Help wanted :) CODE P0128

[RyanAhn]

hey guys,

I got a service engine soon light few days ago.
but the first time I got a jammed VANOS solenoid and fixed it.
The day after I fixed VANOS problem, I got that warning light again.
The code was P0128, but the coolant temp level looks good for me(headed straight 12hr direction, car runs fine, heater works fine).

DO I need to go a shop and fix it?
I know that I need to get it fixed sometime in the future.
but is it kind of a serious thing? or I can just clear the warning code and wait?

thx for reading!

cheers!