I have a 98 Jetta 2.0L showing a trouble code of 411. The translation of the code is the following:

DTC 411: Secondary Air Injection
1) Circuit Relay defective or fuse open
2) Check Connector and wiring
3) Air pump defective or hoses blocked
4) Refer to A2 commercial preferred customer

(Whatever number 4 means)?

My question is this: What is a secondary air injection and where is it located on this car? I restore antique cars but have limited experience with newer technology cars. As soon as I figure out what to do I am confident I can do it, but where to start is the question. Pictures showing what a secondary air injection is would be most helpful too, but if you can tell me where to look, that would be appreciated too.