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Old 02-19-2013, 08:03 AM
HTK12 HTK12 is offline
Officially Welcomed to the 'Fest
Location: Finland
Join Date: Aug 2012
Posts: 1,225
Mein Auto: E39 540i
Originally Posted by Flybot View Post
One month followup on the intermittant ABS/ASC light.

I was initially getting the two mentioned lights and they would go out either at random, or sometimes if I turned the wheel from lock to lock. This degraded in to the transmission not automatically shifting in to 3 or 4. If this happens, you can manually shift up by clicking the shifter from D to 3. Downshifting is still automatic. Anyway, I thought initially it was the steering angle sensor because it could sometimes get it to go away by turning the wheel. I wanted to do the diode check on the wheel speed sensors using Bluebees thread but I have the older ABS System ('98 528) and the pin outs dont match up. I found this thread with the pin outs for the older ABS system:

Anyway, I changed out the left front sensor, which was literally crumbling apart. When tested, I got zero volts on the diode test and 3k ohms. It was supposd to be .5-2M ohms, according to the M3 thread. I cut the cable of the old sensor to do some further investigation and found that it had a small cut in the outer black insulation. The inner yellow/red wires were crumbling apart just touching them, and the copper was actually green from corrosion.

So as with all intermittent issues, it is fixed- until it isnt. The left front sensor was without a doubt bad, and I havnt had any errors since changing it out. I still dont see how the one sensor went from ABS/ASC error to then later include the transmission. Im keeping my fingers crossed.

This wheel speed sensor clearly gave its all and will receive full honors as it is laid to rest in the trash can.
If you google you'll find out that many transmission issues are caused by wheel speed sensors. Transmission needs that sensor information to do the shifting, if the transmission is now shifting smootly there is no reason to worry.
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