O2 Oxygen Sensor Upstream for Infiniti Vehicles (2002-2006)Precision Upstream A F Monitoring for the VK45DE and VQ35DE Platforms Who Its For: Engineered for Infiniti owners running the VK45DE V8 or VQ35DE V6 powerplants who are experiencing erratic idling, poor fuel economy, or a stubborn check engine light. The Symptom: The factory upstream sensors on these Infiniti platforms are the primary eyes of the ECU, responsible for monitoring the air fuel ratio before the exhaust hits the catalytic converters. Over