There are four oxygen sensors on a 2004 Honda Accord V6: two upstream sensors before the catalytic converters and two downstream sensors after them.
The 2004 Accord with the 3.0-liter V6 uses a dual-bank exhaust system. Each bank has its own catalytic converter, and each converter is monitored by a pair of O2 sensors. This configuration helps the engine control unit precisely adjust the air-fuel ratio and monitor catalyst efficiency across the exhaust stream.
Sensor layout and purpose
To help you locate them on the engine, note that the 3.0L V6 uses two exhaust banks, each with an upstream and downstream O2 sensor. This means four sensors total, arranged two per bank.
Bank-specific arrangement
Each bank in the V6 engine has its own catalytic converter and pair of O2 sensors. Locating and replacing these sensors requires attention to the bank they monitor.
- Bank 1 upstream sensor (pre-cat)
- Bank 1 downstream sensor (post-cat)
- Bank 2 upstream sensor (pre-cat)
- Bank 2 downstream sensor (post-cat)
These four sensors provide feedback to the engine control unit (ECU) to regulate the air-fuel mixture and to monitor the efficiency of the catalytic converters.
Maintenance considerations
O2 sensors are wear items and can fail with age, causing symptoms such as reduced fuel economy or a CHECK ENGINE light. If a diagnostic code points to the O2 sensors, diagnostic testing and replacement of the affected sensor(s) may be necessary.
Summary
The 2004 Honda Accord V6 typically uses four O2 sensors—two upstream and two downstream—one pair for each bank of the dual-bank exhaust system. This arrangement supports real-time fuel management and catalytic monitoring.