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Old 05-23-2009, 09:13 AM
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540iman 540iman is online now
resident, old fart
Location: N.W. Indiana
 
Join Date: Sep 2008
Posts: 1,505
Mein Auto: 2002 540i sport
You have done great work! And a lot of it, BTW!. You have a couple small let's say "inconsistencies". You do not need any alignment or other adjustment after doing a replacement unless you should find a "yaw" sensor as I call then is bad and this is seldom. If you need to replace a steering angle/yaw sensor, if you use diligent attention to get the new sensor angled at very close to the orientation of the old sensor, you are fine.

The biggest part to any DSC repair is diagnosis. Things can lead you in the wrong direction such as the three lights coming on and the speedo failing for instance. I believe more that one type of fault or bad sensor may cause the speedo to go out. We have a member I am working with now on this very problem. For me, my problem was the three light on and no speedo. It was my front right sensor. So, I believe the very, very first step should always be to test each sensor at the module connector. This way you also can see if the connection for the sensor is bad as well as the sensor itself. We are talking ABS senor/Wheel speed sensor here. The terms are used interchangeably. There is one on each wheel.. You must test each one at the module end of the cable to see what the module is seeing from each sensor. There are two ways to test, but I believe the diode test is more positive. A diode, almost by definition, conducts electricity only in one direction if it it working properly. A diode has polarity and only conducts one way. This is how they turn AC into DC. AC is always flowing current in both directions. DC flows only from positive to negative. It blocks that AC sine wave from flowing backwards so ac attached to a diode becomes 1/2 wave DC. It flows one way only. The wheel speed sensor has a diode action and to test it it should only conduct in one direction. Using a volt-ohm meter (VOM) with a diode check capability will show a good wheel sensor as "Open" in one direction" and a 1.75 volt drop in the other direction. By testing each sensor, you can take the guesswork out of it. If you use the resistance capability of the VOM to test a sensor, you should get around 3.3 Mega ohms in one direction and reversing the VOM test leads will yield approximately twice that first reading or say 7 mega ohms. You must be careful when doing it this way to not touch your fingers to the VOM probes or it is possible if your hands are sweaty to accidentally be measuring your body resisteance! That is why I chose the diode test method. If you find a sensor that is open or shows no voltage drop when checked in either direction, you have a bad sensor CIRCUIT. I say circuit and not sensor as we have not verified that we do not have a bad connection somewhere between the ABS module connector and the sensor itself. You have found potentially why you have the three lights, but the sensor could still be good and just have a badly corroded connection. You must check the sensor itself at the end of its pigtail to be sure. You can swap front sensors left to right or rear sensors left to right and if the nature of the error changes you have verified you have a sensor issue and not a module issue. Most sensors use the same 4mm Allen bolts to hold them in.

p.s. BlueBee, please send me your email address. Mine is wmliedtke@gmail.com I will send you the pictures I took. I could not get good closeups with the wife's good dital camera. It would not stay in focus. If you look at the underside of the connector, it is blue and has very tiny numbers at the sides. You can figure out what pin number is where. There are three rows of pins. You will need a small paper clip to get into the connector and not damage it.

Last edited by 540iman; 05-23-2009 at 09:20 AM.
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