P0171 and P0174 indicate your Infinity is running lean in both Bank 1 and Bank 2. Bank 1 and 2 refer to the engine's number one cylinder side and the opposing side. Running "lean" means either not enough fuel is getting to the combustion chambers, or too much air is being mixed in with the fuel.
First you'll need to look into things which would cause unmetered air to enter the intake manifold, such as cracked or disconnected vacuum hoses.
Second you should inspect things which would cause inadequate fuel delivery such as emission sensors which may be reporting false values to the ECU (engine control computer). A good example of an emission component would be a defective MAF (Mass Air Flow Sensor). A good example of a mechanical component would be a dirty fuel filter or weak fuel pump.
posted by SmogTips Support 11-16-2011 05:10 PM