DTC P1143: Ho2S1 Lean Shift Monitoring - Bank 1 Or DTC P1163: Ho2S1 Lean Shift Monitoring - Bank 2: Description

WARNING: This page is about a different car, the 2002 Nissan Maxima and 2002 Infiniti I35. However, it is still accessible from the selected car via links, so may be relevant.

The front Heated Oxygen Sensors (HO2S1) are located in each front exhaust pipe, upstream of catalyst. They detect the amount of oxygen in the exhaust gas compared to the outside air. The front HO2S 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. The front HO2S signal is sent to the ECM. The ECM adjusts the injection pulse duration to achieve the ideal air-fuel ratio. The ideal air-fuel ratio occurs near the radical change from one volt to zero volts.

To judge the malfunction, the output from HO2S1 is monitored to determine whether the "rich" output is sufficiently high and whether the "lean" output is sufficiently low. When both the outputs are shifting to the lean side, the malfunction will be detected.