I have a 2001 Gmc Duramax 3500 dually! Occasionaly on dry surface while brakeing and slowing, almost stopped! The Brake pedal will jump and pump against my foot and I hear a noise up front! The only thing I can think of its something with anti lock feature! It happened quite often this summer on dry roads! Any ideas about this! Have you had to fix this problem. Is it a computer upgrade in some module. I would like to fix it before heading south this winter! All ideas are sure welcomed! Thanks, Dan in cold Minnesota !!!!

You might want to have the hydroboost system checked out, wondering if it's a pressure fluctuation. Do you notice anything funny with the steering when this happens, hydroboost powers both systems.

I suspect it is an ABS sensor problem, probably one in the front. My '94 'burb does that sometimes. Do you have access to a scanner? The scanner will show wheel speed of each wheel. If it is a sensor, it will show an erratic reading on that wheel.

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

</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 href="http://service.gm.com/servlets/BlobShtml?ShtmlFile=1548756&psdid=210&evc=sm#ss1-1548756">Condition

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 href="http://service.gm.com/servlets/BlobShtml?ShtmlFile=1548756&psdid=210&evc=sm#ss2-1548756">Cause

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 href="http://service.gm.com/servlets/BlobShtml?ShtmlFile=1548756&psdid=210&evc=sm#ss3-1548756">Correction

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

<LI type=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 type=1>Disconnect both the front wheel speed sensor connectors at the frame and harness. <LI type=1>Place a Digital Volt Meter (DVM) across the terminals of each wheel speed sensor connector. <LI type=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 type=1>Plug the wheel speed sensor bore in order to prevent debris from falling into the hub during service. <LI type=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 type=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 type=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 type=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.
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.
<A href="http://service.gm.com/servlets/BlobShtml?ShtmlFile=1548756&psdid=210&evc=sm#ss4-1548756">Parts Information

<TABLE width="100%" border=1><TBODY><TR><TH vAlign=bottom align=middle>Part Number

</TH><TH vAlign=bottom align=middle>Description

</TH></TR><TR><TD vAlign=center align=middle>01051344

(Canadian P/N 993037)

</TD><TD vAlign=center align=middle>Wheel Bearing Lubrication - Tub

</TD></TR></TBODY></TABLE>

Parts are currently available from GMSPO.

Does anybody know if you have to remove the front hub assembly to get at the sensor? My trucks abs has been coming on when it shouldnt so I measured the ac voltage at each sensor like described above and the left was 280mv and the right was 210mv. I also was wondering if you should just put new sensors in once you get that far. If anyones already done this I would appreciate any tips. Thanks