Front Heated Oxygen Sensors (HO2S)

Heated Oxygen Sensor (HO2S) Cutaway:

The Heated Oxygen Sensors are mounted in the exhaust system where they can monitor the oxygen content of the exhaust gas stream. The oxygen present in the exhaust gas reacts with the sensor to produce a voltage output. This voltage should constantly fluctuate from approximately 100 mV (high oxygen content - lean mixture) to 900 mV (low oxygen content - rich mixture). The heated oxygen sensor voltage can be monitored with a scan tool. By monitoring the voltage output of the oxygen sensor, the PCM calculates what fuel mixture command to give to the injectors (lean mixture - low HO2S voltage = rich command, rich mixture - high HO2S voltage = lean command).

When the PCM detects an HO2S signal circuit that is low, the PCM will set the following DTCs:
^ DTC P0131 HO2S Circuit Low Voltage Bank 1 Sensor 1.
^ DTC P0151 HO2S Circuit Low Voltage Bank 2 Sensor 1.
^ DTC P0137 HO2S Circuit Low Voltage Bank 1 Sensor 2.
^ DTC P0157 HO2S Circuit Low Voltage Bank 2 Sensor 2.

When the PCM detects an HO2S signal circuit that is high, the PCM will set the following DTCs:
^ DTC P0132 HO2S Circuit High Voltage Bank 1 Sensor 1.
^ DTC P0152 HO2S Circuit High Voltage Bank 2 Sensor 1.
^ DTC P0138 HO2S Circuit High Voltage Bank 1 Sensor 2.
^ DTC P0158 HO2S Circuit High Voltage Bank 2 Sensor 2.

When the PCM detects no HO2S activity, the PCM will set the following DTCs:
^ DTC P0134 HO2S Insufficient Activity Bank 1 Sensor 1.
^ DTC P0154 HO2S Insufficient Activity Bank 2 Sensor 1.
^ DTC P0140 HO2S Insufficient Activity Bank 1 Sensor 2.
^ DTC P0160 HO2S Insufficient Activity Bank 2 Sensor 2.

A fault in the heated oxygen sensor heater element or its ignition feed or ground will result in an increase in time to Closed Loop fuel control. This may cause increased emissions, especially at start-up. When the PCM detects a malfunction in the HO2S heater circuits, the following DTCs will set:
^ DTC P0135 Heater Circuit Bank 1 Sensor 1.
^ DTC P0155 Heater Circuit Bank 2 Sensor 1.
^ DTC P0141 Heater Circuit Bank 1 Sensor 2.
^ DTC P0161 Heater Circuit Bank 2 Sensor 2.

The PCM also has the ability to detect the following HO2S problems:
^ HO2S response
^ Switching
^ Transition time
^ Incorrect ratio voltage

The PCM stores a DTC that indicates degraded HO2S performance if any of the above is detected.