Pre-CAT Heated Oxygen Sensors

Description:

NOTE: The enclosed numbers in the text refer to the numbers in the image.

DESCRIPTION
The Heated Oxygen Sensor (HO2S) produces a voltage that varies between 100 mV and 900 mV under the normal operating conditions. On the Catera, the full operating range of the HO2S circuit is approximately from 200 mV to 1,200 mV. The Engine Control Module (ECM) monitors this voltage and determines if the exhaust is lean or rich.

OPERATION
The oxygen sensor voltage is high when the exhaust is rich, and low when the exhaust is lean. The ECM constantly monitors the HO2S signal during the closed loop operation and compensates for a rich or lean condition by decreasing or increasing the injector pulse width as necessary.

The following DTCs indicate that the ECM has detected an HO2S signal voltage that is outside of the normal operating range of the sensor:
^ DTC P0130 - HO2S Circuit - Bank 1 Sensor 1(2)
^ DTC P0136 - HO2S Circuit - Bank 2 Sensor 1 (3)
^ DTC P0150 - HO2S Circuit - Bank 1 Sensor 2 (1)
^ DTC P0156 - HO2S Circuit - Bank 2 Sensor 2 (4)

The following DTCs indicate that the ECM has detected an HO2S signal voltage that remains excessively low:
^ DTC P0131 - HO2S Circuit Low Voltage - Bank 1 Sensor 1 (2)
^ DTC P0137 - HO2S Circuit Low Voltage - Bank 2 Sensor 1(3)
^ DTC P0151 - HO2S Circuit Low Voltage - