# How to replace/rebuild ABS ECU - ABS, ESP, Level Fault Workshop.



## cowboy_ (May 16, 2011)

My Symptoms: ABS light on, ESP light on, Level Fault Workshop and occasional no throttle issues. 

ABS and ESP will be off after the car has been sitting in the garage over night but after some drive the lights will go on. Other days will be on as soon as I started the car. 



ABS Light On 

ESP Light On 

 








(not my image, borrowed from post http://forums.vwvortex.com/showthread.php?5748624-Help!-Stranded-on-roadside&highlight=ABS+EPS) 



Level Fault Workshop Error. 

Transmission In Limp Mode and no Throttle. 

 









(not my image, borrowed from post http://forums.vwvortex.com/showthread.php?5748624-Help!-Stranded-on-roadside&highlight=ABS+EPS) 

For the first three problems I was not as concerned as I did not use the car that much but the fourth one, transmission in limp mode with NO throttle, was a big problem because it could start happening in the middle of a drive and you lose all power (no throttle) and people was not happy around me. 

I scanned the car and had different errors every time. Sometimes it was the Brake Pressure Sensor (G201) but the sensor will function properly when the car was not hot and sitting on my garage I could see the different values while pressing the brake pedal using VCDS. After driving the car for a while, the brake pressure will give me a reading of almost 220 bars consistently. 
On another scan I got a problem on all four wheel speed sensors, pretty much impossible to happen. 

I started researching the issue and found two posts related to this issue: 

Post 1 - It would be nice if the title and posts are changed from EPS to ESP as I was looking for ESP and couldn't find it. 

Post 2 - Again, the same problem, the function is called ESP but the post talks about EPS. 


After this I wanted to take my ABS ECU to be rebuilt or at least to be checked. I started this morning (Saturday 4/20/2013) disassembling the unit and it took me too long to be brave enough to do this. Never done anything like this before but it wasn't that bad after all. 

I took several pictures of the process and I hope this helps somebody else if they have this problem in the future. The ABS Hydraulic Unit is bolted to the ABS Pump itself. I've searched all over the place to see if removing the ECU was possible without disconnecting the hydraulic lines but not only I couldn't find any info about it but when I tried to do it myself was in vain. Removing the wheel liner doesn't give access to the motor bay. My only chance was to follow the manual. 
I read the manual several times and I tried to actually do it today. It took me only 2 ½ hours to remove the entire ABS Pump out of the car. It could be done in much less time if you have the proper instructions. 

The Bentley manual instructions are here. I will also post the images I took in the process. If there are any questions just post it here. 



Starting Point 

 










 Remove wheel - we need to remove a rubber plug to bleed the brake lines. 

 











 Rubber plug location. 

 











 This is the rubber plug we need to remove, you just have to remove it pulling it out.
 









With the plug removed. 











Open the hood 

 











Remove the right plastic cover – This is the location of the ABS hydraulic unit. 

 











We need to remove the intake tube 

 











Intake tube removed. Note the location of the ABS ECU. It is just the black portion of it, this is the ABS computer. 

 











Disconnect the brake pressure sensor connector (note the yellow repaired cables from the dealer doing me a favor to “try to fix the sensor before changing it”). 

 











Brake bleeder “kit”. I bought it from Advance Auto Parts. (us$8) 

 











The “fully” assembled kit (plug in the hose, done.) 

 











We need to connect the brake bleeder hose to the small pipe on the caliper, were we previously removed the rubber plug. 

 











This is how it looks 

 











Open the valve 

 











Some brake fluid will go down. At this point you should press the brake pedal for at least 60mm (according to the manual) and keep it in that position (I used a stick in between the seat and the pedal...taking care of the seat, of course.). If you release the brake pedal after pressing it air will be sucked into the brake lines and you don’t want that to happen (nothing really bad, just air that you need to later bleed out of the system). 

 











Picture to remember how everything was connected before start disassembling. 

 











Same as above 

 











Avoid spills of brake fluid around the ABS pump. 

 











And start removing the brake lines one by one. After I disconnected every line I put some plastic that when hot is very easy to give it shape but when it reaches room temperature it becomes hard like regular plastic. (this was not a good idea in the end, I’ll tell you more later). 

