I have a chevy 2000 with the hydro boost braking system. the truck is a 2500 with a 6.0 gasser in it. When you apply the brakes at 50 MPH all is fine as you slow down to 5 MPH the abs brakes go on and the brake petal sinks toward the floor. Low speed stops get a little tough. I put a scanner on the truck, (snap-on) there are no codes for the braking system and the abs lights, or brake light do not come on when the abs goes on. The scanner did say the truck was going 3 MPH when it was parked in the driveway. This truck has had new tires, the other owner must have put them on and they are larger then the orginal tires that came with the truck. I do not know where to go from here, do any of you experts have any idea of what could be wrong?


Thanks for the help......

Different gears, too? Or just different wheel size?



Dennis

The truck ran fine for 1 year, with the same tires on it. it just started this the other day. Tires are the same size all the way around and the frt and rear diff. are factory.....

seems like I remember someone else had a problem with ABS recently and
the problem was dirty sensors or something. Do a search for ABS
and see what happens. . .



Good Luck,

Dennis

Did, the search there was one post about the sensors getting dirty or rusty. will put in up on the lift and take a look this week. will let you know how I make out. Thanks....

<H1>Antilock Brake (ABS) Activation at Low Speeds (Clean Wheel Speed Sensor Mounting Surface) #03-05-25-007A - (Sep 3, 2004)</H1>


</TABLE>Antilock Brake (ABS) Activation At Low Speeds (Clean Wheel Speed Sensor Mounting Surface)


2002-2004 Cadillac Escalade, Escalade EXT


2003-2004 Cadillac Escalade ESV


1999-2004 Chevrolet Silverado


2001-2004 Chevrolet Suburban, Tahoe


2002-2004 Chevrolet Avalanche


2003-2004 Chevrolet Express


1999-2004 GMC Sierra


2001-2004 GMC Yukon, Yukon XL


2003-2004 GMC Savana


2003-2004 HUMMER H2





This bulletin is being revised to update the correction information. Please discard Corporate Bulletin Number 03-05-25-007 (Section 05 -- Brakes).<A name=ss1-1548756><A href="http://service.gm.com/servlets/BlobShtml?ShtmlFile=1548756&amp;pubid=147#ss1-1548756" target="_blank">
<H5>Condition</A></H5>





Some customers may comment on ABS activation at low speeds, usually below 8 km/h (5 mph). Upon investigation, the technician will find no DTCs set.<A name=ss2-1548756><A href="http://service.gm.com/servlets/BlobShtml?ShtmlFile=1548756&amp;pubid=147#ss2-1548756" target="_blank">
<H5>Cause</A></H5>


The cause of this condition may be an increased air gap between the wheel speed sensor and the hub reluctor ring due to rust and debris built up on the sensor mounting surface.<A name=ss3-1548756><A href="http://service.gm.com/servlets/BlobShtml?ShtmlFile=1548756&amp;pubid=147#ss3-1548756" target="_blank">
<H5>Correction</A></H5>


Measure AC voltage and clean the wheel speed sensor mounting surfaces.

<LI ="1">Raise and support the vehicle. Refer to Lifting and Jacking the Vehicle in the General Information sub-section of the Service Manual (SI Document ID #899664).
<LI ="1">Disconnect both the front wheel speed sensor connectors at the frame and harness.
<LI ="1">Place a Digital Volt Meter (DVM) across the terminals of each wheel speed sensor connector.
<LI ="1">Rotate the wheel clockwise approximately one revolution per second. The minimum reading should be at least 350 ACmV's. If the reading is less than 350 ACmV's, remove the wheel speed sensor. Refer to the applicable Wheel Speed Sensor Replacement procedure in the ABS sub-section of the Service Manual.
<LI ="1">Plug the wheel speed sensor bore in order to prevent debris from falling into the hub during service.
<LI ="1">Clean the wheel speed sensor mounting surface using a wire brush, sand paper, emery cloth, scotch brite, or other suitable material. Be sure to thoroughly clean the wheel speed sensor surface. There should be no rust or corrosion.
<LI ="1">Check the sensor head to determine if it has been warped/distorted due to the corrosion build up or other causes. Check the mounting surface on the sensor head for flatness by placing it on the edge of a metal machinists scale or other suitable straight edge to measure the flatness. Check the sensor for flatness in multiple (minimum 3) positions/directions. If the sensor head is distorted, replace the sensor.
<LI ="1">Apply a thin layer of bearing grease to the hub surface and sensor O-ring prior to sensor installation. Use ONLY Wheel Bearing Lubricant, P/N 01051344 (Canadian P/N 993037).
<LI ="1">Install either the original sensor or a new one in the hub. Ensure that the sensor is seated flush against the hub. Refer to the applicable Wheel Speed Sensor Replacement procedure in the ABS sub-section of the Service Manual.
<LI ="1">Place the DVM across the sensor terminals and recheck the voltage while rotating the wheel. The voltage should now read at least 350 ACmV's. </LI><A name=ss4-1548756><A href="http://service.gm.com/servlets/BlobShtml?ShtmlFile=1548756&amp;pubid=147#ss4-1548756" target="_blank">
<H5>Parts Information</A></H5>
<TABLE width="100%" border=1><T>
<T>
<TR>
<TH vAlign=bottom align=middle>


Part Number</TH>
<TH vAlign=bottom align=middle>


Des

Just a fiddler at heart, took me 2 years to fix my ABS no fault codes all sensers had the correct readings. The valve body had a speck of dirt (probably from the brake fluid) that screwed every thing up.


good luck


what the heck happened here?????Edited by: letsgo