There is a switch just behind the brake pedal up under the dash. This switch
disengages the cruise control when you press on the brake pedal. This switch is
adjustable for distant between the switch and brake pedal. Check it and see if
has come unlocked and when you hit a bump on the highway ( we all know how
smooth our highway are) that it is hitting the arm of the brake pedal. It
doesn't take much of a bump or push on this switch to turn off the cruise
control.
Good Luck
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