How do you troubleshoot ABS?

[jeryst]

I have a 97 Impreza Outback Sport that has an ABS issue. The ABS comes on on dry roads during breaking, especially at highway speeds or going downhill. The brake pedal gets hard,then there is a click and the pedal pulsates and the car swerves to the right. The ABS light does not come on. Also, I don't know if this is normal or not, but when I press the brake pedal, the automatic transmission disengages, taking away any stopping power due to engine compression. It is extremely scary, and has gotten so bad that I have disconnected the ABS module and have gone back to manual breaking. But I would like to have it operational on icy roads, so I am looking to troubleshoot the system. Local garages have not been very helpful, and I can't afford to take it to a Subaru dealer. How can I determine if it is the ABS module or a wheel sensor, and if it is a wheel sensor, which one?

[idosubaru]

Have you checked the condition of the pads, slides and calipers?

 

Does the ABS light work?

 

With the ABS disconnected everything works perfectly?

 

Usually you just read the codes and it'll tell you where to look or start looking - but you're saying the ABS light works but never illuminates?

Edited January 2, 2017 by grossgary

[jeryst]

The car has new pads, calipers, and rotors for inspection. This behavior started occurring

before everything was replaced, so replacing everything had no effect.

 

The ABS light comes on when the ABS is disconnected, so the light works,

but does not come on when the issue is happening.

 

With the ABS disconnected, everything works normally and the

Issues do not occur.

 

I've had the car hooked up to a code scanner and there were no ABS codes.

The garage told me it's probably an ABS sensor or the ABS unit itself,

but without any codes, they can't say what the problem is.

 

I've searched the site and have seen reference to a couple of taped up

Wires that can be used to generate some ABS codes, but wasn't able to follow

very well as the wires seem to be different for different years, and none

Of the examples were for a 97.

 

I'm looking for a detailed procedure that I can follow to troubleshoot the

system and try to pinpoint the problem because I'm not very mechanically inclined.

[1 Lucky Texan]

what was the condition of the old pads? any sets with uneven wear?

 

were caliper hoses changed?

[jeryst]

I didn't see the condition of the old pads as they were

Changed by the garage doing the inspection.

 

I don't believe any of the brake hoses were changed.

[jeryst]

Can anyone tell me if it is normal for the auto trans to

Disengage when the brake pedal is pressed, on a car with ABS?

[idosubaru]

The abs light not coming on is weird. I've never seen that.

 

Fpr the connector You have to get under there with a light if necessary and look around. All the 95-04's are about the same that I've done so they shouldn't be much different.

 

If you need an abs controller just get a used one. They rarely fail so they're not really worth much.

Www.car-part.com

 

I know something like 1996 legacys had an overactive abs pump or relay. My memory tells me that was 1996 and only when the car was off but you might want to find the Years/models/symptoms to make sure.

[idosubaru]

In order to brake, your foot comes off the gas pedal which closes the throttle plate which is connected to the TPS which is the sensor for driving transmission performance. I'd guess the transmission should do something different when going from pressing the gas pedal to not.

[jeryst]

In order to brake, your foot comes off the gas pedal which closes the throttle plate which is connected to the TPS which is the sensor for driving transmission performance. I'd guess the transmission should do something different when going from pressing the gas pedal to not.

The transmission does not behave like this when the ABS is disconnected, that's why I was wondering if it is normal behavior. With the ABS disconnected,the transmission does not disengage when the brake pedal is pressed.

[sirtokesalot]

the only abs issue ive ever come across so far on these cars is rusted tone rings. i can confirm u can cut a tone ring in the low grooves and then bolt the 2 halfs on the car and it will still function normally. this is how i did mine when my tone ring was bad

[idosubaru]

Brilliant. I would look at those tone rings for sure.

 

What were your symptoms before the repair?

[zmarrott]

pull the sensors from their housing in the knuckles too see if theyre dirty or have foreign objects in there and aroung the tone rings. My friends car had a wheel bearing go bad and it exploded grease and bearing pieces into the tone ring making the car randomly engage abs while braking. No abs light or code either

[sirtokesalot]

Brilliant. I would look at those tone rings for sure.

 

What were your symptoms before the repair?

 with the rusted tone ring the abs was overactive and kicking the pedal back at me even when pavement was dry. no abs light.

 

pull the sensors from their housing in the knuckles too see if theyre dirty or have foreign objects in there and aroung the tone rings. My friends car had a wheel bearing go bad and it exploded grease and bearing pieces into the tone ring making the car randomly engage abs while braking. No abs light or code either

 

 good luck if its rusty like these cars normally are you wont get the sensor out in one piece to check for debris on the sensor you will likely have to take the rotors off.

Edited January 15, 2017 by sirtokesalot