ABS Bosch 5.3 Module

Discussion in 'General Technical Questions and Answers' started by N3IDT, Aug 4, 2008.

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  1. N3IDT

    N3IDT Ham Member QRZ Page

    Have started an attempt to repair a Passat ABS module. As per a Russian website, I found the common problem of two aluminum wirebonds broken that supply power to the board. My stereo microscope is seeing double so I used it mono and accidentally broke a gold wirebond next door. I almost had it made when I soldered a 30 ga jumper in but in trying to reposition the wire, the wirebond pad came off the board. Don't ask why I'm trying this; I'm trying to save 600 bucks or more. My last wirebond experience was as an engineer for the Pulsar watch back in 1976; I guess I'm a little rusty. Has anyone out there tried repairs to boards using silver conductive epoxy? There is a tiny spot left wheere the VIA is. I just ordered some epoxy from Mouser and I'm interested in any tips.

    Just to make working on this board more miserable, Bosch has a heavy gooey gel covering the chips and bonds. Nasty to remove without messing up.
  2. AJ4KS

    AJ4KS Ham Member QRZ Page

    Indeed the unit is expensive but unfortunately I have never seen anyone make a lasting repair to such a unit. Because of the cost, you are not the first to try.

    Don't repair it. This is a safety critical item. Once the back is open the device is not to be relied on again. This is a very delicate device and must withstand severe environmental extremes. Malfunctions are not limited to ABS specific failures but can affect the entire brake system. Indeed it is designed to "fail safe" but nothing is guaranteed now that the device has been tampered with. If one valve is in the wrong position you will lose ALL brake functionality and if you see the hydraulic schematic for this device these modes of failure are very clear.

    The block is a disposable item anyway. It will fail itself after a certain number of valve actuations even if it's working fine. I have seen a lot of these where individual valves start to leak too, but all these have been over 10 years old.

    Probably best is to replace the unit with a new one or a used one that has not been tampered with.

    If this block does not have a separate ABS control unit (ie. fully integrated) then any replacement - new or from a used auto - will have to be programmed for the car chassis. You may find that you will not be able to clear the faults in the ABS unit after it's reassembled. The dealer's computer may be required, this is not casual enough for aftermarket tools like vag-com.

    Another manufacturer is helping owners with these. Reports range from no help at all given, to the corp pays for the new part and customer pays for stealer shop and computer time. And some of these cars are 1994 builds that have been out of warranty for 8+ years. :)
  3. N3IDT

    N3IDT Ham Member QRZ Page


    I appreciate the advice of what I can tell is an expert mechanic/technician. He is totally right. However, challenged by my 55 years of soldering experience, I soldered the B+ lead that was broken and silver epoxied the 2 broken data wirebonds on the board. So far we have success. I only take exception in the advice given that if you complete a previously compromised circuit connection, it should not change the original logic. I hope that VW has built redundancy in their system. I cannot imagine that a single solenoid valve malfunction could cause complete brake failure, but I have not studied the hydraulic circuit to know. If this is true, please give me the name of a good class action attorney cause millions of us are going to need one. So far, I will say that the Passat has been a $$$$$$ (money pit). If you are thinking about buying one please see me about ocean front property in Arizona. PS The wifoid bought it, not me!!
  4. AJ4KS

    AJ4KS Ham Member QRZ Page

    Your skills are definitely not what I'm concerned about! What I want you to consider are the safety implications of such an experiment on a road going car, and that replacement of the device may not cost as much as you are expecting. I support your DIY repair spirit, and probably years of taking care of all your family's cars. But another failure in this component means the car is out of service for more days unexpectedly, which may or may not be worth $300 or $600 to you, or maybe something more serious worth avoiding like a call to the insurance company or paramedics.

    A professional should never recommend any ad hoc repairs to safety systems. Ever! In a car these are the brake/traction and airbag.

    There is nothing negligent from a safety standpoint in the design of your car. Yours is not much different from the version that was sold in Germany which got a TuV type certification.

    About valves in this thing: Mechanical valve failure is supposed to be prevented by the "actuation counter" logic bomb built-in. It refuses to work when the guaranteed time is over.

    One operational fundamental is the unit must be able to bleed off pressure, this is accomplished with a valve in each circuit that opens a path back to the fluid reservoir. You probably saw where the solenoids push the valves, and how many there are. If the wrong one of these would get stuck open, you still have one brake pedal (or one electric pump) making pressure for three or four brake circuits, so it will affect the performance of the others. This is one unlikely but plausible situation and as you can see it would be similar to a brake line rusting through or getting sliced open.

    This whole thing was assembled, tested and sealed by robot in a clean room. My hands aren't so precise and I'm ignorant of the original manufacturing process so I don't have confidence that I can make a repair of the same quality (even tho it failed in your unit it still passed the tests and met whatever engineering requirements) or know how long it will last.

    Once the block is unsealed is there a danger of dust or something messing up the action of the valves... or if something got scratched? What if an accidental short inside the device causes an inappropriate action? Maybe even if the repair fails soon then ABS deactivation is a safety issue by itself, since most of us are used to ABS by now and forgot how to modulate the brake pedal.