 











More lines removed. 

 











A very shaky picture from further away. 

 











We need to remove the ABS ECU connector. This is a regular VW connector, you have to slide out one of the sides to remove the connector. DO NOT pull the cable, you will not get it out that way. 

 











This is the piece of plastic that you need to slide out. It fits perfectly in your fingertips. 

 











Once slides out. 

 



















After you remove the connector is just a matter of wiggle the ABS pump a little bit and pull it out. This are 3 prongs that are just placed on top of 3 rubber rings. 

 



















The entire ABS Hydraulic Pump out of the car. This is a Bosch 5.7 ECU. 

 











There are 6 screws around the black case of the ABS pump. This is the ECU, we need to fix this computer. 

 











The ABS pump without the ECU. 

 











Various pictures of the ABS ECU/Pump: 

 



























Once you have the ECU out, that’s it. You can buy a new ECU (it is a KIT, around us$600), you can buy an entire ABS pump (around us$2000) or you can send it to rebuild. Personally I selected www.cheapabs.com because their turnaround time was great, many users were happy with their service and now I’m another one really happy with their service. They charged me $160 (including shipping) and they fixed the unit. 
As I’m kind of curious I wanted to know what was wrong with the computer as I also followed Willem’s instructions to fix the KESSY unit and I thought that the problem could be similar. So I opened the unit, again, you DON’T have to do this, I just did it to show you what's wrong with the computer. 

 



































And this is the problem. The silver wires on the top are bonded with ultrasonic techniques, but they expand and contract with the heat of the motor so at some point they just got loose and there is no connection with the computer anymore (they normally go out one at a time, I had 5 wires disconnected) 

 











You send it for repair, you wait until is back and you put it back in. 

 



















Once you connected all the brake lines connect the ECU connector. 

 











Connect the hose back. 

 











Everything connected back again 

 











Connect the batteries and this is what you get. At first I don’t have the ABS light anymore! One step closer! As always, every time you disconnect the batteries from the car you need to calibrate the steering wheel sensor (that’s why the yellow triangle is on (ESP)). And also the level fault is not there anymore! 

 











Ok, time for a small drive to fix the steering wheel sensor and is gone! 

 











Great! Steering wheel sensor calibrated. First time I don’t have the ABS, ESP and Level Fault errors on my display! 
As I didn’t want to have the TPMS error I switched the TPMS computer from one of my W12 to the other one (they have different versions, the one displaying an error is Firmware 21 and the other one is Firmware 26). So I swapped them and went for a ride. 

 











Finally not a single error on my display! Did a test drive for around 50 miles and everything is working as expected. 

Oh, before I forget, do you remember that I mentioned that it was not a good idea to use that plastic to cover the brake lines? A small piece of plastic went inside the brake lines and I ended up pumping the brake to get it out of the system! It took me like 15 minutes to get it out! So it is better if you use rubber plugs to cover the pipes or just a plastic bag to avoid brake fluid spills. 

 









I’m sorry for such a long post but I left a LOT of pictures out of the post to make it this “small”. 

Juan


----------



## Paximus (Aug 26, 2011)

Hi Juan, 

That is a really great contribution! Thanks for posting. 

Chris 


PS - the photos are not visible to someone not logged on to Google (most people) so if you are able to rehost it would be appreciated.


----------



## invisiblewave (Sep 22, 2008)

Juan, that's awesome (not a word I use lightly, despite my partial Americanization!). You'll probably be pleased to hear that it took my VW dealer 3 weeks and > $5000 to do the same thing. At the same time I had the problem, somebody else also did, and their dealer cost got to around $7000 because they incorrectly diagnosed a faulty transmission controller as well as a faulty ECU (which mine also did) before finally getting it right. 

Btw, I can't see the pictures despite being logged in to Google Docs. I can see the first two dash shots, but that's it.


----------



## IwasHuman (Jun 30, 2012)

I can't see the pics either. Was this a Bosch ABS controller? The reason I ask is because both my E39 540i and Volvo S70 had the same exact problem, needing repair of the solder connections that came loose from repeated heating and cooling. It was a very well known problem among those cars. It's interesting that it would cause the trans to go in to limp mode though. 

