2002 Cadillac Escalade 02 Stability Service Light Came Took Get Checked Out

I have a 02 escalade and the stability service light came up. I took it to get checked out and the mechanic said tha the code was P1518 Throttle Actuator Control (TAC) Module Serial Data Circuit. They said it as about $700 to fix this but they are not sure if this will solve the problem