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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Technical Forums > Mechanical Maintenance: Break-in / Oil & Fluids / Servicing / Warranty > Rear wheel abs issue



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      01-19-2015, 08:24 PM   #1
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Rear wheel abs issue

My abs/traction control/brake lights came on this weekend while driving down the highway. The lights turn off after driving a short distance after each start up, but all come back on once I hit about 20 mph.

I took it to my mechanic this afternoon, and he pulled the codes as a period error of the exciter ring, code 5db2.

We switched the right and left sensor to see if the error followed the sensor, but it didn't. It stayed on the same wheel. So we were looking, and it appears the abs ring is integrated with the wheel bearing. Is that correct?? I have not noticed any wheel bearing-like issues, besides the abs reading issue.

Is it possible for just the abs part of the bearing to fail?
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      01-20-2015, 05:32 AM   #2
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Seems strange being that the ring is attached to the bearing and inside the hub assembly where there is nothing to damage it. You could inspect it through the sensor hole to check if there is tooth missing. I'd suspect the problem lies somewhere in the harness that leads to the wheel speed sensor because the problem does not follow the sensor. It could be a rodent chewed up the wiring harness somewhere after the connector. I'd trace the harness as far as I could (take the wheel line out), or take it to the dealer and have an electrical test done on the harness. If it is damaged by a rodent, your comprehensive insurance should cover the diagnosis and repair.
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      01-20-2015, 01:24 PM   #3
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Quote:
Originally Posted by Efthreeoh View Post
Seems strange being that the ring is attached to the bearing and inside the hub assembly where there is nothing to damage it. You could inspect it through the sensor hole to check if there is tooth missing. I'd suspect the problem lies somewhere in the harness that leads to the wheel speed sensor because the problem does not follow the sensor. It could be a rodent chewed up the wiring harness somewhere after the connector. I'd trace the harness as far as I could (take the wheel line out), or take it to the dealer and have an electrical test done on the harness. If it is damaged by a rodent, your comprehensive insurance should cover the diagnosis and repair.
It seems the wheel bearing has a magnetic component inside one of the bearing seals. I don't know how it can "go bad" but it seems to not be a completely unusual occurrence judging by the number of other posts I see about it.
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      01-20-2015, 08:18 PM   #4
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Quote:
Originally Posted by davidwarren View Post
It seems the wheel bearing has a magnetic component inside one of the bearing seals. I don't know how it can "go bad" but it seems to not be a completely unusual occurrence judging by the number of other posts I see about it.
So it's called a Hall-Effect transducer, which means it generates a magnetic pulse in the speed sensor as the peaks and valleys of the "toothed" ring-wheel passes by the sensor. If a tooth were broken off the ring-wheel it would affect the pulse generation, but I doubt the ring-wheel is broken, which is why I think there is break somewhere in the harness past the connector for the speed sensor.
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      01-20-2015, 09:13 PM   #5
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Quote:
Originally Posted by Efthreeoh View Post
So it's called a Hall-Effect transducer, which means it generates a magnetic pulse in the speed sensor as the peaks and valleys of the "toothed" ring-wheel passes by the sensor. If a tooth were broken off the ring-wheel it would affect the pulse generation, but I doubt the ring-wheel is broken, which is why I think there is break somewhere in the harness past the connector for the speed sensor.
Right, I'm familiar with how the "toothed gear" works. And I agree it would be unusual for that to be an issue. But apparently, rather than the traditional toothed abs gear, the e90s have a magnetic ring in the wheel bearing. (See the black ring on the outside of the bearing here- http://c1552172.r72.cf0.rackcdn.com/246569_x800.jpg)

After reading a number of threads where the dealer changed the bearing, I guess that is the fix for it. We did inspect the visible part of the wiring, and it was all fine. Also, we could read live data when it was connected to the computer.

I am going to get an appointment at the dealer this week to check it out. If it is the bearing, it should be covered by my cpo.
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      01-21-2015, 05:07 AM   #6
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I've not replaced a rear bearing in an E90, but I do know from reading the procedure that it needs to be installed in the correct orientation, meaning the "magnetic" ring must face inside. I have replaced a front hub (bearing) and it does use a traditional toothed gear/hall effect setup. Not being familiar with the specific design of the rear bearing, it could be that BMW just uses the actual ball bearings (evenly spaced in the bearing cage) as the "teeth" of a traditional wheel speed sensor setup. I would expect that the "magnetic" side of the bearing that needs to face the transducer is just that the seal is magnetically transparent so the transducer can detect the ball bearings. Now if the bearing is starting to fail, where the ball bearing cage has broken and the balls are no longer evenly spaced, that would cause a malfunction of the wheel speed sensor.

If you've got CPO, then I'm not sure why you took it some other place first.