Glad you got it all sorted though, and nice write up! 

Aaron


----------



## invisiblewave (Sep 22, 2008)

Mine didn't affect the transmission, although I don't know why. The throttle was disabled, but I limped it home in idle and managed to get it as high as third gear on the way.


----------



## cowboy_ (May 16, 2011)

Thank you guys but this is just a small return on the investment everybody does on this forum. One of the main reasons I bought the Phaeton's is because of the knowledge that we have right here. 

Anyway, even when I work with computers (I do software for a living) I can't find a way to link a picture from google drive to anybody who wants to see it so I'm sharing the entire folder so I hope this works. 

https://drive.google.com/folderview?id=0B1WIJlfRMcsmTWdxXzdaVFhGLUU&usp=sharing 

Aaron: Yes, the controller we have in our Phaetons is the Bosch 5.7 (there are also 5.3 with the same problem). It is better to send it over for repair, the wires inside the controller are INCREDIBLY thin (and I'm used to build SMD electronics prototype boards) so it is not easy to fix by yourself. For the money it is much easier for somebody else to fix. There is a gel like product on top of the circuit and wires and you have to remove it before you can fix it but doing so you can break other wires (not sure if on the picture ZM.JPG you can see it but to the right side of the silver wires there are like 10 or 20 gold wires and those are even thinner than the silver ones, and removing this gel-like product breaks those gold wires so you have to be VERY careful if you try to fix it yourself. 

For our friends on the other side of the "pond" I will use the services of a company called ACTronics (they really rebuild this things from scratch as you can see on this video) 

This particular ABS ECU is fitted in several cars and in some of them the problems are pretty much the same as in ours (ABS, ESP, etc.). 

The transmission issue it will only happen if you get that particular wire disconnected from the ABS ECU, it all comes down to which wires you get disconnected inside the ABS ECU. The fun part of all this is that the ABS is pretty much off line after you have this problem and that's reflected on several other ECU's so it is difficult to pinpoint as the source of the problem. 

I'll try to move the pictures somewhere else and see if I can have them inline as that helps to see the process easier. 

Juan


----------



## invisiblewave (Sep 22, 2008)

This is extremely useful information even if you're not going to do the job yourself. Even if you paid an indy shop to to the job, you're still looking at saving nearly $2k on the part. 

I edited my posts in the other threads to change EPS to ESP, I think I just followed what someone had posted earlier.


----------



## cowboy_ (May 16, 2011)

Thank you, that will help future owners to find the thread easier.


----------



## WillemBal (Nov 20, 2010)

cowboy_ said:


> For our friends on the other side of the "pond" I will use the services of a company called ACTronics (they really rebuild this things from scratch as you can see on this video)


 Hi Juan, 

That is very useful information. I have seen all of their video's before as I was primarily interested in their capabilities to rebuild and create custom instrument clusters using colour displays. They also have good equipment to fully test controllers prior to shipment, so you are sure to receive controllers which do not have any hidden shortcomings. They can repair almost any type of damage, except for (water) damaged ECU's. They could be a good source for refurbished Kessy's although I've not yet seen them offering one. 

Willem


----------



## rangsudh (Mar 20, 2013)

Hi Juan,

Thanks a million for such a wonderfully clear and useful writeup!

I tackled the ABS ECU removal today and all went well, literally took less than an hour and I could probably do it in half an hour if I had to do it again -- I was a little reluctant to tug at various parts, so double-checked carefully before each step.

Very little brake fluid came out during the bleeding step, so I was a bit concerned that I had messed something up, but now I suspect I was just low on brake fluid to begin with.

VW sells a set of plastic threaded plugs that screw into the ABS pump from where the 6 brake lines were disconnected. These work very well to keep out dust from the pump while the ECU is out being repaired. And of course, there is no concern of using liquid plastic that might break off within the brake lines or pump. The part number for this is 1H0698311A -- it may have extra plugs because it may be used on multiple car models.

If you plan to tackle this, I also suggest reading the removal instructions on cheapabs.com and following the precautions outlined there.

