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Denso 234-5178 Air / Fuel Ratio Sensor - Upstream
| Brand | Denso 234-5178 |
|---|---|
| Position | Upstream |
| Connector Gender | Female |
| Grade Type | Regular |
| Sensor Type | Heated |
| Thread Diameter | 0.708 |
| Universal Or Specific Fit | Specific |
| Wire Quantity | 5 |
| Wiring Harness Length | 11.10 |
| Product line | OE Style |
| Fits | Subaru · 14 vehicles |
OE style replacement. Precision-built for exact replacement and a first-time fit.
Heated sensor. Helps deliver accurate air-fuel ratio monitoring.
Five-wire design with a female connector for straightforward installation.
Cross-references NTK 27004, Subaru 22641AA650 and Walker Products 250-25125 for the same application. See all 4.
Denso OE Style Air/Fuel Ratio Sensor
The Denso 234-5178 is a heated air/fuel ratio sensor built to OE-style specifications for direct replacement on select Subaru applications. It is engineered for exact fit and consistent signal performance, making it a practical choice for Subaru WRX and Subaru Forester upstream sensor replacement.
Denso’s OE Style line focuses on precision-built replacement parts that match original equipment fitment and connector design. For buyers searching for a direct-fit Subaru WRX upstream air/fuel ratio sensor or a Subaru Forester upstream oxygen sensor replacement, this part number 234-5178 is built for the application.
- Heated air/fuel ratio sensor for upstream placement
- Specific fit design for direct replacement installation
- 5-wire configuration with female connector
- Wiring harness length: 11.10
- Thread diameter: 0.708
- OE Style construction for exact replacement fit
Fitment Details
- Fits 2018-2021 Subaru WRX, Upstream; O.E. Quality Direct Fit Replacement Sensor; Air / Fuel Ratio Sensor - OE Style
- Fits 2018 Subaru Forester, Upstream; O.E. Quality Direct Fit Replacement Sensor; Air / Fuel Ratio Sensor - OE Style
- Fits 2014-2017 Subaru Forester, Upstream; OE Style
- Fits 2015-2017 Subaru WRX, Upstream; OE Style
What This Sensor Helps Address
- Check engine light related to upstream air/fuel ratio sensor faults
- Rough idle or unstable air-fuel readings
- Incorrect fuel trim readings from a failing sensor
- Emissions test failures caused by sensor response issues
- Driveability problems tied to inaccurate exhaust feedback
Installation Notes
Confirm upstream location, connector style, wire count, and thread diameter before installation. This sensor is a specific-fit replacement, so matching the vehicle year, model, and position is important for proper installation on Subaru WRX and Subaru Forester applications. Use the existing harness routing and verify the connector seats fully before clearing diagnostic codes.
Quality Assurance
Denso manufactures and tests OE Style sensors to strict original-equipment standards for fit and performance consistency. This part cross-references Subaru 22641AA650 and NTK 27004 for the same application.
| Year | Make | Model | Submodel | Position | Notes |
|---|---|---|---|---|---|
| 2021 | Subaru | WRX | — | Upstream | O.E. Quality Direct Fit Replacement Sensor; Air / Fuel Ratio Sensor - OE Style |
| 2020 | Subaru | WRX | — | Upstream | O.E. Quality Direct Fit Replacement Sensor; Air / Fuel Ratio Sensor - OE Style |
| 2019 | Subaru | WRX | — | Upstream | O.E. Quality Direct Fit Replacement Sensor; Air / Fuel Ratio Sensor - OE Style |
| 2018 | Subaru | Forester | — | Upstream | O.E. Quality Direct Fit Replacement Sensor; Air / Fuel Ratio Sensor - OE Style |
| 2018 | Subaru | WRX | — | Upstream | O.E. Quality Direct Fit Replacement Sensor; Air / Fuel Ratio Sensor - OE Style |
| 2017 | Subaru | Forester | 2.0XT Touring | Upstream | OE Style |
| 2017 | Subaru | Forester | 2.0XT Premium | Upstream | OE Style |
| 2017 | Subaru | Forester | 2.0XT Limited | Upstream | OE Style |
| 2017 | Subaru | WRX | — | Upstream | OE Style |
| 2016 | Subaru | Forester | — | Upstream | OE Style |
| 2016 | Subaru | WRX | — | Upstream | OE Style |
| 2015 | Subaru | Forester | — | Upstream | OE Style |
| 2015 | Subaru | WRX | — | Upstream | OE Style |
| 2014 | Subaru | Forester | — | Upstream | OE Style |
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