A Guide to Oxygen Sensors for the 2003-2012 INFINITI FX35
Solve check engine lights and improve performance by choosing the right oxygen sensor for your FX35's VQ35 engine.
- Your FX35 has four oxygen sensors; use the DTC code to identify which one has failed.
- For best results and to avoid compatibility issues, use Denso or NGK/NTK brand direct-fit sensors.
- Before replacing a sensor, inspect the wiring for melting and check for nearby exhaust leaks, as these can also trigger O2 sensor codes.
- Replacing the upstream passenger-side sensor (Bank 1, Sensor 1) is known to be difficult due to tight access near the firewall.
Symptoms of a Failing Oxygen Sensor
A bad oxygen sensor won't leave you stranded, but it will cause noticeable problems. The most common sign is a Check Engine Light on your dashboard. You may also experience reduced fuel economy, a rough or unstable idle, engine hesitation or misfires, and a general feeling of sluggish performance. In some cases, you might notice black smoke from the exhaust or a strong smell of fuel or rotten eggs.
Don't Ignore the Light
Driving for an extended period with a faulty oxygen sensor can lead to more expensive problems. An incorrect air-fuel mixture can eventually damage your catalytic converters, a very costly repair.
How Many Sensors Does My FX35 Have?
All 2003-2012 INFINITI FX35 models are equipped with four oxygen sensors. Understanding their locations is key to ordering the correct part.
- Bank 1 is on the passenger side of the engine.
- Bank 2 is on the driver's side of the engine.
- Sensor 1 is the upstream sensor, located before the catalytic converter (also called an Air/Fuel Ratio Sensor).
- Sensor 2 is the downstream sensor, located after the catalytic converter.
Therefore, the four specific locations are: Bank 1 Sensor 1 (Upstream/Passenger), Bank 2 Sensor 1 (Upstream/Driver), Bank 1 Sensor 2 (Downstream/Passenger), and Bank 2 Sensor 2 (Downstream/Driver).
Choosing the Right Aftermarket Oxygen Sensor
For a vehicle like the FX35, the brand of sensor you choose matters. While many brands are available, owner experiences and mechanic recommendations point to a clear hierarchy.
Tier 1: OEM-Equivalent Quality
Denso and NGK (NTK): These brands are the original equipment manufacturers for many Japanese vehicles, including Infiniti. They are widely considered the best choice for a direct-fit replacement that ensures proper performance and longevity without compatibility issues. Forum discussions consistently recommend sticking with Denso or NGK/NTK to avoid headaches.
Tier 2: Reputable Aftermarket
Bosch: Bosch is a massive sensor manufacturer and invented the automotive oxygen sensor. Their products are generally high quality. However, some mechanics and owners have noted that for Japanese applications, their aftermarket sensors can occasionally be less consistent than Denso or NGK. They remain a solid choice if a Tier 1 brand is unavailable.
Tier 3: Economy Brands
Walker, DriveWire, Facet, etc.: These brands offer a more budget-friendly price point. While they may function correctly, they do not have the same proven track record for long-term reliability and perfect electronic communication with the FX35's ECU as Denso or NGK. Using these can sometimes lead to persistent check engine lights or a shorter service life.
A Note on Universal Sensors
Universal sensors require you to cut your old sensor's connector and splice it onto the new sensor. While cheaper, this introduces a potential point of failure. For the FX35, it is strongly recommended to use 'Direct-Fit' sensors that come with the correct factory connector.
Known Issues and Technical Bulletins
No specific recalls have been issued by the NHTSA for oxygen sensor failure on the 2003-2012 FX35. However, there are common issues to be aware of:
- Wiring Damage: A common cause of sensor failure codes (like P0037) is the sensor's wiring harness making contact with the hot exhaust pipe, causing it to melt or short out. Always inspect the wiring and ensure it is routed safely away from the exhaust.
- Exhaust Leaks: A cracked exhaust manifold or a leak near the catalytic converter can allow extra oxygen into the exhaust stream, triggering a sensor code like P2A03 even if the sensor itself is good.
- Stubborn Codes: The code P2A03 (A/F Sensor Circuit Range/Performance) can sometimes be difficult to resolve. If a new, high-quality sensor doesn't fix the issue, a thorough check for intake and exhaust leaks is the next step.
Cost of Replacing an Oxygen Sensor on a 2003-2012 INFINITI FX35
| Item | Estimated Cost |
|---|---|
| New Aftermarket Sensor (Single) | $40 - $325 |
| New OEM Sensor (Single) | $150 - $350 |
| Shop Labor (Per Sensor) | $70 - $150 |
| Total Professional Replacement (Single Sensor) | $110 - $500+ |
Note: Costs are estimates. Labor can vary significantly based on which of the four sensors is being replaced. Upstream sensors, especially on the passenger side, are more difficult to access and will incur higher labor costs.
Frequently Asked Questions
Can I replace just one oxygen sensor?
Yes. You only need to replace the specific sensor that has failed and triggered a diagnostic trouble code. However, if the sensors are original and have high mileage (over 80,000 miles), it can be preventative maintenance to replace them in pairs (e.g., both upstream sensors at the same time).
What is the difference between an upstream and downstream sensor?
The upstream sensor (Sensor 1) is the most critical; it fine-tunes the engine's air-fuel ratio. The downstream sensor (Sensor 2) primarily checks the health of the catalytic converter. Upstream sensors are often a different, more complex design (wideband A/F) than downstream sensors (narrowband).
Do I need a special tool to replace an oxygen sensor?
Yes, it is highly recommended. An oxygen sensor socket is a special deep socket with a cutout on the side for the sensor's wire to pass through. Using a standard wrench can be difficult and may damage the sensor or wiring.
Can I clean my old oxygen sensor?
While some online sources suggest cleaning can temporarily fix a sluggish sensor, it is not a reliable or long-term solution for a sensor that has failed electronically. Once a sensor triggers a heater circuit or performance code, it needs to be replaced.
Helpful Videos
Technical Specifications
OEM Part Numbers: 22693-CD700 226A0-AM601 226A1-AM601 22693-1NA0A 22693-1MR0A
The 2003-2012 FX35 uses four heated oxygen sensors. The upstream sensors (Sensor 1) are wideband Air/Fuel ratio sensors, while the downstream sensors (Sensor 2) are traditional narrowband zirconia sensors. All are 4 or 5-wire sensors with direct-fit connectors.
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The information in this article is provided for general reference and educational purposes only. Vehicle specifications, procedures, and part compatibility can vary by production date, trim level, and region. Always consult your vehicle's factory service manual and verify part numbers before purchasing or performing repairs. Safety-critical components such as airbags, seat belts, and braking systems should be installed by a qualified professional.
- INFINITI FX35: