ABS light stays on

The light being on means the system has detected a problem in one or more sensors. The vibration is the ABS modulating the brakes to prevent skidding because it has detected a wheel that is locked up. That wheel is most likely the one sensor that is giving you the error.

the ABS is anti brake skid which is designed to stop wheel lock up under brakes and allow steering control at all times
it was originally designed for aircraft to stop the under carriage from being ripped from the plane when the wheels (under brakes on landing ) hit a wet patch , snow or ice on the runway
it works by each wheel having a segmented sender that is read by a sensor and this impulse switches on valves in the electric pump in the hydraulic system so that when the wheel stops turning ,brake pressure to that wheel is released momentarily and then reapplied when the wheel turns again
the person using the brake still feels the same brake pressure under the foot and in extreme situations will feel the brake pedal pulsate
Now the ECM continually monitors the ABS system and when fluid sensors, or electronic sensors fall outside set parameters , the ABS light comes on to let you know that there is a problem with the brakes
you should now be having the fault codes read to find the reason for the light and have it repaired as in some systems ,if the repairs are not effected then the vehicle is put into limp mode by the ECM and that reduces the power available and the speed of the vehicle.

If you are referring to "anti-lock brakes", or "ABS", it means that when you depress the brake pedal hard enough, your computer recognizes the pressure and pulsates the brakes to prevent your wheels from locking up and the traditional skidding you see in movies.

ABS stops you quicker in emergency situations.

Few latest troubleshooting help links related to these problem.
ABS light stays on but brakes work fine? http://howtobyme.blogspot.com/2011/11/abs-light-stays-on-but-brakes-work-fine.html

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Sometimes ABS light comes on while Driving?

http://howtobyme.blogspot.com/2011/12/sometimes-abs-light-comes-on-while.html

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Brake Fade Issue? http://whoisbyme.blogspot.in/2012/07/brake-fade-issue.html Brake System Troubleshooting? http://technoanswers.blogspot.com/2011/11/brake-system-troubleshooting.html Car Brake lines have no pressure? http://schematicsdiagram.blogspot.com/2011/12/car-brake-lines-have-no-pressure.html Car Brakes Dragging? http://repairhelpcenter.blogspot.com/2011/12/car-brakes-dragging.html Car Brakes grabbing? http://repairhelpcenter.blogspot.com/2011/12/car-brakes-grabbing.html Car Brakes Making Noise? http://repairhelpcenter.blogspot.com/2011/12/car-brakes-making-noise.html Car Brakes Pulling? http://repairhelpcenter.blogspot.com/2011/12/car-brakes-pulling.html Pulsating Brake Pedal? http://repairhelpcenter.blogspot.com/2011/12/pulsating-brake-pedal.html Spongy brake pedal? http://repairhelpcenter.blogspot.com/2011/12/spongy-brake-pedal.html Hard Brake Pedal? http://repairhelpcenter.blogspot.com/2011/12/hard-brake-pedal.html Fading Sinking Brake pedal? http://whoisbyme.blogspot.in/2012/06/fading-sinking-brake-pedal.html Brakes make Grinding noise? http://repairhelpcenter.blogspot.in/2012/06/toyota-corolla-brakes-make-grinding.html

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These will help.
thanks.

