Two for the 2.4-liter four-cylinder version, and four for the 3.0-liter V6 version.
The 2004 Honda Accord offered both a 2.4L inline-4 and a 3.0L V6. Oxygen sensors (O2 sensors) monitor exhaust gas composition before and after the catalytic converter to regulate the air-fuel mix and track catalytic efficiency. The number of sensors depends on the engine configuration and exhaust arrangement.
Sensor counts by engine configuration
2.4L inline-4 engine
For the four-cylinder model, the exhaust system typically uses two O2 sensors: one upstream of the catalytic converter and one downstream.
- Two O2 sensors total: upstream (pre-cat) and downstream (post-cat).
This two-sensor setup is standard for the 2.4L Accord and is sufficient for the onboard diagnostics system to monitor emissions performance.
3.0L V6 engine
The V6 version features two exhaust banks, each with its own catalytic converter, resulting in four O2 sensors in total—two per bank (upstream and downstream).
- Four O2 sensors total: Bank 1 upstream, Bank 1 downstream, Bank 2 upstream, Bank 2 downstream.
If you’re inspecting or replacing sensors on the V6, count sensors per bank and verify wiring and connectors for each sensor location.
Summary
In brief, the 2004 Honda Accord uses two O2 sensors on the 2.4L four-cylinder and four O2 sensors on the 3.0L V6. This arrangement reflects the single-bank vs. dual-bank exhaust layouts, with upstream and downstream sensors for each catalytic converter in the V6 version.