    It is unfortunate that the situation beckons replacement of the part but the high level of integration and complex manufacturing process is a cost compromise that enabled this technology to be included in your car. It is amazing for the time it was designed. Bosch do not want to keep supplying these units, they want to use their plants to fill current contracts that make all their money. VW do not want to distribute them. They really expected them to last as long as the car.

    You can probably save a few hundred dollars in the replacement cost since Bosch is aftermarket-friendly, or, because you can find a real VW dealer online who sells parts online at wholesale prices. Research these things:
    - Bosch number engraved on part
    - VW part number
    - Is any coding / initialization required when this part is replaced and can this be accomplished only at the dealer or can it be done with an enthusiast tool like VAGcom
    - What is the bleeding routine for the ABS system and can it be done with an enthusiast tool

    Even if you have to bring the car into the dealer for coding and bleeding, this will cost much less than if they do the complete replacement job. You can bleed it 'good enough to drive to the shop' yourself but I always hook up the computer and do whatever the factory manual/TIS says before the vehicle goes back in service.

    I have certainly heard some things about common VW concerns or failures that should not exist. These must only add to common frustrations that come with getting to know German designed cars. If you buy another one, try to get the final year of production of the model you want.
  5. WA6MHZ

    WA6MHZ Premium Subscriber QRZ Page

    ABS went out on my 96 Lincoln Town car after I had a non-dealership place do the brakes. Of course, the place denied harming the ABS and the Dealer said I was welcome to pay $700 for a new ABS module. Not having anywhere near that kind of money (especially after just paying out $400 for the brake job) I just said "Guess I won't have ABS" and that was that. The car has run for many years since without the annoying pulse pulse pulse when I slam on the brakes. It works just like all the old cars did before ABS. So, while ABS might be a supposedly superior system and a technology leap, alot of drivers got along without it for nearly a century, and so can I. I don't even want to think what one for my 2005 Town Car would cost!
  6. N3IDT

    N3IDT Ham Member QRZ Page

    There does seem to be something inherently wrong with these units. Only the Heavy double buss aluminum wires break on the board. Rebuild sites BS people for $200 to repair. I can see the fault is that the resonant frequency of the connection falls within the range of the vehicle's vibrations and the wire self destructs. I have now 4 days on the repair and all is well. I have not opened the hydraulic circuit at all so that has not been compromised. The unit self tests ok. When I replace pads on abs cars, I always bleed so as not to push contaminated fluid back towards the abs pump. Here in Florida we do not get a lot of abs action. I know that the abs units have a finite number of cycles of operation before failure; I hope we are not approaching that. I am not an ASE mechanic, but I know many as friends and always ask for advice. If the unit does fail, I have the stamped number off the block and have matched it to a replacement for $496, if that becomes necessary. As I said before, the repair was done using an eye surgery microscope. I have no idea how the Russians did it without such equipment.
  7. AJ4KS

    AJ4KS Ham Member QRZ Page

    The self destruct counter should be nowhere near expiry. My car's is still below 50%, it is a 97 build with over 150,000 miles.

    All the fluid will get contaminated over time regardless. Normal braking mixes it up, clutch action too if you have one. If you have concerns about contamination then flushing the brake fluid out will put an end to that. There is only 3-4cc or so trapped in the ABS block so you can get a satisfactory result without any tricks.
  8. K8MHZ

    K8MHZ Ham Member QRZ Page

    I can tell that HRPP is up to snuff on ABS.

    I was trained in the early 90s on the Teves systems. I got to try them when the first hit the market and I liked them over the Bosch system.

    After being 'in the business' for a couple years the thought of DIY and ABS mixing is a scary one.
  9. N3IDT

    N3IDT Ham Member QRZ Page

    Shade tree mechanics can be scary. I took a part time job in the 70's as the night mechanic at a Sunoco station. Learned brake and tuneup stuff. This ABS is still going. I did not open the hydraulic circuit or mess with the valve block. I only repaired a broken connection on the electronics board. I was careful about ESD. Now if I could just figure out where the 3 gallons of water came from that filled the back seat floor from TS FAY that just blew thru. Bottom line: This German engineered car has been the most expensive to maintain in my 45 years of driving. Oh, yes, the XYL chose it against my instinct, BUT it's CUTE! Tried to park it in the flood zone, but Fay left before the water got high enough. Note to insurance agents: that was a joke!
  10. AUDI20V

    AUDI20V QRZ Member

    Hey, I'm also in the process of repairing a 5.3 module.

    First, how do you get those aluminum wires to take solder? No matter what I tried, I couldn't solder to them.

    Second, how do you replace a pad once it is lifted up? I broke a bunch of those gold wirebonds in the process and replaced them with 30ga wire, but I accidently lifted up a few pads. I tried soldering directly to the vias using some flux, which kind of seemed to work, but I don't know. Is there any way to attach a new pad? I have some copper tape, but I can't make it stick and there is no way to attach the new pad to the via. Is there such a thing as conductive epoxy?

    Third, I was going to replace the 2 main aluminum busbars with copper wires, but I lifted up the main pad on the board side! This pad has 6 vias under it and there is no way for me to solder directly to all those vias. Is there any way I can put a new pad down here or am I pretty much screwed?
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