My wifes car failed the smag test with a OBD Fault code of P0171 and P0174.

unfortunately there is not enough information to diagnose the cause or give an estimate. P0171 & P0174 are Bank 1, Bank 2 system lean codes. What that means is that the engine is getting to much air or too little fuel or that the MAF sensor is misreading the amount of air coming in so the engine computer does not calculate the injector time for the actual airflow. The V6 engine had some common problems with the PCV hose near the rear of the intake manifold and intake vacuum leaks that caused a lean condition and the related codes. You can visually check the PVC hose or have a mechanic check the hose and also check for vacuum leaks. The MAF can be cleaned. It is best to have a scanner hooked to read fuel trim, O2 and MAF information while testing to diagnose it. If the PCV hose is deteriorated, replace it. You'll need to have it checked by a mechanic to clear the codes and check the system operation and Monitor Status before taking it back to Smog. I hope this helps and good luck! Robert Grove www.wego2umobilemechanic.com www.orangecountymobileautorepair.com