Unfortunately you really need to check both under the hood and under the vehicle for sign(s) of PS fluid leak(s).
You need to idle first (like 5mins), check the PS hoses and PS Lines.
In my case PS suction hose and PS line to radiator was the culprit.
I also replaced the PS reservoir (as a preventive maintenance)
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Edit: TEMP FIX until the warm weather hits
OR you can just top off the PS fluid (ATF or CHF 11s) - check you vehicle PS reservoir label.
(turn the wheel max left and max right - this activates the PS pump to circulate the fluid), check the level again.