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Old 09-12-2010, 05:00 PM
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540iman 540iman is offline
resident, old fart
Location: N.W. Indiana
 
Join Date: Sep 2008
Posts: 1,504
Mein Auto: 2002 540i sport
Quote:
Originally Posted by agent15 View Post
I understand what you're saying, but you've not clarified how the dealer's scanning tool, whatever make and model it is, said that the LR sensor was the one throwing the fault code. I would imagine there is a difference between a scanner pointing to a particular wheel's sensor as "open," as in a wiring issue or a failed sensor itself, versus the sensor telling the car's OBD system that it has an issue while still maintaining continuity to it.
I think you are saying that you understand, but are dismissing the thought process. The dealer's scan tool, Carsoft, or whatever scanners see many different symptoms that they don't like. Missing pulses, no pulses whatsoever, misshapen pulses as viewed on an oscilloscope, etc. They know what portion of the module they reside in. They can't tell the mechanic the cause, only the symptom. So, they identify the portion of the module that is whacked AT THAT MOMENT IN TIME. If the car were on a dyno and the wheels spinning, it would be better, but still not absolute because then it would possibly know if it is seeing pulses that the wiring is ok, but the sensor itself LIKELY bad. My Carsoft told me on my realtor's car that his sensor wiring was at fault when he actually had a bad sensor itself. I have no clue how it thought it could be so specific as to identify the wiring and not the sensor, but that is what it said. The same software, on my car, said it was the sensor itself-and it was after I confirmed by disconnecting and checking sensor with the VOM.

I am not discounting that the scanners can diagnose some faults (like communication faults) 100%. They can properly identify defective modules in many cases-say when a module is pulling no current whatsoever. Only the module can cause a symptom such as this. When it gets to the speed sensors themselves, they can be right still, but at a smaller percentage because of the nature of how the sensors generally fail. MOST (not all) go open. The cheaper scanners such as Carsoft assume the module itself works as long as it has communication. If a channel is dead, it will always diagnose as a bad sensor or sensor wiring. It will not return a bad I/O transistor in the module correctly. It will not diagnose a bad solder connection in the module as such. It will deliver a bad sensor message 100% unless the solder connection is not in the speed sensor signal path (again, like a communication error caused by a bad solder connection)-that it will get right. Talk to your Stealership tech. and they will tell you. Mark (aka EAC tuning Mark) has software very similar to what the stealer has and while he is working many of the bugs out of it, he will tell you that there is a big difference between accurately diagnosing the symptom and the actual cause. That can be trial and error. Many here will tell you of countless sensors diagnosed and replaced on to ultimately find it is the module itself.

I don't know if I clarified for you to your satisfaction. I can only tell you what is and why I as an electronic tech can justify it. Just do not believe that all bad sensor diagnosis are correct. People have spent countless dollars chasing supposedly bad sensors read by GT-1s down to Peakes.
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