Preliminary Checks
WARNING: This page is about a different car, the 2003 Pontiac Vibe. However, it is still accessible from the selected car via links, so may be relevant.
See PRELIMINARY CHECKS under SYMPTOMS - ENGINE CONTROLS.
The fault must be present to be diagnosed correctly with a DTC procedure. If the fault that set the DTC is intermittent, then the use of DTC procedures may result in replacement of good parts.