DTC will test when the following conditions are present:

WARNING: This page is about a different car, the 1997 GMC Pickup and 1997 Chevrolet Pickup. 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.
Engine run time is greater than 2 minutes.