Bimmerfest - BMW Forums - View Single Post - 2002 E39 ASC BRAKE ABS lights on => Diagnostic Procedure & Parts Location
View Single Post
Old 02-21-2011, 09:29 AM
jeffstri jeffstri is offline
Registered User
Location: CT
Join Date: Sep 2010
Posts: 45
Mein Auto: 740il
Originally Posted by bluebee View Post
You know that the fault code isn't a diagnostic solution; I know the fault code isn't a diagnostic solution; Bill knows this also ... but tell that to every Tom, Dick, and Harry that writes in that says "My mechanic says it's the brake pressure sensor".

How do I tell that person that what they are being told "is the problem" is merely the manifestation of the problem?

I do not know how to do that. It's easy to 'say' but it almost never sinks in.

Therefore, I don't know a "nice" way to get the point across. Do you? Bill has tried. Many times. Very many times. I generally tell them to read what Bill said.
When Tom, Dick or Harry says "My mechanic says it's the brake pressure sensor," I’d refer him to a post (if there is one – or make a new one) that clearly explains the difference between fault codes and a diagnosis. Then I would ask him to go back to the mechanic and ask what the fault code(s) was and what additional tests he (the mechanic) did to isolate the problem. If his mechanic was an indy, he likely just scanned for fault codes. Even if he was a BMW tech (at a dealer), he may have only scanned for fault codes – it’s more cost-effective (and profitable) for a dealer to throw parts at a problem as we all know too well..

Originally Posted by bluebee View Post
You understand what Bill said (even without reading it, as I can tell from your words); but you're not the scores of people who think all they need to do is replace this part or that sensor because it showed up in the "diagnostic test".

The simplest thing to tell them is that their mechanic doesn't have a clue what he's doing. It's not correct ... but how else do you actually get the point across to the myriad of people (and they keep coming) who think the "magical diagnostic scanners" will flawlessly pinpoint the specific bad part so they can just go out and replace it themselves?

I read all Bill’s posts in this thread before I made my first post, then re-read them before I made my last post, and just to be sure re-re-read them, and to simply say “read what Bill said” is very little help. If there’s a specific post of his which explains the difference between a fault code and making a diagnosis, why not refer Tom, Dick and Harry to it, or copy and paste the relevant part of Bill’s post, rather than make comments like “diagnostic machines can't tell you what you need to know because they're all hooked up wrong” or “their mechanic doesn't have a clue what he's doing”? I don’t think it’s the same Tom (or Dick or Harry) asking the same question here over and over again – Tom, Dick or Harry is almost always someone new, looking for information. Why not assume they can understand the difference between a fault code and making a diagnosis? You don’t have to re-create the explanation every time. If there’s already a good post, just refer to it or copy and paste.

Originally Posted by bluebee View Post
I don't profess to fully understand why, but, I have been here since March of 2008 and I don't recall a single person coming in who had a diagnostic done that truthfully pinpointed the problem when the (most common) problem REALLY was the one steel tack-welded wire on the Bosch 5.7 ABS control module lifting off it's gold bond pad or the extremely thin gold signal wires flopping against each other.

In that same time period, very many people have done diagnostic scans supposedly "pinpointing" various sensors, most commonly the brake pressure sensor and the steering wheel sensor in addition to the ubiquitous wheel speed sensors. Quite a few people have replaced 'em all (which is astounding to me), and in the end, they've had to have their ABS control module "rebuilt".

Bill has explained it far often than I can recall, in this thread, and in others (i.e., 540iman).
Probably because they just had fault codes scanned, just like you had initially, not a diagnosis.

Originally Posted by bluebee View Post
Basically, the diagnostic tools are great at describing symptoms but not at pinpointing the actual problem.
This is simply not correct. You (and Bill) continue to confuse (or maybe just obscure) the differences between fault code scanners (e.g., Carsoft 6.5) and “diagnostic tools” and between a fault code and a “diagnosis.” (By obscuring, I mean you often will say “diagnosis” when it appears you mean fault code.)

Bill apparently has only used Carsoft to read fault codes, except for one case where he did some work with a buddy who had INPA and Progman, but it’s not clear exactly what he did.

I don’t know how to make any clearer to you that BMW diagnostic tools such as DIS and INPA (and probably newer versions of Carsoft) do a lot more than read fault codes. The first thing you do with DIS is read fault codes. DIS then leads you through a series of additional tests to try to pinpoint the problem (i.e., make the diagnosis.) Some of the tests involve checking wires and connectors for continuity and shorts to ground, and resistance and voltage measurements, as you and Bill came up with for wheel speed sensors. Others are measurement of pressures and activation of components, which you do within DIS – no additional equipment is needed. Does DIS always pinpoint the problem? No – sometimes you do end up throwing parts at a problem, but less often than otherwise.

Originally Posted by bluebee View Post

The actual problem is most often either a bad wheel speed sensor (which is trivial to test with a DMM) or the ABS control module.
True, but pressure sensors, precharge pumps and other components do fail too.
Reply With Quote