Will post again once I have it all installed -- hope it will fix my warning lights. Apparently the Bosch 5.7 unit in our Phaetons can sometimes develop an irreparable memory fault that cannot be fixed without a new ECU.


----------



## DugSms (Apr 23, 2018)

IwasHuman said:


> I can't see the pics either. Was this a Bosch ABS controller? The reason I ask is because both my E39 540i and Volvo S70 had the same exact problem, needing repair of the solder connections that came loose from repeated heating and cooling. It was a very well known problem among those cars. It's interesting that it would cause the trans to go in to limp mode though.
> 
> Glad you got it all sorted though, and nice write up!
> 
> Aaron


I'm just now finding this thread, but I also had the same issue with my 2000 Volvo S70 ABS module. There is a guy in Minnesota that made a bit of a business just rebuilding these Volvo ABS units. I sent mine to him a few years ago and he had a "new" one back to me in about 2 days. I think that charge was closer to the $50 range. I found the link: https://www.midwest-abs.com/

I bet he would probably do the VW ones as well, since it looks like the exact same (type) of ABS controller as you mentioned. Although, fair warning, he would refuse to work on it if you opened it up before you sent it to him since he had a lot of people screw them up too badly and then they couldn't be refurbished.


----------



## rangsudh (Mar 20, 2013)

DugSms said:


> I'm just now finding this thread, but I also had the same issue with my 2000 Volvo S70 ABS module. There is a guy in Minnesota that made a bit of a business just rebuilding these Volvo ABS units. I sent mine to him a few years ago and he had a "new" one back to me in about 2 days. I think that charge was closer to the $50 range. I found the link: https://www.midwest-abs.com/
> 
> I bet he would probably do the VW ones as well, since it looks like the exact same (type) of ABS controller as you mentioned. Although, fair warning, he would refuse to work on it if you opened it up before you sent it to him since he had a lot of people screw them up too badly and then they couldn't be refurbished.


His website says they only service Volvo ABS and will not handle any other makes.


----------



## rangsudh (Mar 20, 2013)

Update (describing work carried out in 2018, over a year ago):

The original problem on my Phaeton was a DTC regarding "defective front-right wheel speed sensor."
The sensor was replaced by the dealership and no debris was found around the sensor. The problem went away for a while, then came back in a day or two.

I refused to believe there could be a problem with the brand new sensor and reluctant to take it back to the dealer. It appeared that after clearing the DTC on the wheel sensor, it would come back after some high-speed driving i.e. engine compartment heat.

This thread seemed to imply that such a heat-related error might be due to a bad ABS module (call this original module ABS_1), so I sent it off to cheapabs.com for a repair. It came back with the surprising comment that no fault was found. There was no charge but I did notice that the top of the ECU had been sliced open and when it was put back, the black sealant used was applied in a hurry and did not seem very robust.

Now I suspected that the ECU module passed a visual check of the internal wires and maybe even an electrical bench-test because the loose contact and related error was only triggered by heat. So the only way to eliminate the ECU as a suspect was to install another known-good ECU. Thus, I bought a used one from Ebay (call this ABS_2) and installed it as described in this thread.

Strangely enough, the wheel sensor fault did not disappear. Even if cleared, it would come back after a few hours of driving. I revisited my assumptions and decided to replace the brand-new wheel sensor the dealership had installed with a used part. Lo and behold, the fault cleared up and stayed cleared. I concluded that ABS_1 was actually trouble-free and set it aside as a spare since the ABS_2 installed on the car along with the replaced wheel speed sensor were working fine. [For whatever reason, the sensor that had been installed by the dealership was faulty. Or perhaps there was a loose contact. One in a million chance.]

Fast forward 9 months. We drove into the city for brunch. One hour freeway driving. The car performed flawlessly until we arrived and parked. After a couple hours, started the car up again and it would only start in limp mode, with PRNDS highlighted and road speed limited to 2.5 mph. Basically undriveable except out of the parking spot. At this point, the ABS woes had not occurred for a year, so there was no reason to suspect any ABS issue, it was easy to conclude that it was a new transmission-related issue. Had it towed back to the dealership.

