Solved: OBD2 Error Codes 0171 and 0174 on 2000 Ford Taurus - Vacuum Leak Fix

I recently resolved a persistent check engine light issue on my 2000 Ford Taurus after discovering error codes 0171 and 0174. Initially, the system only displayed code 0174, followed by 0171 appearing later. My local auto parts store suggested replacing the oxygen (O2) sensors—commonly recommended for this issue—but after installing new sensors with no improvement, I realized the root cause was elsewhere. After researching extensively on this forum, I identified two significant vacuum leaks: one at the rear of the intake manifold where a hose had disconnected, and another in the rubber PCV valve tube that was completely rotted. Once both leaks were repaired, I disconnected the negative battery cable to reset the engine control module. Since then, I've driven over 300 miles without any check engine light activation. My vehicle also passed its recent emissions inspection successfully. This experience highlights how vacuum system issues often underlie OBD2 codes like 0171 and 0175 on older Ford Taurus models—especially in vehicles from the early 2000s with aging intake components.