DTC P1143: Bank 1 Heated Oxygen Sensor 1 - Lean Shift Monitoring Or DTC P1163: Bank 2 Heated Oxygen Sensor 1 - Lean Shift Monitoring : Description

WARNING: This page is about a different car, the 2003 Nissan Pathfinder. However, it is still accessible from the selected car via links, so may be relevant.

The front Heated Oxygen Sensors (HO2S 1) are located in each front exhaust pipe, upstream of catalyst. They detect the amount of oxygen in exhaust gas compared to outside air. HO2S 1 has a closed-end tube made of ceramic zirconia. The zirconia generates voltage from about one volt in richer conditions to zero volts in leaner conditions. HO2S 1 signal is sent to the ECM. ECM adjusts injection pulse duration to achieve ideal air/fuel ratio. The ideal air/fuel ratio occurs near the radical change from one volt to zero volts.

To judge the malfunction, output from HO2S 1 is monitored to determine whether "rich" output is sufficiently high and whether "lean" output is sufficiently low. When both outputs are shifting to lean side, malfunction will be detected.