[The car is smart enough not to enter limp mode on the highway, that would have been catastrophic. It smartly waited until we had reached the city and parked and only when restarting, limited itself to 2.5 mph. I double-checked this behavior later. But perhaps there is some set of faults where it will enter limp mode even in the midst of driving.]

Dealer tech investigated and found that the transmission was complaining of internal overheating, causing limp mode. Looked like the car had overheated on the long drive into the city. I change the transmission fluid every couple years, so it was surprising. Tech pulled the ATF fill bolt and found transmission was low on fluid by a bit (not a lot). They topped it off per factory procedures and road tested. Limp mode gone, no issues at all. So now we all concluded that the limp mode was definitely a transmission issue. A small leak over many months caused low fluid levels, causing high temperatures on the long drive to trigger limp mode. The leak was traced to pan bolts not being torqued properly at the last ATF replacement, and the bolts were tightened before fluid topoff. The fluid level was not low by much, and no external signs of leaking were visible, but the theory all seemed to fit.

At this point, I asked the dealership to keep the car for another day and drive it around a bit more to make sure there really were no remaining gremlins and the true root cause of the issue had been found. Sure enough, after extended driving, the sensor reported internal overheating again and car entered limp mode. Dealership said the only fix was to replace the entire transmission, but no new transmission available in the entire country. Not to mention, it would be thousands of dollars parts+labor. I decided to take the car back home and after resetting the faults using VAG-COM, drove it home with no issues.

At home, I was able to study the problem at leisure. After the car was left in one spot with engine running for 2 hours at idle, it would suddenly enter limp mode, even though car was stationary so transmission could not be getting super hot internally. This was completely repeatable. Around the same time, it would throw faults about "Supply voltage lower limit exceeded". I felt that perhaps the VPS battery was not charging as it should at idle and declining voltages caused a couple spurious errors, causing the transmission to report overheating and triggering limp mode.

After much tedious swapping around of the vehicle batteries with new ones, there was no improvement. That is when it hit me that perhaps it was an ABS ECU module issue. No problem, I thought, I have the spare ABS_1. I swapped the ABS_2 with the original fault-free ABS_1 to see if there was any improvement. The swap of course was non-trivial but not too bad. The limp mode after 2 hours went away, so there was clearly a problem with ABS_2 but now I was getting some different ABS errors from the ABS_1 module. Disconnected the ABS_1 ECU and drove like that for many days. Zero issues. After working for nearly a year, ABS_2 had given up the ghost due to repeated heat cycling and caused the limp mode on the transmission when a certain temperature was exceeded.

But why was ABS_1 reporting (very consistently) a different ABS fault when it was deemed trouble free? After all, it had been tested professionally when off the car and it was the wheel speed sensor that had the original problems. So I took out ABS_1 and closer inspection showed that due to poor job of inspection and resealing, two of the wires inside were touching/shorted together. Sigh. This had clearly happened after it was disassembled and bench-tested when the lid was put back together in a hurry. Honest mistake, I'm sure but aggravating none the less.

Hence I had to find yet another ABS module. Duly found one on Ebay, call it ABS_3. Was wary of another used unit, as who knew if it was flaky with heat due to internal wires detaching. But a rebuilt unit could only come from Germany and take many weeks. Installed ABS_3 and voila, all ABS faults disappeared and stayed that way. No limp mode or transmission issues either. Every time the ABS module is replaced, brakes must be bled and road tested with an ABS activation performed. This is where I faced a new issue. After the first such hard stop ABS kicked in and the car pulled to the right even when steering straight, the exact problem ABS is supposed to avoid. Sigh.

Back to debugging. No stored DTCs at all, just a minor pull to the right on normal braking and a more severe pull during ABS braking. Clearly, the brake bleeding was improperly done, there must be some air trapped in one of the lines. This was causing different force distribution at the wheels when braking, leading to the pull.

So bled and refilled the brakes multiple times, including bleeding the lines from the brake booster to the ABS modulator. Tried reverse-injection bleeding with special equipment. Tried vacuum bleeding, pressure bleeding and combinations of all the above in various wheel sequences. Tried various types of brake fluid. Pedal was now decidedly spongy, the pull was even more apparent, so clearly there was air trapped somewhere. Unlikely to be in the lines given all the bleeding, so perhaps it was air inside the ABS_3 modulator hydraulic unit itself.