Good luck with it.
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      02-05-2015, 09:51 PM   #7
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Finally got this fixed up. It was just my rear bearing.
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      02-08-2015, 06:30 AM   #8
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So, I had my car on the lift yesterday for an oil change. I've really never looked at the rear hubs much since I've not had a problem with them. But yesterday, with this thread in mind, I closely looked at the hubs and halfshafts to check for CV boot tears, and I noticed that the hub does have a hall effect tooth ring built into it. From the position of where the wheel speed sensor is located, the sensor is nowhere near the back side of the wheel bearing and appears to "look" right at the tooth ring. So was your bearing going bad and just affecting the speed sensor?
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      02-08-2015, 07:16 AM   #9
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Quote:
Originally Posted by Efthreeoh View Post
So, I had my car on the lift yesterday for an oil change. I've really never looked at the rear hubs much since I've not had a problem with them. But yesterday, with this thread in mind, I closely looked at the hubs and halfshafts to check for CV boot tears, and I noticed that the hub does have a hall effect tooth ring built into it. From the position of where the wheel speed sensor is located, the sensor is nowhere near the back side of the wheel bearing and appears to "look" right at the tooth ring. So was your bearing going bad and just affecting the speed sensor?
Perhaps the first year e90s have a toothed ring, but later models have the component in the hub bearing.

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      12-09-2018, 01:04 PM   #10
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So I’ve got a 5db2 and the abs and tire monitor aren’t working according to the I-Drive. Most of the stuff I’ve read seems to indicate that it’s the wheel bearing. It seems like there’s a slight possibility it’s the sensor...has anyone solved this by changing the sensor?
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      12-10-2018, 11:09 AM   #11
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Quote:
Originally Posted by Bimmer_Engineer View Post
So I’ve got a 5db2 and the abs and tire monitor aren’t working according to the I-Drive. Most of the stuff I’ve read seems to indicate that it’s the wheel bearing. It seems like there’s a slight possibility it’s the sensor...has anyone solved this by changing the sensor?
So about a year after my last reply in this thread, I lost the left rear wheel speed sensor. I replaced it and all was well. A few months later, the same speed sensor came up lame again. Further investigation showed the face of the sensor was rubbing against the ABS toothed ring. So with the second sensor I mounted it about 0.75MM farther away from the toothed ring. Did just used a small washer on the mounting bolt under the body of the sensor between it and the wheel hub. It raised it enough to keep the sensor from contacting the ring.

About a year later I discovered why there was contact between the ring and the sensor. The ring being iron (for good magnetic properties) had corroded really bad, grew in size, and was rubbing on the face of the sensor. I discovered this when I was replacing the rear wheel bearings. The ABS ring is fixed to the outboard CV joint housing and it sits just inside of the back of wheel hub where the axleshaft enters. The left axle was rusted all to hell and fused with the splines in the hub flange, so I had to replace the shaft anyway. With the new shaft in place and its new ABS ring, I remounted the speed sensor back in its original position. It's been good ever since.
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      12-10-2018, 01:12 PM   #12
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Quote:
Originally Posted by Efthreeoh View Post
So about a year after my last reply in this thread, I lost the left rear wheel speed sensor. I replaced it and all was well. A few months later, the same speed sensor came up lame again. Further investigation showed the face of the sensor was rubbing against the ABS toothed ring. So with the second sensor I mounted it about 0.75MM farther away from the toothed ring. Did just used a small washer on the mounting bolt under the body of the sensor between it and the wheel hub. It raised it enough to keep the sensor from contacting the ring.

About a year later I discovered why there was contact between the ring and the sensor. The ring being iron (for good magnetic properties) had corroded really bad, grew in size, and was rubbing on the face of the sensor. I discovered this when I was replacing the rear wheel bearings. The ABS ring is fixed to the outboard CV joint housing and it sits just inside of the back of wheel hub where the axleshaft enters. The left axle was rusted all to hell and fused with the splines in the hub flange, so I had to replace the shaft anyway. With the new shaft in place and its new ABS ring, I remounted the speed sensor back in its original position. It's been good ever since.
Thanks for the feedback...the sensor is only $20 and I won't be able to have time work on it for nearly 2 weeks so i'm just gonna go ahead and order one and cross my fingers. If it's the wheel bearing i'll cross that bridge later...

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      12-10-2018, 03:17 PM   #13
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Originally Posted by Bimmer_Engineer View Post
Thanks for the feedback...the sensor is only $20 and I won't be able to have time work on it for nearly 2 weeks so i'm just gonna go ahead and order one and cross my fingers. If it's the wheel bearing i'll cross that bridge later...
When you pull the old sensor, look at the face of it very closely for scratch marks. If the plastic breaks the hermetic seal and the sensor gets wet inside it will not work until it gets dry again.
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      12-10-2018, 04:53 PM   #14
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That may be what happened...it happened first during a torrential downpour...
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      12-22-2018, 01:57 PM   #15
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So I went to swap out the sensor yesterday and I don’t have the right sensor. Since I had the car jacked up I decided to swap the sensors and see what difference it makes. No codes yet so I’m hoping it’s a short in the sensor rather than a bad wheel bearing. Will see when I rains next time...
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