DTC will set 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.

Engine is running.
No TP sensor DTCs are set.
No MAP sensor DTCs are set.
No EVAP DTCs are set.
EGR DTC P0401 is not set.
MAF DTCs P0102 or P0103 is not set.
System voltage is greater than 11 volts but less than 16 volts.
Canister purge duty cycle is less than 99.6 percent.
Change in throttle position is less than 3.9 percent.
EGR duty cycle is less than 89.9 percent.
EGR pintle position is less than 89.9 percent.
Engine vacuum is less than 90 kPa.
Throttle position is less than 89.8 percent.
Listed conditions are met for greater than 2 seconds.
Change in MAF sensor is greater than a calculated value.