There are stern warnings in the factory repair information to never let the brake fluid inside the ABS hydraulic unit drain, as it would otherwise be impossible to bleed using conventional bleeding equipment. I learnt that such units would require a factory bleed or a shop bleed using a scan tool to pulse the ABS internal valves during bleeding. VAG-COM does not support such electronic bleeding procedures but I found a scan tool that does so for these Bosch 5.7 units. After renting that tool and successfully using it to bleed the ABS module, tried road testing again. No use.

At this point, I realized that perhaps the ABS_3 module's electronic control unit (the black plastic ECU half) and its internals were fine, but perhaps the hydraulic control unit (the metallic half) was not. It had air trapped in it that could not be bled given the narrow internal passageways with any equipment other than Bosch's own factory equipment, perhaps not even VW equipment. That is why new ABS modules are shipped pre-bled with fluid inside and sealing caps that must not be taken off until just before installation.

So now I took the hydraulic part of ABS_1 and mated it to the electronic part of ABS_3. Installed this combination and bled the brakes all over again. No electronic codes. Road test flawless. This confirmed that the hydraulic portion of ABS_3 had a physical fault and could not be bled even though the scan tool bleed had succeeded.

Closely inspected ABS_3 hydraulic unit on the bench. Found that one particular port combination was allowing fluid only one way but not in reverse, likely due to an internal check valve that was stuck due to missing fluid and resulting internal corrosion. Thus, normal braking was fine, except for a minor pull, but ABS braking was decidedly pulling. Then I recalled that only ABS_3 had arrived without the plastic sealing plugs described in this thread to keep the fluid from leaking or evaporating. So even though I had successfully bled all the air out of the ABS module internals, it was not able to stay that way due to the internal stuck valve. The more I road-tested it with hard ABS braking, the more it would "unbleed" itself.

Moral of the story: If you buy used ABS modules from Ebay, ensure that the ports have been plugged as soon as taken off the donor car. Never buy a unit that does not have the plugs. Some used units will have the brake lines still attached and crimped off so that the brake fluid cannot leak out. These might be fine. Also the ABS unit should not be tilted when the holes are unplugged, as it could leak out some fluid and develop an internal air pocket. As the factory manual says, do not remove the plugs until it is in place and in the correct orientation. Also, do plug your unit using the factory plug kit before you take the ABS module out of its resting place in your car or even tilt it.

Now, you could do as I did and retain the hydraulic part of your ABS module while replacing the electronic part, since the latter is usually what fails with heat. If you do so, then it doesn't matter if the ABS module you buy used has the plugs or the brake lines crimped off, as you will only be replacing the electrical ECU part. The factory manual advises against this, though I can't see a great reason for it. There is no specific matching, calibration or adaptation between the two. The issue is probably that some fine dust or dirt or even some moisture can get in between the two and cause corrosion or rust on the pintles of the solenoids, which are polished steel. But if you are going to remove the electronic part for rebuild purposes, then you have already exposed the solenoids to external agents.

Note that the big 42-pin ABS wiring connector from the vehicle harness to the ABS module has a bit of a trick to unlatch/disconnect. It has a black plastic lever on top that locks the connector into the ABS unit electrical socket. This lever must be swung through a 135-degree arc to release the connector before pulling the wiring connector off the unit. Pulling the black piece visible in the earlier photo on this thread may work as it is connected to the lever, but it is the lever that is the primary part that must be moved to lock/unlock the connector.

Not knowing this, I destroyed the lever and connector at one point and then had to get a replacement connector and transfer all 42 wires from the old to the new one.

Anyhoo, all's well that ends well. No ABS or transmission issues any more. Even under severe testing.


----------



## Paximus (Aug 26, 2011)

> *Moral of the story: If you buy used ABS modules from Ebay, ensure that the ports have been plugged as soon as taken off the donor car. Never buy a unit that does not have the plugs. Also the ABS unit should not be tilted when the holes are unplugged, as it could leak out some fluid and develop an internal air pocket. As the factory manual says, do not remove the plugs until it is in place and in the correct orientation. Also, do plug your unit using the factory plug kit before you take the ABS module out of its resting place in your car or even tilt it.*


Hi rangsudh,

Thanks for that thorough and excellent description of your persistent approach.

