Early E39 Wheel speed Sensor Diagnostics

[DennisG01]

(Click pics to make them bigger)

I have an early production 528. I mention that since a lot of the information found throughout the forum/online often applies to (my guess) '99+ E39's. For example, my car has ASC traction control, not DSC traction control. Also, the ABS module (computer) is behind my glovebox, not in the engine bay. I have been having intermittent issues with the Triangle/Traction Control light and ABS light coming on. When this happens, the transmission goes into some type of "safe" mode where it seems to only allow 2nd and 3rd gear (4-speed AT). I can manually shift through the gear, however, to get 1st and 4th gear. During the time when the lights are on, I have no other problems (speedo/tach/odometer/cruise control continue to work). Although, I wonder if that is due, at least in part, to which particular WSS is failing? Lately, it has been less intermittent and more permanent...

When I scan for codes (after earlier clearing them) I get:


I looked through a lot of threads and the DIY section and eventually was able to find Post #346 by BlueBee here: https://www.bimmerfest.com/forums/sh...52#post5882252

Although the picture of the connector (yellow plastic innards) seems to be optically reversed, you can figure out the appropriate pins by simply comparing/counting holes from one side or the other. So... followed the procedure outlined in that thread, using my DMM set to diode mode. I tested all four WSS and the the front/left was, indeed, different than the other three. NOTE: My voltages, below, are different than what is noted in that thread - which I assume is because the voltages listed in that thread are for a newer system. Below are my results, with the second number being when I tested in "reverse" (reversing the DMM leads).

F/L: .559V .517V
F/R: .705V .583V
R/L: .705V .579V
R/R: .698V .580V

I then removed the Front/Left WSS and tested it directly at it's connector and got the same results (within a few mV, anyways).

Based on this, I ordered a Siemens/VDO WSS from FCP. I should have it in a couple days and will post back - hopefully with positive results!

Just as a side note, my "tone wheel" or "reluctor" (not sure which is the correct term... or both?) is not the typical "toothed design". Instead, it has a wavy groove routed out from it, thereby creating the "gap" needed. The darker "stripe" in this picture is the routed-out groove. The gold area is the solid, un-routed, disc that rotates when the wheel turns. I did take a video, but not sure how to post that as "PostImages" doesn't take videos.

[makenzie71]

I had those same codes (plus some others related to ABS system) and the solution was just that...new sensors. I still get the intermittent interference one and can't pin it down to anything.

[DennisG01]

I had those same codes (plus some others related to ABS system) and the solution was just that...new sensors. I still get the intermittent interference one and can't pin it down to anything.

I'm curious about that intermittent one, as well. We'll see if it pops back up for me. I wonder if it's something like dirt getting into the reluctor wheel for a short period of time? Meaning, a short time where the computer sees an error reading won't activate the warning lights? I'm only guessing at that, though.

[DennisG01]

Follow up... I installed the new sensor today. It tested with the same voltage as the other three, by the way. Cleared the code, the ABS and Triangle light went out. Drove for about 20 minutes and they did not light up again. Hard to believe that about a 1/10 of a volt is all it takes for one to be bad.

[mattmar1]

in testing the WSS units as you are, youre looking at resistance, not voltage readings. fwd/reverse biasing of diodes.
ive rarely seen an e39 ABS system that doesnt get the intermittent interference fault while the system operates without error.

[DennisG01]

I'll admit that I don't quite understand how I could be measuring AC voltage with no source of power in the circuit. But according the thread I referenced above, that is exactly what I was doing. Unless the power comes from my DMM (set to the "capacitance" setting)? There was ALSO mention of a resistance test that can be done (with DMM on Ohms), but I didn't do that.

[mattmar1]

i havent looked at the thread you mentioned yet, will when i get a chance (bluebee's threads, god bless her, on the fest are very comprehensive compilations of info, and her organizing of them is exceptional). that you have a DMM capable of determining capacitance says that you have one that is above average. youre correct with your statement of not understanding how you could be measuring AC voltage with no power applied to a circuit. testing the WSS's with a DMM is a static test. yes power is applied by the DMM battery by setting the DMM in capacitance mode, as it is as well when in resistance mode. voltages (AC or DC) are a passive test.
i dont know the differences between the early and late model WSS's on the E39,as to design and static testing, i know the later ones arent interchangeable with the early ones. another thing ill look in to when i get a chance.
the reason your trans was going in to limp mode when the ABS faulted is that the ABS is no longer sending the road speed info to the trans. im surprised you werent getting a CEL along with a p0500 code.
youre fortunate in having the early ABS unit behind the glove box, in 99 with the advent of the underhood ABS module and its measly protection from the heat of the exhaust manifold, diagnosis of an ABS fault gets more involved, and repair more costly (repair or replacement of the module)
i need to clarify the last line of my previous post....ive rarely seen an e39 ABS system that doesnt have the intermittent interference fault, but it hasnt effected operation of the system nor does it set the ABS, or ASC/DSC light.

[DennisG01]

"Fortunate in having the early ABS"... Yes, no doubt! As I was doing my research on this problem, though, I was confused.... since most of the information out there is about the newer design ABS. I finally stumbled across the info about the earlier ABS and it all started to click. Bluebee's thread was mostly about the newer stuff, with an addendum added for the older stuff. It still wasn't fully "complete" in regards to the older stuff, but it was plenty to get me going. I added my Voltage readings here in this thread to better clarify what someone would see if testing an older system. That's also the reason I titled this thread "Early E39" so maybe, in the future, it will be easier to find for someone.

FYI... Just looked at my DMM again... put it to the capacitance setting (which is the same "dial switch" as resistance, but I can "select" the different mode) and a "V" indicator shows in the display, instead of Omega.