WARNING: This page is about a different car, the 2003 Oldsmobile Aurora. However, it is still accessible from the selected car via links, so may be relevant.
Fig 1: DTC P0418: Secondary Air Injection Pump Relay Control Circuit (Steps 1-9)
Courtesy of GENERAL MOTORS CORP.
Fig 2: DTC P0418: Secondary Air Injection Pump Relay Control Circuit (Steps 10-19)