It's an example of the interwoven faults that can occur, leading dealers (and owners) up an expensive garden path.

Great contribution. :thumbup:

Chris


----------



## richmondvatdi (May 17, 2003)

*This thread gives me hope*

I logged on tonight intending to start a new thread titled: "Is there any way to tell from a VCDS scan what is causing limp mode?" Instead, I stumbled onto this thread and after reading all the posts I am convinced that the ABS Control module could very likely be causing my mysterious limp mode. The limp mode is so unpredictable that I have not been able to take the car onto the road, because when it happens, the car won't go above about 900 RPM. Last time it happened 90 miles from home and the AAA tow was a nightmare (another long story). Anyway, this weekend, the ABS control module is coming out and getting shipped out for repair.

Quick question: where can I get the kit to plug the connections once I remove the brake lines? (Having gotten air into my B5.5 Passat ABS unit and gone through the trauma of having to remove it, I am now overly careful). As an alternate, can I just use an equivalent metric bolt and if so, what is the thread size of those holes?


----------



## invisiblewave (Sep 22, 2008)

You can test if it's the ABS controller simply by pulling out the plug. As soon as you do, the throttle will start working again. The reason it goes intermittent, getting steadily worse, is because it's heat-soak-related.


----------



## rangsudh (Mar 20, 2013)

Yes, drive it around with the ABS electrical connector unplugged and see if the limp mode problems go away. You will not have ABS braking but will have regular braking in that period. Nevertheless, be careful.

We also need to be careful about forcing the electrical connector out. In the photo attached, you can see how the connector looks when its latching Lever has almost finished unlatching. The latching Lever is the black plastic part with a couple of cogs visible on it, resting around 45 degrees to horizontal, with "Made in Germany" stamped on it. When installed on the car, this Lever will rest at 135 degrees to horizontal. This needs to be swung towards the firewall of the car (clockwise wrt the photo) so that it rests at 0 degrees to horizontal. As this Lever rotates through its travel of 135 degrees from fully latched to fully unlatched, the cogs at its fulcrum (pivot point) will pull in (to the right in the photo) the black rectangular Piece at the bottom left (it has two circular cutouts where you can place a finger each to push or pull as needed).

Also, you should slide in or out this rectangular Piece only when simultaneously pivoting the attached lever. The latching Lever is the primary mechanism, the rectangular Piece is secondary. As you can see in the photo, the Lever has a small slit in it that snaps into one of two detents when it is either fully latched or fully unlatched.

The VAG part number for the plastic plug kits is mentioned in post #10 above. It should be available from any VW dealer or parts store.


----------



## richmondvatdi (May 17, 2003)

*Uh oh.*

I carefully removed the ABS module. I opened the bleeder screw on the LF caliper, pushed the brake pedal in the required amount, retightened (closed) the screw. On the ABS module itself I removed one brake line at a time and immediately plugged the hole with the correct VW plastic plugs (both white and black depending on the thread size). Sent it off to cheapabs.com and it came back repaired today. I used the same care in reinstalling it. I removed each plug just before connecting the corresponding line. Hooked everything back up and started the car. Pushed on the brake pedal and it goes straight to the floor with almost no resistance. There is no brake fluid leaking anywhere and all connections are tight, including the bleeder screw on the LF brake caliper. I did an autoscan and am clearing codes now (since the battery has been disconnected for almost 2 weeks).

What besides air in the lines can be causing this? I just hope and pray that if there is air in the system, it's not in the ABS module because I'm not sure what to do at that point. Any ideas?

Paul


----------



## rangsudh (Mar 20, 2013)

In spite of all precautions, the car will need to be bled once after the ABS module is reinstalled. You didn't mention if you did that.

Some air would have entered the brake lines that were disconnected from the module, both the lines from the brake master cylinder to the module, and from the module to the wheel cylinders.

The factory procedure is:

Reinstall ABS module and hook up all 6 brake lines.
Release the brake pedal depressor inside the car (this should have been installed when the ABS module was removed and left there. Else if you were driving the car in the interim without the ABS electronic ECU, the pedal depressor should have been reinstalled before the ABS module was put back.)

