{"product_id":"oxygen-sensors-for-subaru-impreza-1999-2004-2-5l-downstream","title":"Oxygen Sensors for Subaru Impreza (1999-2004) 2.5L Downstream","description":"\u003ch2\u003eDirect-Fit Downstream Oxygen Sensor for 1999-2004 Subaru Impreza\u003c\/h2\u003e\n\n\u003cp\u003e\u003cstrong\u003eWhat it Does:\u003c\/strong\u003e The Downstream Oxygen Sensor monitors post-catalytic exhaust stream chemistry on the 1999-2004 Subaru Impreza to ensure proper catalyst efficiency, maintain closed-loop trim balance, and eliminate false emissions trouble codes.\u003c\/p\u003e\n\n\u003ch3\u003eThe Stock Subaru Impreza Sensor Fouling and Thermal Degradation\u003c\/h3\u003e\n\u003cp\u003eFactory oxygen sensors on the \u003cstrong\u003eEJ251\u003c\/strong\u003e naturally aspirated boxer platform endure brutal thermal cycling due to their proximity to the catalytic converter under the transmission tunnel. Over time, original zirconia sensing elements suffer from soot accumulation, silicone poisoning, and thermal fatigue. This degradation leads to sluggish response rates and incorrect downstream voltage signals, frequently triggering intermittent P0420 catalytic efficiency diagnostic trouble codes and degraded closed-loop secondary fuel corrections.\u003c\/p\u003e\n\n\u003ch3\u003eThe Engineering Solution\u003c\/h3\u003e\n\u003cp\u003eThis replacement downstream sensor utilizes a fast-reacting planar ceramic sensing cell enclosed in a high-grade 304 stainless steel housing. Engineered with an integrated high-efficiency heating circuit, it reaches optimal light-off operating temperatures rapidly to prevent cold-start enrichment errors. Precision-machined M18x1.5 threads ensure gall-free installation into the exhaust bung, while a heavy-duty submersible harness with an OEM-spec weather-pack connector resists heat exposure and moisture intrusion under aggressive chassis vibration.\u003c\/p\u003e\n\n\u003ch3\u003eTechnical Specifications\u003c\/h3\u003e\n\u003ctable width=\"100%\" style=\"border-collapse: collapse; border: 1px solid #e0e0e0; font-size: 14px; margin-bottom: 20px;\"\u003e\n  \u003ctr style=\"background-color: #f9f9f9;\"\u003e\n\u003cth style=\"padding:10px; text-align: left; border: 1px solid #e0e0e0;\"\u003eFitment\u003c\/th\u003e\n\u003ctd style=\"padding:10px; border: 1px solid #e0e0e0;\"\u003e1999-2004 Subaru Impreza\u003c\/td\u003e\n\u003c\/tr\u003e\n  \u003ctr\u003e\n\u003cth style=\"padding:10px; text-align: left; border: 1px solid #e0e0e0;\"\u003eEngine \/ Chassis\u003c\/th\u003e\n\u003ctd style=\"padding:10px; border: 1px solid #e0e0e0;\"\u003e\n\u003cstrong\u003eEJ251\u003c\/strong\u003e \/ \u003cstrong\u003eGC6\u003c\/strong\u003e, \u003cstrong\u003eGD6\u003c\/strong\u003e, \u003cstrong\u003eGG6\u003c\/strong\u003e\n\u003c\/td\u003e\n\u003c\/tr\u003e\n  \u003ctr style=\"background-color: #f9f9f9;\"\u003e\n\u003cth style=\"padding:10px; text-align: left; border: 1px solid #e0e0e0;\"\u003eStock Output\u003c\/th\u003e\n\u003ctd style=\"padding:10px; border: 1px solid #e0e0e0;\"\u003e165 hp \/ 166 lb-ft\u003c\/td\u003e\n\u003c\/tr\u003e\n  \u003ctr\u003e\n\u003cth style=\"padding:10px; text-align: left; border: 1px solid #e0e0e0;\"\u003eReplaces OEM Part #\u003c\/th\u003e\n\u003ctd style=\"padding:10px; border: 1px solid #e0e0e0;\"\u003eN\/A\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003c\/table\u003e\n\n\u003ch3\u003eCompatibility\u003c\/h3\u003e\n\u003cul\u003e\n  \u003cli\u003e1999-2001 Subaru Impreza 2.5RS Coupe\/Sedan (\u003cstrong\u003eGC6\u003c\/strong\u003e) 2.5L H4\u003c\/li\u003e\n  \u003cli\u003e2002-2004 Subaru Impreza 2.5RS Sedan (\u003cstrong\u003eGD6\u003c\/strong\u003e) 2.5L H4\u003c\/li\u003e\n  \u003cli\u003e2002-2004 Subaru Impreza 2.5TS Sport Wagon (\u003cstrong\u003eGG6\u003c\/strong\u003e) 2.5L H4\u003c\/li\u003e\n  \u003cli\u003e2002-2004 Subaru Impreza Outback Sport Wagon (\u003cstrong\u003eGG6\u003c\/strong\u003e) 2.5L H4\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003ch3\u003eFrequently Asked Questions\u003c\/h3\u003e\n\u003cp\u003e\u003cstrong\u003eDoes this fit the GC and GD Impreza?\u003c\/strong\u003e\u003cbr\u003e Yes, this is a direct fit for the 1999-2004 Subaru Impreza equipped with the 2.5L \u003cstrong\u003eEJ251\u003c\/strong\u003e engine in the downstream position.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eWill this sensor clear a persistent P0420 Check Engine Light?\u003c\/strong\u003e\u003cbr\u003e If your P0420 code is triggered by a biased, slow-responding downstream sensor rather than an exhaust leak or failed converter core, this direct replacement will restore proper diagnostic voltage switching.\u003c\/p\u003e\n\n\u003ch3\u003eThe Subaru Performance Caliber\u003c\/h3\u003e\n\u003cp\u003eProper sensor feedback is critical to maintaining crisp boxer engine throttle response and stable fuel trims. Built to survive rally stages and daily commuting alike, this sensor restores OEM diagnostic accuracy without compromise.\u003c\/p\u003e","brand":"VelocityMax","offers":[{"title":"Default Title","offer_id":50511714320632,"sku":"DS-EYFCD6J44","price":69.95,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0800\/1290\/2648\/files\/oxygen-sensors-for-subaru-impreza-1999-2004-2-5l-downstream-1.jpg?v=1789418230","url":"https:\/\/performancechiptuning.com\/products\/oxygen-sensors-for-subaru-impreza-1999-2004-2-5l-downstream","provider":"Performance Chip Tuning","version":"1.0","type":"link"}