i suggest doing a search on the subject on the forum, since causes and solutions are discussed constantly. you'll find days of reading on the subject. TriGuy and f1100turbo just about covered it.
also, welcome and you may want to start posting in the Expandable/Hybrid section here at FRF. there's a Roo sub-section there.
be sure to post your year and model of Roo.
lots of help with hybrid-specific issues there.
and Zoe the Wonder Dog(R.I.P.)
'07 Roo 23SS pushing an '07 Chevy Avalanche
Equalizer WDH and Prodigy BC