ABS issues

My 1999 suburban has some braking issues. When braking the abs often activates when I am nearly stopped. It is like it is not seeing a sensor or something. It only does it at slow speed.

How does the abs work? What conditions have to exist to ativate the abs motor? Brake pedal actuated and missed sensor signal (locked wheel)? What does the sensor pick up on the front wheels? rear wheels?

I intent on replacing pads and shoes (rotors and drums if nec) but I am afraid that this may not even be part of the problem.

Anyone have similar experiences?

My 1999 suburban has some braking issues. When braking the abs often activates when I am nearly stopped. It is like it is not seeing a sensor or something. It only does it at slow speed.

How does the abs work? What conditions have to exist to ativate the abs motor? Brake pedal actuated and missed sensor signal (locked wheel)? What does the sensor pick up on the front wheels? rear wheels?

I intent on replacing pads and shoes (rotors and drums if nec) but I am afraid that this may not even be part of the problem.

Anyone have similar experiences?

Therre 's a TSB http://www.aboutautomobile.com/tsb/1997/CHEVROLET/SUBURBAN
7 TSB No.: 020525006 NHTSA No.: 10000062 TSB Date: January 01, 2006
Failing Component:
Service Brakes, Hydraulic:Antilock

Description of Summary:
Antilock brake (abs) activation at low speeds.
8 TSB No.: 020525006A NHTSA No.: 10000749 TSB Date: December 01, 2002
Failing Component:
Service Brakes, Air:Antilock

Description of Summary:
Antilock brake (abs) activation at low speeds on various models including the 1995 and 1996 envoy.

Known GM problem.
There is no fault code in the OBD ABS.
At low speed your car will NEVER STOP because abs activation.
Very very dangerous on traffic light for exemple ! ! !

Fix :
You must test abs sensor voltage.
If it's too low clean for debris or rust or replace both l&r sensor.
Else you will change the wheel hub.

My advice :
While the problem is not fixed silmply unplug abs wiring from one sensor.
It will light ON the abs light on dash.
ABS sytem will be disconnected.

NO ABS but less dangerous IMHO.

Christophe.

My 1999 suburban has some braking issues. When braking the abs often activates when I am nearly stopped. It is like it is not seeing a sensor or something. It only does it at slow speed.

How does the abs work? What conditions have to exist to ativate the abs motor? Brake pedal actuated and missed sensor signal (locked wheel)? What does the sensor pick up on the front wheels? rear wheels?

I intent on replacing pads and shoes (rotors and drums if nec) but I am afraid that this may not even be part of the problem.

Anyone have similar experiences?


It is best to get it on a ABS capable scanner and see where the problem is.
You can watch speed sensor reading on a scanner and make sure all 3 or 4 sensors match in mph reading.
Also check for codes when abs light is on or before turning ign off after it does it.
Get code and post back code no.
Speed sensors tell the ABS system what the wheels or doing or if one is spinning or locking up..
A bad speed sensor or wiring will kick on abs system,

Remove wheel, brake caliper, rotor to get to the wheel speed sensor. ( I am not sure if 99's have a shield behind the hub that requires to be removed or not to access sensor).

Remove hex head bolt and carefully remove sensor. Huge possiblity that there is rust on the sensor housing and hub area. Plug hole so contaminates do not get into hub assembly and clean both surfaces with wire brush.

Apply grease to surface of hub and sensors and reinstall.

Here is a site that gives you procedure for testing wheel speed sensors, this is for up to 98 vehicle but I would think it should apply to 99 also:
http://www.autozone.com/az/cds/en_us/0900823d/80/08/84/90/0900823d80088490/repairInfoPages.htm

Hope this helps

Resistnce tests are a 50% diagnosis at best, monitoring direct sensor inputs to the ebcm is the proper method no guess work way to do this, as MT2500 said.

Did any of these solutions fix your original issue. I also have a '99 Sub and it has started doing the exact same thing about 2 months ago. I have put new front discs, pads, hoses, master cyl., rear rotors, drums and lines on and it still is doing it. (grrrr) Any input as to how you solved yours would be great!

Thanks,

Did any of these solutions fix your original issue. I also have a '99 Sub and it has started doing the exact same thing about 2 months ago. I have put new front discs, pads, hoses, master cyl., rear rotors, drums and lines on and it still is doing it. (grrrr) Any input as to how you solved yours would be great!

Thanks,

Unfortunately for you, this is not a mechanical problem but electrical.

Go to HTTP://WWW.SAFERCAR.GOV.

Select your car/year etc.
You get :

Recalls Summary

Make / Models : Model/Build Years:
CHEVROLET / AVALANCHE 2002
CHEVROLET / SILVERADO 1999-2002
CHEVROLET / SUBURBAN 2000-2002
CHEVROLET / TAHOE 2000-2002
GMC / SIERRA 1999-2002
GMC / YUKON 2000-2002
GMC / YUKON XL 2000-2002
Recall Number: 05V379000
Summary:
CERTAIN PICKUP TRUCKS AND SPORT UTILITY VEHICLES MAY EXPERIENCE UNWANTED ANTILOCK BRAKE SYSTEM (ABS) ACTIVATION. THIS CONDITION IS MORE LIKELY TO OCCUR IN ENVIRONMENTALLY CORROSIVE AREAS. THIS RECALL WILL BE LAUNCHED IN THE "SALT BELT" STATES OF CONNECTICUT, DELAWARE, ILLINOIS, INDIANA, IOWA, MARYLAND, MASSACHUSETTS, MAINE, MICHIGAN, MINNESOTA, MISSOURI, NEW HAMPSHIRE, NEW JERSEY, NEW YORK, OHIO, PENNSYLVANIA, RHODE ISLAND, VERMONT, WEST VIRGINIA, WISCONSIN AND THE DISTRICT OF COLUMBIA ONLY.
Consequence:
THIS CAN CAUSE INCREASED STOPPING DISTANCES DURING LOW-SPEED BRAKE APPLICATIONS, WHICH COULD RESULT IN A CRASH.
Remedy:
DEALERS ARE TO REMOVE THE WHEEL SPEED SENSOR AND THOROUGHLY CLEAN THE WHEEL SPEED SENSOR MOUNTING SURFACE ON THE BEARING, APPLY RUST INHIBITOR TO THE CLEANED SURFACE, GREASE THE MOUNTING SURFACE, REINSTALL THE WHEEL SPEED SENSOR, AND CHECK THE PEAK-TO-PEAK OUTPUT VOLTAGE TO ENSURE THE WHEEL SPEED SIGNAL IS WITHIN SPECIFICATIONS. THE RECALL BEGAN SEPTEMBER 22, 2005. OWNERS MAY CONTACT CHEVROLET AT 1-800-630-2438 OR GMC AT 1-866-996-9463.
Notes:
GM RECALL NO. 05068. GM REVISED THE INVOLVED VEHICLES BY AMENDING THE ORIGINAL 573 REPORT ON OCTOBER 4, 2005. GM REVISED THE ORIGINAL 573 REPORT ON DECEMBER 16, 2005, TO INCLUDE ADDITIONAL STATES AND VEHICLE POPULATION. CUSTOMERS MAY ALSO CONTACT THE NATIONAL HIGHWAY TRAFFIC SAFETY ADMINISTRATION'S VEHICLE SAFETY HOTLINE AT 1-888-327-4236 (TTY 1-800-424-9153), OR GO TO HTTP://WWW.SAFERCAR.GOV.

There is a lot of PDF document regarding this issue:
Check this out first:

http://nhthqnwws111.odi.nhtsa.dot.gov/acms/docservlet/Artemis/Public/Recalls/2005/V/RCRIT-05V379-3476.pdf
http://nhthqnwws111.odi.nhtsa.dot.gov/acms/docservlet/Artemis/Public/Recalls/2005/V/RCRIT-05V379-9258.PDF
http://nhthqnwws111.odi.nhtsa.dot.gov/acms/docservlet/Artemis/Public/Recalls/2005/V/RCMN-05V379-8240.PDF
http://nhthqnwws111.odi.nhtsa.dot.gov/acms/docservlet/Artemis/Public/Recalls/2005/V/RCRIT-05V379-6740.PDF
http://nhthqnwws111.odi.nhtsa.dot.gov/acms/docservlet/Artemis/Public/Recalls/2005/V/RCMN-05V379-8208.PDF

Christophe Salvaing

This has been around for a while as you can see, the issue, whether it is part of recall or not, still requires diagnosis.

My 1999 suburban has some braking issues. When braking the abs often activates when I am nearly stopped. It is like it is not seeing a sensor or something. It only does it at slow speed.

How does the abs work? What conditions have to exist to ativate the abs motor? Brake pedal actuated and missed sensor signal (locked wheel)? What does the sensor pick up on the front wheels? rear wheels?

I intent on replacing pads and shoes (rotors and drums if nec) but I am afraid that this may not even be part of the problem.

Anyone have similar experiences?
I have 30 years experience with speed sensors on transportation vehicles. the problem you are experiencing is most likely as mentioned by a fellow member rust has caused the sensor to move . if sensor clearance is increased the slightest amount voltage produced will be too low. at slow speeds the sensor produces a small voltage as speed increases voltage increases thats why its acting up at slow speeds now, as time passes it will fail at higher speeds. I don't know your abilitys or equiptment you may have but I would jack front wheels off ground remove speed sensor connector hook MV voltmeter to sensor terminals spin wheel, the sensor with the lowest voltage is the problem, resistance is not to be considered here. don't replace any brake parts as this will not fix your problem.........not too difficult. if rust is excessive under rotors use care to clean rust with a small tooth brush like wire detail brush around sensor then remove sensor and use file to smooth surface. after reinstalling sensor I use a fast drying high temp antisieze compound over the metal this will dry in 30sec. not the paste antisieze as most are familiar with. if time permits you should do both sides as this is a common problem whenever i work on the brakes i clean and spray this area and so far no failures here......

This worked for my Freelander V6 2001, after the garage in Barbados spent weeks trying to find a solution. Also wasted money replacing a very expensive ABS module that did not solve the problem....I found this site and forwarded reference to garage...It Worked....thanks guys.

This fixed the problem on my 95 burb with 208,000 miles..... while I was there I also used performance slotted rotors from NAPA..... the best brakes i have had in a long time if ever.......

cleaning the rust off the hub worked for me. i used a file.

cleaning the rust off the hub worked for me. i used a file.

In the post I made in 2007 I did not mention the other problem with this speed sensor / hub assy.

the hub bearing when failing will cause this failure. the grease gets filled with rusted metal and is attracted to the magnetic sensor.

the hub grease seals rust out. this is because they are no longer made from corrosion resistant metal as was the case years ago.

GM should be held responsible for crashes due to this failure since the design change saved them money and now this widespread designed failure is causing a dangerous operating condition.

both OEM hub bearings the grease seals failed .all that was left was the rubber and some rusted metal.