99 silverado z71. i have both of these codes which are..
C0237 Speed sensor erratic, rear
C0238 Stop lamp switch circuit

abs light comes on at different times....normally above 30 or so...but really all over the place. sometimes just flashes on then off...others, comes on and stays for longer... bumps seem to trigger as well as hitting brakes.....

i have noticed the red brake light flash on before as well......

any ideas?