During the commanded purge phase, the ECU detects insufficient flow from the charcoal canister to the intake manifold. The purge solenoid valve or the canister itself is not allowing adequate flow.
Common causes
Stuck-closed purge solenoid valve (most common)
Blocked or kinked purge hose
Saturated or blocked charcoal canister
Vacuum port blocked at intake manifold
Symptoms
MIL illuminated
Rough idle or hesitation when purge activates
Fuel odor
Rich fuel trims during cruise
EVAP monitor fails
Severity
Moderate — causes idle irregularities and mixture enrichment; prolonged fault can further saturate the canister.
What to do
Command purge solenoid open and closed with scan tool and check for flow or vacuum