Oxygen Sensors for Toyota 4Runner (2003-2004) 4.0L Upstream & Downstream

Direct-Fit Oxygen Sensor Set for 2003-2004 Toyota 4Runner (N210)

What it Does: The complete 4-piece oxygen sensor kit monitors exhaust gas chemistry on the 2003-2004 Toyota 4Runner to restore precise closed-loop fuel trim mapping and eliminate catalyst efficiency diagnostic trouble codes.

The Stock Toyota 4Runner Sensor Degradation

Factory air-fuel ratio and zirconia oxygen sensors on the fourth-generation N210 platform suffer from internal ceramic element contamination and thermal fatigue after thousands of heat cycles. As silicone deposits, carbon soot, and fuel additives coat the sensing thimble, response latency increases. On the 1GR-FE 4.0L V6, this sluggish sensor transition forces the engine control module into erratic short-term fuel trims, leading to sub-optimal stoichiometry, rich-condition spark plug fouling, decreased fuel economy, and diagnostic trouble codes such as P0130, P0161, P0420, and P0430.

The Engineering Solution

This replacement set delivers four matched, pre-calibrated sensors engineered to restore factory signal integrity across both exhaust banks. Featuring platinum-electroplated ceramic planar elements inside double-laser-welded stainless steel protective sheaths, these sensors resist thermal shock and exhaust particulate poisoning. Pre-applied high-temperature anti-seize compound prevents thread galling in the factory cast-iron bungs. Factory-spec wiring harnesses, heat-resistant fiberglass sleeving, and OE-keyed 4-pin weather-pack connectors ensure exact plug-and-play installation without wire splicing or circuit resistance variation.

What's Included

• 2x Upstream Oxygen / Air-Fuel Ratio Sensors
• 2x Downstream Oxygen Sensors

Technical Specifications

Compatibility

• 2003 Toyota 4Runner 4.0L V6 (SR5, Limited, Sport Edition)
• 2004 Toyota 4Runner 4.0L V6 (SR5, Limited, Sport Edition)

Frequently Asked Questions & Fitment Warnings

Does this fit the N210 4Runner?

Yes, this is a direct fit for the 2003-2004 Toyota 4Runner equipped with the 1GR-FE 4.0L V6 engine. This set is not compatible with models equipped with the 4.7L 2UZ-FE V8 engine.

Do I need special tools to complete the installation?

A slotted 7/8-inch (22mm) oxygen sensor socket or offset flare wrench is recommended to clear the harness while breaking the factory sensors loose from exhaust bungs.

The Toyota Durability Standard

Restoring closed-loop fuel management on the N210 4Runner maintains continuous combustion efficiency, protecting your catalytic converters and preserving the robust off-road crawling and towing reliability built into the 4.0L platform.