DTC Will Set When The Following Conditions Are Present:

WARNING: This page is about a different car, the 1997 GMC Savana, 1997 Chevrolet Chevy Van, and 1997 Chevrolet Chevy Express. 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.