Two oxygen sensors are used on the 2.4-liter four-cylinder version, while the 3.0-liter V6 configuration uses four sensors—two upstream and two downstream. The exact count depends on which engine your 2004 Accord has.
Engine configurations and sensor counts
The 2004 Accord was offered with two main engines, and each has a different exhaust layout that determines the number of O2 sensors installed from the factory.
Four-cylinder 2.4L engine
In the 2004 Accord equipped with the 2.4L four-cylinder engine, the exhaust system typically includes a single catalytic converter. This setup uses two O2 sensors: one upstream (pre-cat) and one downstream (post-cat).
- Upstream O2 sensor (pre-cat) for monitoring air-fuel mixture before the catalytic converter
- Downstream O2 sensor (post-cat) for monitoring catalytic converter efficiency
Conclusion: The 2.4L four-cylinder configuration has two oxygen sensors in stock form.
V6 3.0L engine
The 2004 Accord with the 3.0L V6 typically features a dual-exhaust layout with two catalytic converters. This arrangement requires four O2 sensors: two upstream (one for each bank) and two downstream (one after each cat).
- Upstream O2 sensor - Bank 1 (pre-cat)
- Downstream O2 sensor - Bank 1 (post-cat)
- Upstream O2 sensor - Bank 2 (pre-cat)
- Downstream O2 sensor - Bank 2 (post-cat)
Conclusion: The 3.0L V6 configuration has four oxygen sensors in stock form.
Summary
For a 2004 Honda Accord, the total number of oxygen sensors depends on the engine. The 2.4L four-cylinder uses two sensors, while the 3.0L V6 uses four sensors. When diagnosing or replacing sensors, verify your vehicle’s exact engine and exhaust configuration, as aftermarket systems or regional specs can affect sensor placement and count.