In a 2009 Honda Accord, the oxygen sensors sit along the exhaust system. The four-cylinder model uses two sensors—one before the catalytic converter and one after it—while the V6 model uses four sensors—two upstream and two downstream, one pair for each bank.
Engine configurations and sensor counts
The dealer service manual and owner resources describe the sensor placements by engine type. Below are the typical locations you will encounter beneath the car.
4-cylinder 2.4L (K-series) engine
For the 4-cylinder Accord, expect two O2 sensors on the exhaust path.
Locations:
- Upstream O2 sensor (Bank 1 Sensor 1): installed in the downpipe just after the exhaust manifold, before the catalytic converter. It is usually accessible from underneath the vehicle.
- Downstream O2 sensor (Bank 1 Sensor 2): located after the catalytic converter on the downpipe, also accessible from below or the passenger-side wheel well area depending on model year.
In short, the 4-cylinder uses two sensors, positioned on the exhaust pipe before and after the catalytic converter.
V6 3.5L engine
The V6 configuration splits oxygen sensors by bank, with a total of four sensors.
Locations:
- Bank 1 upstream O2 sensor (Sensor 1): located on the exhaust manifold or the pipe leading to the first catalytic converter on Bank 1.
- Bank 1 downstream O2 sensor (Sensor 2): located after Bank 1’s catalytic converter on the downstream pipe.
- Bank 2 upstream O2 sensor (Sensor 3): located on the exhaust path for Bank 2, before its catalytic converter.
- Bank 2 downstream O2 sensor (Sensor 4): located after Bank 2’s catalytic converter on the downstream pipe.
For the V6, there are two separate sensor sets, one on each side of the engine, corresponding to each exhaust bank.
Practical notes and safety tips
Working on O2 sensors requires the engine and exhaust to be cool, and you will need the right tools (an O2 sensor socket and wrench). Disconnect the vehicle’s battery if you’ll be working near electrical components, and use anti-seize on new sensors if recommended by the manufacturer. If you’re unsure of the engine configuration, consult the owner’s manual or VIN-based service information to confirm sensor counts and locations.
Summary
The O2 sensor locations on a 2009 Honda Accord vary by engine. The 4-cylinder model has two sensors—upstream and downstream—located along the exhaust pipe before and after the catalytic converter. The V6 model uses four sensors, with one upstream and one downstream sensor on each exhaust bank. Identifying the exact positions will help when performing diagnostics or replacements, and consulting the service manual or a shop manual is recommended for precise steps and wiring orientation.