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Discussion Starter #1
2004 XC90. The ABS light has been flashing for months and I finally got VIDA and a DiCE unit to diagnose. It's reporting "BCM-0012: Left front wheel sensor. Faulty Signal." I've taken the sensor out and cleaned it. There was some wear on the bottom of the sensor from where it scraped on the pulse wheel but didn't look bad. The teeth on the wheel seem to be ok but not sure how good they need to look. Using VIDA I can see that the BCM-Velocity is being read ok and looks consistent with the right wheel velocity. I'm assuming the ABS sensors are used for that reading, right? I clear the code and it comes right back on the next test drive.

My main question: Is there a way to definitively tell what part is bad? I'd hate to change out the pulse wheel if that's not the problem, and same for the sensor. Has anyone seen a bad/flaky BCM act like this?
 

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Discussion Starter #2 (Edited)
Looks like it is a broken tooth on the pulse wheel. When I first looked at it yesterday I did a quick spin of the axle but it was bugging me that I didn't look close enough so I hooked up the DiCE and got the velocity reading in the image below. The dips in the graph are a missing tooth. Everytime that gap passed the sensor there was a dip in the graph.

If anyone had tips on removing that pulse wheel (reluctor ring) for a front left axle or a good source for them let me know.


 

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Just to complete this thread for future repairers, here's the final status of the fix. A new reluctor, tone ring, pulse wheel, or whatever you want to call it was ordered from UK Parts Direct for about $25US including shipping and got here in about a week. The steps to do the repair:

- Block the car wheels and put the car in neutral so that you can spin the axle by hand later.
- Jack up left front wheel and remove it.
- Remove ABS sensor and hang out of the way.
- Remove the 2 big strut bolts. This will allow swinging the hub assembly out of the way so you can pull the axle out of the hub.
- Loosen the axle bolt and tap gently to get the axle moving back out of the hub.
- Pull the axle from the back of the hub and prop it up using a 2x4 between it and the lower control arm to put the axle end above the brake disc.
- Remover the old reluctor. This should be easy if it is cracked. My came off by hand.
- Clean the surface where the reluctor was using a wire brush, files, or whatever. Mine was extremely corroded, but files and then a brush did the trick. Spin the axle to make sure it is cleaned all around.
- Heat the new reluctor to a blue color using a plumbers torch or similar. Takes a couple of minutes.
- Put the hot reluctor on the axle using pliers and gently but quickly tap it in place. Use a drift (metal or hard wood) to seat it.
- Let it cool for a couple of minutes.
- Put everything back in place by reversing the above procedure.
- Clear the ABS codes with VIDA.
 

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Just to complete this thread for future repairers, here's the final status of the fix. A new reluctor, tone ring, pulse wheel, or whatever you want to call it was ordered from UK Parts Direct for about $25US including shipping and got here in about a week. The steps to do the repair:

- Block the car wheels and put the car in neutral so that you can spin the axle by hand later.
- Jack up left front wheel and remove it.
- Remove ABS sensor and hang out of the way.
- Remove the 2 big strut bolts. This will allow swinging the hub assembly out of the way so you can pull the axle out of the hub.
- Loosen the axle bolt and tap gently to get the axle moving back out of the hub.
- Pull the axle from the back of the hub and prop it up using a 2x4 between it and the lower control arm to put the axle end above the brake disc.
- Remover the old reluctor. This should be easy if it is cracked. My came off by hand.
- Clean the surface where the reluctor was using a wire brush, files, or whatever. Mine was extremely corroded, but files and then a brush did the trick. Spin the axle to make sure it is cleaned all around.
- Heat the new reluctor to a blue color using a plumbers torch or similar. Takes a couple of minutes.
- Put the hot reluctor on the axle using pliers and gently but quickly tap it in place. Use a drift (metal or hard wood) to seat it.
- Let it cool for a couple of minutes.
- Put everything back in place by reversing the above procedure.
- Clear the ABS codes with VIDA.
Thanks for the writeup!
 

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Discussion Starter #6
Nice work on the diagnosis and the home repair. Do you have any idea what caused the tooth to be broken?
I think what looked like a broken tooth was really the break in the ring itself. The corrosion must have weakened it and the rust underneath probably just popped it. It sure made getting the old ring off easy.
 
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