Oxygen Sensors for Scion xA xB (2004-2006) 1.5L Upstream & Downstream

Direct-Fit Oxygen Sensor Kit for 2004-2006 Scion xA, xB

What it Does: The Oxygen Sensor Kit replaces degraded upstream and downstream lambda sensors on the 2004-2006 Scion xA and xB to restore proper air-fuel closed-loop feedback, correct fuel trims, and eliminate catalyst efficiency trouble codes.

The Stock Scion xA, xB Sensor Degradation

With age and thermal cycling, the factory zirconium dioxide sensing elements in the NCP31 and NCP61 exhaust tracts suffer from chemical poisoning, silicone contamination, and soot coating. Over 100,000 miles, this degradation dampens sensor voltage switching response times between rich (0.9V) and lean (0.1V). The factory 1NZ-FE ECU responds by defaulting to rich safe-mode fuel mapping, causing poor combustion efficiency, unburned hydrocarbon buildup, rough idle, failing emissions inspections, and recurring diagnostic trouble codes such as P0135, P0141, or P0420.

The Engineering Solution

This 2-piece replacement kit features precision planar sensing elements housed within dual-layer protective 304 stainless steel heat shielding. The internal ceramic electrolyte provides high thermal shock resistance and rapid heater circuit activation to achieve operating temperature (600°F) in seconds. Integrated high-temperature PTFE-insulated wiring harnesses, silicone rubber outer weather seals, and OE-pinned direct-fit locking connectors eliminate the signal resistance and failure points common with universal wire-splicing repairs. Calibrated resistance values deliver precise millivolt feedback to restore factory stoichiometric AFR targets.

Technical Specifications

Compatibility

• 2004-2006 Scion xA Base Hatchback 5-Door 1.5L L4 (1NZ-FE / NCP61)
• 2004-2006 Scion xB Base Wagon 5-Door 1.5L L4 (1NZ-FE / NCP31)

Frequently Asked Questions

Does this fit the NCP31 and NCP61 xA, xB?
Yes, this is a direct fit for the 2004-2006 Scion xA and xB equipped with the 1.5L 1NZ-FE engine.

Do I need to calibrate or tune the ECU after installing these sensors?
No tuning is required; clear existing OBD-II diagnostic fault codes and let the ECU complete a drive cycle to relearn fuel trims.

The Scion JDM Reliability Standard

Engineered to withstand continuous vibration and thermal cycling, this oxygen sensor set restores peak fuel economy, crisp throttle response, and pristine emissions compliance to your high-revving 1NZ-FE powertrain.