WARNING: This page is about a different car, the 2003 GMC Envoy XL and 2003 Chevrolet TrailBlazer. However, it is still accessible from the selected car via links, so may be relevant.
Fig 1: DTC P1518: TAC Module Serial Data Fault (Steps 1-8)
Courtesy of GENERAL MOTORS CORP.
Fig 2: DTC P1518: TAC Module Serial Data Fault (Steps 9-16)
Courtesy of GENERAL MOTORS CORP.
Fig 3: DTC P1518: TAC Module Serial Data Fault (Steps 17-24)
Courtesy of GENERAL MOTORS CORP.
Fig 4: DTC P1518: TAC Module Serial Data Fault (Steps 25-29)