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 Post subject: ABS sensor problem
PostPosted: Tue Sep 18, 2018 4:57 pm 
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When replacing the ball joints, one of my ABS sensors on the front wheels was damaged and had to replace it. I first purchased a new ABS sensor and replaced it but the ABS was not working correctly and after braking 2 or 3 times feeling some shaking on the brakes, the ABS light was coming up on the dashboard.
So I replaced the ABS sensor for this SKF BR930224 Hub Unit (https://www.amazon.com/SKF-BR930224-Hub ... automotive) and now every time I reach 40 mph, the ABS light comes up. We scanned it with a Chrysler scanner and the problem seems to be that the speed reading on the wheel that I replaced the sensor is 44 mph while all the other wheels are going at 40 mph. So it seems that this new ABS sensor is sending a different speed information to the ECU than the rest of the wheels and this is causing the ABS light on the dashboard to come up.
What could be the reason to all this and how can I fix it?
Thank you

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 Post subject: Re: ABS sensor problem
PostPosted: Tue Sep 18, 2018 11:14 pm 
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Location: Lebanon, KY, USA
That is totally bizarre.

Here is how they work:

Quote:
DESCRIPTION
Three wheel speed sensors are used. The front sensors are mounted to the steering knuckles. The rear sensor is mounted at the top of the rear axle differential carrier. Tone wheels are mounted to the outboard ends of the front axle shafts. The gear type tone wheel serves as the trigger mechanism for each sensor.
OPERATION
The sensors convert wheel speed into a small digital signal. The CAB sends 12 volts to the sensors. The sensor has an internal magneto resistance bridge that alters the voltage and amperage of the signal circuit. This voltage and amperage is changed by magnetic induction when the toothed tone wheel passes the wheel speed sensor. This digital signal is sent to the CAB. The CAB measures the voltage and amperage of the digital signal for each wheel.


(This is from the 2005 manual, if you have a 2006 it will have four sensors.)

As you see, the "gear type tone wheel serves as the trigger mechanism for each sensor." The sensor is just detecting the teeth on the gear as they move past it. The only way I can see this happening is if there are a different number of "teeth" on the one gear. I suggest you count the teeth on each of the front hubs to make sure they are the same. It seems like the new hub might have more teeth. Or possibly a burr or other defect that makes it look like it has more teeth.

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2005 Liberty Limited CRD; Air Filter Monitor; Samco Hoses; GDE HOT Tune; RL037142AA TC; KJ Interior Rack from All J Products; JBA Adjust-a-strut lift and A-Arms; 245/75R16 Firestone Destination ATs on Moabs; ARB Bumper; ASFIR Skids; FS-2500 Bypass Filter; ARP studs.
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 Post subject: ABS sensor problem
PostPosted: Tue Sep 18, 2018 11:48 pm 
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user113 wrote:
That is totally bizarre.

Here is how they work:

Quote:
DESCRIPTION
Three wheel speed sensors are used. The front sensors are mounted to the steering knuckles. The rear sensor is mounted at the top of the rear axle differential carrier. Tone wheels are mounted to the outboard ends of the front axle shafts. The gear type tone wheel serves as the trigger mechanism for each sensor.
OPERATION
The sensors convert wheel speed into a small digital signal. The CAB sends 12 volts to the sensors. The sensor has an internal magneto resistance bridge that alters the voltage and amperage of the signal circuit. This voltage and amperage is changed by magnetic induction when the toothed tone wheel passes the wheel speed sensor. This digital signal is sent to the CAB. The CAB measures the voltage and amperage of the digital signal for each wheel.


(This is from the 2005 manual, if you have a 2006 it will have four sensors.)

As you see, the "gear type tone wheel serves as the trigger mechanism for each sensor." The sensor is just detecting the teeth on the gear as they move past it. The only way I can see this happening is if there are a different number of "teeth" on the one gear. I suggest you count the teeth on each of the front hubs to make sure they are the same. It seems like the new hub might have more teeth. Or possibly a burr or other defect that makes it look like it has more teeth.


I will take out both front wheels and compare both hubs tomorrow but in the meantime, when I purchased the SKF BR930224 Hub Unit on Amazon, it was saying it was for my 2005 Jeep Liberty 2.8 CRD and I also checked on other sites and they were all saying it was ok for my Liberty. Could this be wrong?
I tried checking on SKF but didnt find information about it...


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 Post subject: Re: ABS sensor problem
PostPosted: Wed Sep 19, 2018 3:52 pm 
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Location: Green Cove Springs FL
Are all your tires exactly the same size?
A tire with a smaller diameter will do more revolutions than the others, making the ABS sensor show a faster speed.

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 Post subject: ABS sensor problem
PostPosted: Wed Sep 19, 2018 4:33 pm 
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flash7210 wrote:
Are all your tires exactly the same size?
A tire with a smaller diameter will do more revolutions than the others, making the ABS sensor show a faster speed.

All my tires are the same size. All 4 tires are just 1/2” taller than the stock tires.


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 Post subject: Re: ABS sensor problem
PostPosted: Thu Sep 20, 2018 8:04 am 
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Before putting this SKF hub unit with its own ABS sensor, I just put a new ABS sensor on the original hub unit but the ABS light on the dashboard was showing up right after the first time I was hitting the brakes. On another post, someone told me to replace the whole hub unit so I did. This gives me the idea that it couldn’t be the SKF hub unit, it has to be something else because with every new ABS sensor I put, it fails...


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