Thread: The dreaded fault code 21, Vtec spool valve.

This fault throws on the engine light randomly between the revs of 5000-7000rpm in my d16y8, sometimes not at all when the car is semi cold.

Any idea what tends to go wrong with these? Short or open circuit in solenoid, sticky valve?

Any helps much appreciated.

I'm not sure if the d16y8 is a vtec-e motor or just typical vtec, as it seems the motor rev's out fine without loss of power, yet it hesitates at lower rpm..... So vtec may still be engaging, so could be just higher enough resistance to fault at higher rpm. It's a little weird how it doesn't seem to throw the light at a set rpm.