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 P2135: TP Sensor Signals 1 & 2 Disagree Or Outside Predetermined Range (Steps 1-11)
Courtesy of GENERAL MOTORS CORP.
Fig 2: DTC P2135: TP Sensor Signals 1 & 2 Disagree Or Outside Predetermined Range (Steps 12-21)