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Old 02-20-2011, 10:14 PM
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bluebee bluebee is offline
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Location: San Jose, California
Join Date: Mar 2008
Posts: 25,236
Mein Auto: 02 BMW 525i M54 auto 130K
Originally Posted by jeffstri View Post
There is a lot more that the BMW "diagnostics machines" can do than just read fault codes, which seems to be the only thing you and Bill have done with "diagnostic machines." The fault code itself is not mean to be a diagnosis.
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.

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?

BTW, at least the last poster actually fabricated the flying leads to further test the brake pressure sensor ... but how many people do that? (I didn't even bother ... and I'm really really big on diagnostics.)

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). Basically, the diagnostic tools are great at describing symptoms but not at pinpointing the actual problem.

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.
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