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NTK 25661 Oxygen Sensor - Downstream
| Brand | NTK 25661 |
|---|---|
| Position | Downstream |
| Wiring Harness Length | 74.7500 |
| Sensor Type | Heated |
| Universal Or Specific Fit | Specific |
| Wire Quantity | 4 |
| Thread Diameter | 18.000 |
| Mounting Type | Threaded |
| Product line | Direct Fit Oxygen Sensor |
| Fits | Audi · 10 vehicles |
Direct fit design. Specific application coverage for OE-style replacement and consistent sensor matching.
Heated sensor. Helps the sensor reach operating temperature quickly for responsive exhaust feedback.
OE-tested quality. Manufactured and tested to meet or exceed original equipment specifications.
Cross-references Bosch 16982, DENSO Auto Parts 234-4809 and DENSO Auto Parts 234-4846 for the same application. See all 14.
Will it fit your vehicle?
Free return shipping if it doesn't fit.
Direct Fit Oxygen Sensor for Audi A8 Quattro
NTK Direct Fit Oxygen Sensor 25661 is a specific-fit, heated oxygen sensor built for downstream applications on the Audi A8 Quattro. It uses a threaded mounting design and a 4-wire configuration to match the original-style installation and signal requirements.
Key Features
- Direct fit design for specific application coverage
- Heated oxygen sensor for faster operating response
- 4-wire construction for OE-style signal control
- Threaded mounting type with 18 mm thread diameter
- 74.75 in. wiring harness length
Detailed Description
NTK 25661 is part of the Direct Fit Oxygen Sensor line, which focuses on application-specific replacement parts with OE-style fit, form, and function. NTK is established under the NGK family of products and is recognized as a major original equipment oxygen sensor supplier. This sensor is manufactured and tested to meet or exceed OE specifications, making it a direct replacement choice for downstream service on the Audi A8 Quattro. This part cross-references Bosch 16982 and DENSO Auto Parts 234-4809 for the same application.
Fits 2005-2009 Audi A8 Quattro, downstream. Fits 2005-2009 Audi A8 Quattro, downstream.
What It Is Used For
- Replacing a worn or slow-responding downstream oxygen sensor
- Restoring proper exhaust gas feedback to the engine control system
- Addressing sensor-related fault codes tied to mixture monitoring
- Correcting drivability issues caused by inaccurate oxygen readings
- Servicing OE-equivalent emissions control hardware
Installation Notes and Tips
Verify the connector, wire count, and threaded mounting style before installation. Confirm the downstream location and cylinder-bank application shown in the fitment notes for the Audi A8 Quattro. Use the part number 25661 to match the correct sensor configuration before removal of the original unit.
Quality Assurance
NTK states that these oxygen sensors are extensively tested during manufacturing to help ensure quality and reliability that meet or exceed OE specifications.
| Year | Make | Model | Liters | Cylinders | Position | Notes |
|---|---|---|---|---|---|---|
| 2009 | Audi | A8 Quattro | 6.0L | W12 | Downstream | Cyls. 7-9; B3S2; OE Equivalent Design; Direct Fit Oxygen Sensor |
| 2009 | Audi | A8 Quattro | 6.0L | W12 | Downstream | Cyls. 10-12; B4S2; OE Equivalent Design; Direct Fit Oxygen Sensor |
| 2008 | Audi | A8 Quattro | 6.0L | W12 | Downstream | Cyls. 7-9; B3S2; OE Equivalent Design; Direct Fit Oxygen Sensor |
| 2008 | Audi | A8 Quattro | 6.0L | W12 | Downstream | Cyls. 10-12; B4S2; OE Equivalent Design; Direct Fit Oxygen Sensor |
| 2007 | Audi | A8 Quattro | 6.0L | W12 | Downstream | Cyls. 7-9; B3S2; OE Equivalent Design; Direct Fit Oxygen Sensor |
| 2007 | Audi | A8 Quattro | 6.0L | W12 | Downstream | Cyls. 10-12; B4S2; OE Equivalent Design; Direct Fit Oxygen Sensor |
| 2006 | Audi | A8 Quattro | 6.0L | W12 | Downstream | Cyls. 7-9; B3S2; OE Equivalent Design; Direct Fit Oxygen Sensor |
| 2006 | Audi | A8 Quattro | 6.0L | W12 | Downstream | Cyls. 10-12; B4S2; OE Equivalent Design; Direct Fit Oxygen Sensor |
| 2005 | Audi | A8 Quattro | 6.0L | W12 | Downstream | Cyls. 10-12; B4S2; OE Equivalent Design; Direct Fit Oxygen Sensor |
| 2005 | Audi | A8 Quattro | 6.0L | W12 | Downstream | Cyls. 7-9; B3S2; OE Equivalent Design; Direct Fit Oxygen Sensor |
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