Anti-Lock Braking System (ABS)
Purpose Anti-lock brake systems (ABS) - generally also referred to as anti-lock
systems (ALS) - are designed to prevent the vehicle wheels from locking
as a result of the service brake being applied with too much force, especially
on slippery road surfaces.
The idea is to maintain cornering forces on braked wheels to ensure that
the vehicle or vehicle combination retains its driving stability and manoeuvrability
as far as physically possible. The available power transmission
or grip between tyres and carriageway should also be utilised as
far as possible to minimise the braking distance and maximise vehicle
deceleration.
Why ABS? Although today commercial vehicle brakes are designed to a very high
technical standard, braking on slippery roads often results in potentially
dangerous situations. During full or even partial braking on a slippery
road it may no longer be possible to fully transfer the braking force onto
the road due to the low coefficient of friction (friction coefficient (k)) between
the tyres and the carriageway. The braking force is excessive and
the wheels lock up. Locked wheels no longer provide any grip on the
road and are almost incapable of transferring any cornering forces
(steering and tracking forces). This often has dangerous consequences:
- The vehicle becomes unsteerable
- The vehicle breaks away in spite of countersteering, and starts to
swerve.
- The braking distance is significantly increased
- Tractor-trailer combinations or semitrailer trains may break away or
jackknife.
Load sensing valve influence On dry roads today's load sensing valves (ALB) alone are often capable
of preventing the wheels from locking if the vehicle is unladen; they also
help the driver to effectively grade the braking process on wet road surfaces,
but they are unable to prevent locking as such (no slip monitoring).
In addition, they are unable to counteract any overreactions on the
part of the driver, or any variances in frictional or adhesion coefficients
which may apply to different sides of the vehicle, or indeed to its different
axles (?-split road surfaces).
Benefits of ABS: Only the Anti-Lock Brake System (ABS)
- guarantees stable braking characteristics on all road surfaces.
- maintains steerability and generally reduces the braking distance
- prevents vehicle combinations from jackknifing
- reduces tyre wear.
Limits of ABS Although ABS is an effective safety device, it can not suspend the limits
defined by driving physics. Even a vehicle fitted with ABS will become
uncontrollable if driven too fast around a corner.
So ABS is not a licence for a maladjusted style of driving or failure to observe
the correct safety distance.
4
ABS Training Anti-Slip Regulation (ASR)
Anti-Slip Regulation (ASR)
Why ASR? Increasing the engine output (accelerating) on a slippery road surface
can easily lead to the maximum adhesion on one or all powered wheels
being exceeded causing them to spin, especially if the vehicle is unladen
or partially laden.
Spinning wheels when driving off or accelerating represent a safety risk
just like locked wheel do when braking.
Reasons - Wheels that spin transfer just as little cornering force as locked
wheels.
- They also no longer transfer any tractive power onto the road.
Consequences - Vehicles that do not move or get stuck.
- Vehicles that can no longer be steered, jackknife on uphill uphill
gradients, or swerve in corners.
Benefits of ASR ASR prevents the powered wheel from spinning and provides the following
benefits:
- Tractive power and cornering forces are maintained.
- Stable driving behaviour is ensured when moving off, accelerating
and negotiating corners on slippery roads.
- The indicator lamp (if installed) is used to warn the driver of slippery
road conditions.
- Tyre wear is reduced to a minimum, and the motor vehicle's drive
train protected
- The risk of accidents is further reduced.
ASR and ABS: ASR represents a worthwhile addition to an ABS-controlled braking system.
All that is required to turn ABS control into full ABS/ASR control is
an ECU with the additional ASR function and a few additional components
for controlling the differential brake and the engine. This why ASR
is only available in combination with ABS.
Even a differential lock for off-road use and ASR do not exclude but complement
each other.
Limits of ASR The traction capacity of an all-wheel driven commercial vehicle can not
be achieved by a motor vehicle with only one driving axle - not even with
optimal ASR.

not really. Measn that you most likely have a wheel speed sensor bad. Most often its in the front of the truck and its replaced with the wheel bearing. Although the system is disabled while the light is on the vehicle brakes are not affected

the abs pump is losing pressure and kicks on when you apply the brakes at all to get up to the correct pressure.

One of the sensors has gone bad and needs to be replaced, the other thing to that would also do that is the ABS sensor is dirty or needs to be re gaped to the speed ring on the hub. There was a issue bulletin with your Tahoe on the ABS activating under 8 km/h. Good luck and hope this helps, if not clean out the sensor with brake parts cleaner and check the wire harness and ABS sensor bracket. Re gap the sensor to the speed ring hub. Here is the bulletin. Anti lock Brake (ABS) Activation at Low Speeds (Clean Wheel Speed Sensor Mounting Surface) #03-05-25-007C - (05/16/2006) 2001-2006 Chevrolet Suburban, Tahoe

First, is the ABS light on? Does it come on when it's doing it? Make sure the brake fluid is full, and the brakes are still servicable, ie, pads still have meat on them. If so, the abs control module or a speed sensor might be on the way out. This is a safety issue, and I would recommend getting the truck to a good mechanic to have it checked out.

I HAD ALMOST THE SAME PROBLEM .THIS CAR HAVE WAT SHOULD BE A RECALL WITH THE ABS SENSORS AT THE WHEEL .WHICH RUST BUIILDS ON THE SPINDLE AND THE BREAK THE SENSORS ..I END UP REPLACING THE BACK SENSORS AND THE SPINDLES .PLUS I WAITED SO LONG THAT THE ABS PUMP ALSO NEEDED REPLACEMENT ..GOT EXPENCIVE EVEN WITH DEALER EMPLOYEE DISCOUNT .I SPENT 1500 DOLLARS