09款圣达菲后左氧传感器39210-3E140，排气管下游检测。

If your 2009 Santa Fe shows engine check light, high fuel consumption, or weak acceleration, likely the rear-left oxygen sensor (downstream of the catalytic converter) aged or failed. It monitors oxygen content after the catalyst and feeds ECU to precisely control air-fuel ratio; compatible with 2009 Hyundai Santa Fe; OEM 39210-3E140. Installation should be done cold; remove old sensor; clean threaded hole of carbon buildup; apply anti-seize; torque to standard. Tighten to prevent leaks.