Smog Pump: What is it and how to replace

My 2000 Venture just threw the code for the smog pump. What is it and how much am I looking at to replace? In addtion, since it probably will involve lifting the engine should I go ahead and replace anything else as a preventive maintenance thing?

How many miles have you put on it? What have you done to it?

Smog pump IIRC is an electric air pump that injects air into the exhaust to make the catalytic reaction more efficient, the pump could be bad, or one of the check valve(s) could be bad?