Heated Oxygen Sensor

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

CAUTION: DO NOT attempt to measure oxygen sensor output voltage using a conventional voltmeter. Current drain of voltmeter could damage sensor. Oxygen sensor voltage signal can be measured using a 10-megohm (minimum input impedance) digital voltmeter.

The HO2S produces a voltage that varies between 0.1-0.9 volt under normal operating conditions. The Powertrain Control Module (PCM) monitors this voltage and determines if the exhaust is lean or rich. If the voltage input at the PCM is about 0.1 volt the exhaust is lean, and if the voltage input is about 0.9 volt, the exhaust is rich. The PCM constantly monitors the HO2S 1 signal during closed loop operation and compensates for a rich or lean condition by decreasing or increasing the injector pulse width as necessary. Heated Oxygen Sensors (HO2S) are installed before (pre-catalyst) and after (post-catalyst) the TWC. Voltage variations between the sensors allow the PCM to determine the performance of the TWC catalyst. For more information, see CATALYST MONITOR DIAGNOSTIC OPERATION under SELF-DIAGNOSTIC SYSTEM.