Wait a little, for any air in the 2 inlet lines to bubble back up to the master cylinder.
Assuming you had plugged the ABS hydraulic module ports properly, air from the 4 outlet lines will not rise naturally into the hydraulic unit, because of check valves and narrow internal pathways. Note also that it is okay for air to get into the ABS module in certain circumstances -- i.e. the normal flow path of fluid from master to wheel through the ABS unit when no ABS valves are activated. Such trapped air will be able to be bled out normally.

Now, bleed all 4 wheels using the factory procedure and recommended sequence.
The Schwaben or Motive pressure bleeding tools work well but they do not go to as high a pressure as the VAG factory tool recommends, so having a helper pump the brakes works even better.
If you run into severe bleedability problems, you can try a Phoenix reverse injector bleeding tool. But this should be a last resort as it can force air into the wrong parts of the ABS unit if you are not careful.

Do not trigger an ABS activation during road testing unless you have first solved the soft pedal issue, you could introduce air into the ABS unit by doing so.


----------



## rangsudh (Mar 20, 2013)

Also, never ever push the brake pedal all the way down to the floor, even while attempting to bleed. Stop at the normal point where it would have stopped. You can damage the seals in the master cylinder if this precaution is not followed. You can place a block of wood under the brake pedal to limit the pedal travel.

You only sent the electronic part to cheapabs, correct?


----------



## richmondvatdi (May 17, 2003)

rangsudh said:


> Also, never ever push the brake pedal all the way down to the floor, even while attempting to bleed. Stop at the normal point where it would have stopped. You can damage the seals in the master cylinder if this precaution is not followed. You can place a block of wood under the brake pedal to limit the pedal travel.
> 
> You only sent the electronic part to cheapabs, correct?


Well, I pushed the pedal down pretty far but not all the way to the floor, but based on what you say above I may be replacing (or rebuilding) the master cylinder as well.

Yes. I only sent the electronic part out for repair. The work order had the box checked next to "defective and we SUCCESSFULLY repaired it" so I am hopeful that the defective control module was causing the limp mode issue that made the car undrivable for the past year. Fingers crossed.

When I put it back together I was expecting some sponginess because I assumed at least a tiny bit of air entered the system during this process. I just wasn't expecting it to be as soft as it is. I will do the full old-fashioned two-man bleed. (Sometimes the Motiv power bleeder method works, but sometimes it doesn't. I learned this lesson when bleeding my B5.5 Passat after the ABS module was taken out and reinstalled. Multiple bleeds with the Motiv could not get rid of the spongy pedal, but one complete two-man pedal-pushing bleed did the trick.)

We're leaving for vacation tomorrow morning, and there will be a ton of preparation to do tonight, but I would love to get these brakes bled. It would be great to leave for vacation knowing that there's a good chance I'll be driving the Phaeton again when I get back. 

Paul


----------



## rangsudh (Mar 20, 2013)

I know exactly what you mean, Paul. Here's hoping it all comes together soon on your Phaeton.

You left the brake pedal depressor installed all the time while the ECU was out, or did you use the hydraulic unit standalone and drive the car in the interim?


----------



## richmondvatdi (May 17, 2003)

I wedged an ice scraper between the driver seat and the brake pedal to keep it depressed while the control unit was being repaired.


----------



## richmondvatdi (May 17, 2003)

*Update:*

I got home this week and did a full 2-man brake bleed. Not surprisingly there was a lot of air in the system and the fluid was fairly dirty/cloudy. I used an entire quart for the process. I probably could have used less but I wanted to be absolutely sure I got all the air out. Started the car, ran an autoscan, cleared the codes and went for a drive for the first time in well over a year. The car runs great. No more "Fault Level Workshop" or any fault codes. I've taken it on 5 or 6 short trips this weekend (<10 miles each). As I get more confident I'll start venturing further from home.

It's amazing that ABS controller issues can impact so many different systems. This thread was a huge help in getting the Phaeton running again. Thanks to all who contributed.
Paul

P.S. Now on to search the forums to solve the "no a/c" issue...


----------

