Circuit Description: Notes

The DTC P0134 Heated Oxygen Sensor (HO2S) Circuit Sensor 1 diagnostic detects an inactive or fixed HO2S signal. The HO2S produces a voltage that varies between 100-900 mV. The powertrain control module (PCM) monitors this voltage and determines by the exhaust gas oxygen content whether the air/fuel mixture is rich or lean. When the voltage input at the PCM is about 100 mV, the HO2S is indicating a lean air/fuel mixture. When the voltage input is about 900 mV, the HO2S is indicating rich air/fuel mixture. The PCM constantly monitors the HO2S signal during Closed Loop operation and compensates for the rich or the lean condition by decreasing or increasing fuel injector pulse width. A DTC P0134 may set if the HO2S 1 voltage remains excessively high or low for an extended period of time.