Two on the 2.5-liter four-cylinder version and four on the 3.5-liter V6.
Engine options and sensor counts
The 2009 Altima was offered with two engine choices, and the number of oxygen sensors follows the engine design. The four-cylinder version uses a simpler exhaust with two sensors, while the V6 setup uses a dual-bank exhaust that requires more sensors.
- 2.5-liter four-cylinder: two O2 sensors total — one upstream (pre-catalytic converter) and one downstream (post-catalytic converter).
- 3.5-liter V6: four O2 sensors total — two upstream (one for each bank) and two downstream (one for each bank).
Overall, the Altima’s O2 sensor count depends on the engine: two sensors for the 2.5L model, four sensors for the 3.5L model.
Locating and maintaining O2 sensors
On the four-cylinder Altima, expect the upstream sensor near the exhaust manifold and the downstream sensor after the catalytic converter on the single exhaust line. On the V6 model, sensors are placed on both banks of the exhaust system, with one upstream and one downstream sensor per bank. Since sensor placement can vary by production date or regional specification, checking the vehicle’s VIN or service manual is recommended for precise locations.
Maintenance tips
When diagnosing O2 sensor-related issues, diagnostic trouble codes (DTCs) such as P013x (B1S1, etc.) commonly point to failed sensors. Replacing sensors in matched pairs on each bank (especially on the V6) helps ensure accurate readings and smooth engine performance.
Summary
In summary, the 2009 Nissan Altima's O2 sensor count is two for the 2.5L four-cylinder and four for the 3.5L V6. Always verify engine type to determine the exact number for a given vehicle.
Where is the O2 sensor located on a 2009 Nissan Altima?
The primary oxygen sensor (air/fuel ratio sensor) is in the intake manifold below the heat shield-2.5L engine shown.
How many oxygen sensors does a 2009 Nissan Altima have?
Altima 2.5L L4 2007 2008 2009 2010（Federal Emissions）. Oxygen Sensor. 2 x Oxygen Sensors.
How can I tell which 02 sensor is bad?
Set the multimeter to DC voltage and probe the sensor's signal wire. A good sensor fluctuates between 0.1V and 0.9V. A steady reading or no voltage means the sensor is bad.
Is there a difference between bank 1 sensor 1 and bank 2 sensor 1?
Bank 1 Sensor 1 = Upstream sensor on the side with Cylinder 1. Bank 1 Sensor 2 = Downstream sensor on the side with Cylinder 1. Bank 2 Sensor 1 = Upstream sensor on the opposite side.