O2 Oxygen Sensor Upstream Downstream for Toyota 4Runner (1996-2000) 3.4L

Direct-Fit Upstream & Downstream Oxygen Sensor Kit for 1996-2000 Toyota 4Runner (N180)

What it Does: This matched upstream and downstream oxygen sensor kit monitors exhaust air-fuel ratios and catalytic converter efficiency on the 1996-2000 Toyota 4Runner (N180) powered by the 5VZ-FE 3.4L V6 engine to maintain closed-loop fuel trim precision.

The Stock Toyota 4Runner Sensor Failure

Factory oxygen sensors on the N180 chassis equipped with the 5VZ-FE 3.4L V6 endure relentless thermal cycling, moisture intrusion, and carbon fouling over high mileage. Over time, the internal zirconia sensing element degrades and the integrated heater circuit fractures, delaying closed-loop ECU operation during cold starts. Sluggish voltage switching forces the ECM into rich fuel trims, triggering P0135, P0141, or P0171 fault codes while risking catalytic converter overheating.

Common Symptoms of a Failing OEM Oxygen Sensor

• Check Engine Light / DTCs: Illuminated MIL with P0135 (upstream heater circuit), P0141 (downstream heater circuit), or P0420 catalyst efficiency faults.
• Rough Idle & Hesitation: Delayed voltage feedback disrupts fuel trims, causing surging or sluggish throttle response under load.
• Poor Fuel Economy: Rich open-loop operation drops MPG significantly, fouls spark plugs, and causes failed emissions testing.

The Direct-Fit Zirconia Oxygen Sensor Solution

This matched upstream and downstream sensor pair replaces worn factory units with OEM-grade zirconia ceramic sensing elements engineered for rapid light-off and accurate millivolt response. Laser-welded stainless steel housings shield the internal electrodes against exhaust condensation and thermal shock under heavy load. Pre-terminated factory-style connectors and OEM-spec wiring harnesses match the E83185400CP specification for plug-and-play installation without splicing. Replacing both positions simultaneously restores balanced closed-loop feedback for the 5VZ-FE 3.4L V6.

What's Included

• 1 Upstream Oxygen Sensor (Direct-Fit)
• 1 Downstream Oxygen Sensor (Direct-Fit)

Technical Specifications

Compatibility

• 1996-2000 Toyota 4Runner 3.4L (Upstream & Downstream Positions)

Frequently Asked Questions & Fitment Warnings

Does this fit the N180 4Runner?

Yes. This is a direct fit for the 1996-2000 Toyota 4Runner equipped with the 5VZ-FE 3.4L V6 engine. Excludes 2.7L 3RZ-FE 4-cylinder models; confirm your engine displacement and emissions specification before ordering.

Will replacing both sensors clear P0135, P0141, or P0420 codes?

Yes, for sensor-related faults. Replacing failed sensors eliminates heater circuit codes like P0135 and P0141, though a persistent P0420 code after installation indicates a degraded catalytic converter.

Is any wiring modification required for installation?

No. Both units include OEM-style connectors matching E83185400CP for plug-and-play installation; torque cleanly to factory specification without contaminating the sensor tip.

The Toyota Heavy-Duty Standard

Engineered for high exhaust gas temperatures under towing loads and off-road climbs, this matched oxygen sensor set restores factory air-fuel metering on the N180 platform. Dependable closed-loop feedback keeps your 5VZ-FE 3.4L V6 running clean, efficient, and ready for high-mileage duty.