Code 21 on prelude ECU

[hontegra]

hi guys,
thanks for your help on the last post but now i have another problem. My h22 runs fine except it will not kick into vtec my ecu has thrown a code 21 which i know to be vtec solenoid valve. do any of you know the testing procedure for that part? also could air in my cooling system be the cause of the code? (i know hondas are tempermental about air in the cooling system). any suggestions or ideas.
thanks

[hontegra]

Well i haven't had a chance to take apart the solenoid to see if the filters are clogged yet but as for the wiring. i checked the wire and it seems intact. As far as wiring are there any other systems that could have an effect on a code 21 ?