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Old 10-17-2009, 11:48 PM   #1
kirbykirb
Scooby Newbie
 
Member#: 183596
Join Date: Jul 2008
Chapter/Region: South East
Location: USA
Vehicle:
2005 WRX/9-2x
Obsedian Black Pearl

Default ABS light on, what sensors trigger it? wheel ABS sensor, speed sensor, what else?

Besides a ABS failure, just talking about sensors, what sensors trigger it?

I want to replace all the sensors which this goes goes to, I need to replace both speed sensors (only know where one is though, the one on the tranny, no idea of #2) and the 4 wheel ABS sensors too..

what else
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Old 10-18-2009, 10:43 PM   #2
Jonathan
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Member#: 4021
Join Date: Feb 2001
Chapter/Region: NESIC
Location: Natick, MA USA
Vehicle:
1999 Legacy GT Ltd
Quick Silver Metallic

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Next to each of your wheel hubs is an "inductive pickup". These things sense the motion of the "tone wheel" located on each of your axle joints (The ends of each axle has what is known as a "constant Velocity" or "CV" Joint). The "Tone Wheel" is basically just a small metal band of what look like gear teeth. Over time these things can rust, get bumped or even crumble in to pieces and eventually just plain fall off.

Basically when the car knows it is motion and cant get a signal from any one or more of these "inductive pickup" devices and the brakes aren't being applied it figures that something is wrong. These "tone wheel" things are cheap. I would try replacing them first if you can. If you have to replace all four CV axle assemblies then maybe they aren't so cheap after all.

The ABS system functions in a nut shell by monitoring each of the four signals generated by these tone wheels and if the car is in motion, and one (or more) of these inductive pickups stops getting a signal when the brakes are applied, then the ABS assumes that one (or more) wheels have locked up and it "pumps" brakes on all four wheels very rapidly.

Someone please correct me if I am spreading incorrect information.
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Old 10-22-2009, 03:27 PM   #3
jey
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Member#: 32503
Join Date: Feb 2003
Chapter/Region: TXIC
Location: Johnson City, TX
Vehicle:
2011 Tribeca
1995 Legacy Wagon

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Both speed sensors are on the tranny - one in the back, one in the front.
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Old 10-23-2009, 05:31 AM   #4
iluvdrt
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Member#: 46248
Join Date: Oct 2003
Chapter/Region: RMIC
Location: DRTY Autosports Denver, Co
Vehicle:
2012 outback 2.5
sky blue

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Quote:
Originally Posted by jey View Post
Both speed sensors are on the tranny - one in the back, one in the front.
I think you are refering to the vehicle speed sensor, not the wheel speed sensor.

With the 4 channel ABS you have a sensor at each wheel that reads the wheel speed> 5 mph IIRC. If anyone of those sensors fails your ABS light will be illuminated. You will need a scanner that reads ABS to verify which one is bad.

A lot of times when these lights come one there is just too much brake dust stuck to the sensor (It is a magnet) and the sensor can no longer read the exciter ring.

Pull all 4 brakes and rotors and check the sensors. If one or more is full of little metal things clean it off with brake cleaner, reset battery and drive. You will know as soon as you break the 5 mph mark wether or not it is fixed.
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Old 06-19-2010, 10:37 PM   #5
kirbykirb
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2005 WRX/9-2x
Obsedian Black Pearl

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Quote:
Originally Posted by iluvdrt View Post
I think you are refering to the vehicle speed sensor, not the wheel speed sensor.

With the 4 channel ABS you have a sensor at each wheel that reads the wheel speed> 5 mph IIRC. If anyone of those sensors fails your ABS light will be illuminated. You will need a scanner that reads ABS to verify which one is bad.

A lot of times when these lights come one there is just too much brake dust stuck to the sensor (It is a magnet) and the sensor can no longer read the exciter ring.

Pull all 4 brakes and rotors and check the sensors. If one or more is full of little metal things clean it off with brake cleaner, reset battery and drive. You will know as soon as you break the 5 mph mark wether or not it is fixed.
Found the problem, the rear brake sensor driver side got cut, it was cut as if it was by a sharp object so it was intentional.

I'm going to trace the connector, I think it's on the sensor side and not where it plugs up into the car (hopefully.)

So basically this weekend:

Investigate speed sensor issue.
Oil change
Thermostat (may have to wait though until it comes in.)
Coolant
Spark plugs
Spark wires (they seem okay for now so we'll see)

And see why my fans don't come on properly...
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