Brake pedal sometimes sudders when pressed then the abs light comes on

id check your caliper to see if the piston is compressing all the way if not check your fluid it should be clean not brown or if you have been through large amounts of water if it has gotten into the brake system and check your bleeder valve to check if it has rotted or come lose or if you have a break in the lines or air, most likely your caliper is failing to compress.

You're going to meed to explain this better. Most brake lights don't have a switch. They come on automatically when you press your brakes.

check the calipers are not binding

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.

CAR IS NOT SAFE TO DRIVE.SOUND LIKE YOU HAVE PROBLEM IN THE HYDRALIC MODULATOR SOLENOIDS IN THE ABS HYDRALIC MODULATOR UNIT.THE DEALERSHIP NEED TO CHECK AND FIX.WHEN WORKING WITH ABS BRAKE SYSTEM YOU NEED DIAGNOSTIC EQUIPMENT TO FIX ABS BRAKES.

Check & replace if necessary the brake pedal switch placed above pedals on the support.
If the problem still occurs you might access the ABS ECU (Electronic Control Unit) using diagnostic equipment connected to the data link connector of the car, in order to pull out all DTC (Diagnostic Trouble Codes) memored.
Then you will be able to replace bad piece(s) and fix the problem by erasing all DTC stocked inside ABS ECU & reset it.

Brake light switch is not working. Electric brake controller is activating the shift lock. It's either the switch or the brake light fuse.

Add brake fluid and bleed the air out of the brake lines.

Its the abs sensor, if you encounter an ice patch or snow you won't even be able to stop because the pedal will will push back and make the rip grind noise. If you pull the ABS fuse out, you won't have ABS but you can stop and you won't have the grind noise and back pressure for now. Its safer to not have ABS when the sensor is faulty.

Simon Atari
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There is a switch mounted just above brake pedal, check that it is not sticking when you press pedal.