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Spec sheet at a glance

Check these numbers before you blame the harness or the ECU. Heater readings outside these windows mean the sensor is done.

Why planar beats thimble here

Faster light-off, cleaner cold starts

Planar zirconia elements reach their 700°C internal operating temperature in under 10 seconds. Thimble designs need 25+ seconds. Less open-loop dwell improves cold-start emissions compliance by an estimated 12–18%, per FAE and Ceradex 2026 manufacturing white papers.

The flat ceramic substrate carries a screen-printed platinum electrode array. Output swings between 0.1V lean and 0.9V rich, crossing over above 3 Hz at temperature. Upstream, that signal is the ECU's primary fuel trim feedback. Downstream, it gives the ECU a post-catalyst oxygen comparison for catalyst health monitoring.

Materials that survive a 24-year-old exhaust

Hex bodies are high-temperature AISI 316 stainless steel with nickel-plated brass terminal inserts to block galvanic corrosion at the bung. Connector shells are a reinforced high-temp composite rated to 160°C continuous and 200°C peak — against a measured 140°C–175°C at the upstream bung under wide-open throttle on the EJ251.

The element is yttria-stabilized zirconia with a platinum-coated alumina electrode matrix, resistant to silicone and oil fouling. Heater circuits hold SAE J1343 tolerance with ±10% drift allowed over service life. Manufacturing runs under ISO 9001:2026 traceability.

A matched pair switches identically — so cross-sensor variance is off your suspect list when you're chasing P0420 or fuel trim codes.

DTC codes this kit addresses

• P0030–P0039 — HO2S heater circuit range, including the common P0031 and P0037 heater faults.
• P0130–P0147 — O2 sensor circuit faults on Bank 1 Sensors 1 and 2, covering the P0130–P0136 voltage range.
• P0171 / P0172 — system too lean / too rich, often secondary to a degraded AFR feedback loop.
• P0420 — catalyst efficiency below threshold (Bank 1), frequently triggered by lazy sensor feedback.
• P1130–P1143 — Subaru OEM-specific AFR sensor range codes.
• P0150–P0167 — Bank 2 equivalents, applicable to H6 platforms.

Any 2026-era scan tool talks to these sensors: Subaru SSM-IV, Ford IDS, GM GDS2, Toyota Techstream, Snap-on ZEUS+, Autel MaxiSYS Ultra. CAN 3.0 extended addressing lets you watch Mode $06 TID $01–$0A for switching frequency, rich-to-lean transition time, and heater current draw trends.

Fitment: which Subarus take this kit

Direct fit is the 2000–2002 Impreza with EJ251 (2.5L NA), EJ253, or EJ20 (2.0L H4). Cross-fit per the compatibility matrix: 1999–2002 Forester (SF), 2000–2004 Legacy/Outback (BE/BH), and select 2002–2005 Impreza WRX (EJ205) downstream positions.

Verify connector keying before you order. Subaru sourced sensors from both Denso and Bosch in this era, and shell geometry differs. This kit carries the Denso-pattern connector dominant on naturally aspirated 2000–2002 Impreza models.

Newer Impreza or Forester? Different part

The 2006–2012 generation uses a separate downstream assembly. Match it with the 22690AA810 downstream oxygen sensor for 2006–2012 Subaru Impreza and Forester.

ABS warnings on the same chassis

At this age, wheel speed sensors fail too. The 2pcs ABS wheel speed sensor set for Impreza, Forester, and WRX covers the front right and left positions.

Electrical suspects behind trim codes

Charging and ECU faults can mimic a lazy sensor. If both O2 sensors test clean electrically, work through the starters, alternators, and ECU collection next.

Wheels while you're wrenching

Refreshing a 5x100 Impreza, Forester, or Outback? The 1-inch wheel spacer guide for 5x100 Subarus covers 12x1.25 stud fitment.

FAQ: diagnosis, fitment, and service life