DTC will set when the following conditions are present:

WARNING: This page does not describe the selected car, but rather 7 other vehicles, including the 1997 GMC Savana Special, 1997 GMC Savana Camper Special, 1997 GMC Savana, 1997 Chevrolet RV Cutaway, and 1997 Chevrolet Cutaway. However, it is still accessible from the selected car via links, so may be relevant.

No TP sensor DTCs are set.
No EVAP DTCs are set.
No IAT sensor DTCs are set.
No MAP sensor DTCs are set.
No ECT sensor DTCs are set.
No MAF sensor DTCs are set.
No intrusive test is in progress.
No device controls are active.
System voltage is at least 9 volts.
HO2S transition time from lean to rich or rich to lean is greater than 100 milliseconds.