How Do You Tell If ABS Sensor Is going Bad?
 

Hey guys...Sometimes when I press on the brake petal on my 850, I hear the ABS kick in when it's not neccessary. About a month or 2 ago, the one sensor was completely covered with gunk along with the ABS ring and was causing the the ABS to kick on while driving. After cleaning that, it seemed to fix it. I'm just wondering if that sensor may have been damaged with all that gunk or, if it's just going bad.

If the sensor is failing electrically, the ABS light will come on and a specific ABS sensor code code should be present when read with an ODBII reader.

Can you define gunk ? Dust from the road and brake pads accumulating on the sensors is not unheard of and just brushing that off is fine if the sensor does not look like anything has worn through the stainless pad on the bottom.

Dust and oil points to a leaky CV boot but even then the sensor should be fine if all surfaces have been cleaned.

By gunk, well, I pretty much don't know how to describe it. Seemed like dirt and brake pad dust. I'm not getting any ABS light coming on either.

can you tell me where exactly the sensors are? i need to clean mine, no abs or tracs. i've already re-soldered the module speedo works like a charm but wheelspin under acceleration and brake lock-up under hard braking.

maybe if I clean the sensors my abs and tracs would be restored.

The sensors and pick-up rings are behind the rotors, so you have to take to calipers off to access them.

They work on electromagnetic pulses, so the computer is looking for an on-off-on-off-on-off signal. That gunk will prevent the signal and the module will disable the system.

The gunk can be cleaned off with a toothbrush; no need for any chemicals, and to answer the original question, they shoud be fine after a cleaning. Really the only damage that can occur is if a wire gets snipped.

so I can't just access them without taking off the calipers? thanks for the response.

I just read a new brake pad replacement write-up for an S70, all I have to do is remove the 2 x 15mm caliper bolts. How exactly do these sensors look? I'll do this tomorrow if I can't locate them, i'll chime in here with pics.

Thanks

Well this is what happens when your lugs are too tight and you don't have an impact drill...
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using my weight to break the lug, slipped off the factory lug tool twice and took my skin clean off both times. Hopefully this leaves a scar, looks pretty!

Your car is branding you; you are now officially owned by your car...:)

FYI: if you're not going to get a compressor and pneumatic wrenches, get yourself a T-handle lug wrench at least..

Yeah, you'll have to pull the calipers so you can remove the rotor, which is very easy. The caliper is bolted on with two bolts, and it attached to a bracket which is also bolted on with two bolts. Since the bracket "wraps around" the rotor, you'll have to remove it as well.

The pickup cable is mounted next to the brake line, on the left of the picture (this is the front passenger wheel). On the front wheels, it's attached to the strut with a rubber grommet in the middle of the length of cable. In the picture, it has the red plastic clip connecting it to the actual sensor which is mounted on the top of the hub. It's the only rubber tube in the area, where everything else is metal so it's easy to find. It's also easy to damage, so be carefull when swinging the tools!

I can't find a picture of the round pickup plate, but I believe you also have to remove the dust shield, which is three bolts, to clean it up.

thanks, i'll try to knock this out on monday at least.

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did this yesterday, did not have to take off calipers, only took off wheel, the sensor sits right in front of your face.
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just used some pb blaster, small flathead screwdriver, cloth, and a pin to get the gunk out of the sensors themselves. Are there sensors at the rear wheels also?

well, you got it half right. That plastic red/orange plug you disconnected is the wiring harness for the sensor. The actual sensor is mounted in the hub. You can see in your second pic that it's held in place by that lone bolt on top, looking down.

But you have to remove the rotor to clean the (I don't know it's real name) magnetic toothed-disk that the sensor looks for. This disk is probably 5 inches in diameter and where the dust can buildup and prevent the sensor from working properly.

And Yes, the rear wheels have a similar setup. Same as the front in that it'll be the only electrical wires running down to your wheels.

Which I had pics to post, bu for the life of me it appears I never took some of the ABS stuff...

hahaha! i'll tackle this again later in the week. Just came back from the junkyard picked up rear door speakers, deck speakers, glove box door, firewall alarm buzzer, and ashtray for under $20! can't beat the price of junkyards.