DTC P1521: VRIS Solenoid Valve No. 1 Circuit Malfunction: Condition

WARNING: This page is about a different car, the 2002 Mazda 626. However, it is still accessible from the selected car via links, so may be relevant.

DTC P1521 is set when Variable Resonance Induction System (VRIS) solenoid valve No. 1 control signal malfunctions. This is a continuous monitor. Possible causes are:

VRIS solenoid valve No. 1 malfunction.
Short circuit between VRIS solenoid No. 1 and PCM.
Open circuit between VRIS solenoid No. 1 and main relay.
PCM malfunction.