ABS engages unnecessarily - 95 Leg Sedan AWD

[mikeamondo]

Hi Guys...  been a while!   My daughter's 95 Legacy Sedan has a strange ABS issue....  when you first start out from park, it can engage...  sound and brake pulsing just like you'd hear while on ice.  It only lasts a second or two then quits.  Also, as you come to a gentle stop, it will come on for a second....  and, my daughter has reported that during a hard deceleration from 50 mph or so, it will kick on in the same manner, and if feels as though the car is not slowing while it's engaged.   The car is in Colorado and I'm in WV.   We visited this weekend, and I test drove the car, but the traffic was too heavy for me to replicate the higher speed symptom.  

I couldn't find any direct posts here (I'm sure there are, but the search terms are highly varied) ....  On another site, I found a thread about later cars... 98 and 04 ... that indicated sensor issues and something called a 'tone ring' .... which I am unfamiliar with.

I'm going to have her take it to a Subie guy there, but I wanted to get some info from the experts here, first, so I can have a semi-intelligent conversation with him about the issues via phone.

As always, thanks in advance for your help!

Mike

[1 Lucky Texan]

I think early ABS had an issue with a relay or something buzzing, but this seems different, like a bad wheel sensor or a wire/connector that's intermittent.

 

 

 

[GeneralDisorder]

That's going to be a bad wheel speed sensor. 

GD

[idosubaru]

Hey mike!  The tone ring is the ring that has "teeth" that the wheel speed sensor are "looking at".  on a 95 the teeth are part of the hub (newer models they're intergrated into the axles). 
If you find the wheel speed sensor - the only wire going to the knuckle - the tone ring will be just millimeters away from the sensor tip, which may or may not be visible without removing the wheel. 

1.  clean the wheel speed sensors - they get dirty or debris on them and can get flaky.  there's one at each wheel poking through the rear of the dust plate/knuckle.
Have to pull the

2. look for warn/damaged ABS wheel speed sensors.  or replace the faulty one - there is a way to do a self-test of the ABS system where the light blinks the code and tells you which sensor is bad...if it's registering as bad, yours sounds intermittent. 

3.  some 90's models had flaky ABS pump relays that would cause noises even when the car was off - doesn't sound like your issue but worth noting as you trouble shoot. 

Edited August 28, 2018 by idosubaru

[1 Lucky Texan]

^^^^ yeah, metal or rusty debris on the sensor might cause intermittent operation - good post

[Suzam]

Check the tires and pressure are up to specs. I once had a low tire cause the ABS to activate during braking.

As  I recall there's a self check when you first start up the MY95 ( and similar years) for the ABS. The pump runs briefly which is normal.

[idosubaru]

1 hour ago, Suzam said:

Check the tires and pressure are up to specs. I once had a low tire cause the ABS to activate during braking.

As  I recall there's a self check when you first start up the MY95 ( and similar years) for the ABS. The pump runs briefly which is normal.

In the same way - terribly cracked/sun scorched/old tires can cause the ABS to blip unecessarily usually in poor traction conditions.  i've seen nearly full tread tires do it that were baked in the florida sun. 

[coryl]

A poorly calibrated, sticking or failing brake light sensor can also play with ABS/traction control when braking and set off codes. Have you checked the codes when this happens? Clearly a code will be detected when there's a fault like this so that's where they need to analyze when you get to the shop. It will be fairly easy to figure out the issues when they check the codes.

Good luck and let us know what you find out.

[mikeamondo]

Guys.... thanks for all the great tips....  this and other reading leads me to think the issue is the speed sensor ... or rather one of them.  I'll pass the info on to my daughter and we'll most likely get the car to a repair shop....    been a crazy few weeks...  just realized I posted this a month ago!