ETS Light 1999 Cavalier

What sets the ETS light. And is there a code reader or something to tell why the light is on?

Loss of an input from a wheel speed sensor or brake blocking solenoid can set the warning system. A bi-directional scanner with ABS capability can retrieve the codes and data, and run functional tests of the system to help determine the cause.

The typical PCM scanner alone will be of little use for this.