDS.
Error on ABS module and EPB module.
Cleared ABS fault code ok, but EPB error flicks back up after each clearing:
1 Fault Found:
02432 - Supply Voltage for Left Parking Brake Motor (V282)
011 - Open Circuit - MIL ON
Next plan, duplicate what the VAG engineer did and race to MOT station before it fails again.
I'm still not happy with having my parking brake reliant on a flaky CANbus and liking the idea of rewiring the motor supply with 20amp wire and switch. Is there a way to blank the existing motor connectors to fool all ECU's that the motors are in place and doing nothing?
 

cork_ie

Joined Oct 8, 2011
428
Read what the fault code is saying !! You have a problem with the connection to the LH motor or the supply from the fuse for the LHS to the module. Is the fuse clean and bright?

This is nothing to do with the CANbus , which appears to be operating perfectly fine. If you had a CAN fault the right hand motor wouldn't operate either. You have most likely a faulty connection somewhere between the module and the LH motor, caused by movement of the suspension while driving the car. Double check you don't have a broken wire or damaged pin on the connector plugat the motor and double check that the rubber seal on the connector isn't swollen and causing the plug to back off slighly and cause poor mating.

http://wiki.ross-tech.com/wiki/index.php/02432
 

shortbus

Joined Sep 30, 2009
8,701
Yes you hit the nail on the head shortbus

Even in the age of computer driven everything in cars, it's still better to do the 'old school' things before looking into the controllers. Road damage or even rodents chewing on exposed wires, or connectors that vibrated loose or got corroded are still a problem. So when trouble shooting, that is where I start every time.
 

cork_ie

Joined Oct 8, 2011
428
Even in the age of computer driven everything in cars, it's still better to do the 'old school' things before looking into the controllers. Road damage or even rodents chewing on exposed wires, or connectors that vibrated loose or got corroded are still a problem. So when trouble shooting, that is where I start every time.
#Metoo
 

Thread Starter

ladonamobile

Joined Aug 27, 2018
9
Thanks guys, I've checked the fuses, but will give them a rub with emery. The reason I mention the CanBus is because the returned fault caused an error in the ABS unit too. It's all interconnected. With these intermittent problems it's like juggling plates. But not knowing which one caused the original domino effect. I've read somewhere that the EPB ecu will turn off the supply if the ABS is not set correctly. The ABS can trip if the EPB ECU loses it's code, etc. etc. So the error on supply could be hardwire and/or software. An intermittent hardwire fault is therefore a nightmare. That's why a solid copper end to end replacement is tempting me.
I don't think the fault is at the motor connector plug because VAG man put a new one on.
 

Thread Starter

ladonamobile

Joined Aug 27, 2018
9
Even this forum software is defeating me, the post above was supposed to be sent yesterday morning. I've just logged on and noticed it was 'greyed out' as if in draft format.
So yesterday (after the above) I set my stall out positioning the car to take wheels off and check connectors, resynchronise motors etc. but discovered that both brakes were working fine. Like all it needed was a few hours rest. Cleared error codes in VCDS, did autoscan and no errors came up.
I went ahead and cleaned fuses, checked motor connector and slack in feed wire around swingarm. No sign of anything, the wire is in a flexible concertina pipe and well protected.
Opened motors with service mode in VCDS and cleaned and copper greased the pads in the calipers.
On Monday it's book MOT and fingers crossed.
 

Thread Starter

ladonamobile

Joined Aug 27, 2018
9
Yes I do cork_ie. It's almost like the motor manufacturers are intentionally putting independents out of business.
Complex software controlled cars, with features nobody asked for (EPB's), inbuilt obsolescence, long warranties via main dealer, cheap finance on new sales.
Makes me want to buy an old classic car.
 
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