The study, which follows up on an initial evaluation from May 2008, noted "specific concerns" and areas where some comparison sites "need to go further".
These include obtaining better information from insurers about the excesses applied to their policies and the need to make the assumptions websites use in order to obtain quotes clearer to customers.
In addition, the FSA said that while adverts for most comparison sites were clear and not misleading, some "lack clarity" and could give customers a misleading expectation about their market coverage and the potential savings on offer.
FSA director of retail policy and conduct risk Dan Waters said: "We have contacted all websites involved in our review, to set out our findings and the standards we expect. Where needed, we are requiring firms to take prompt action to address our remaining concerns."
The 17 sites included in the FSA's review represent over 50 per cent of total sales volume for the sector.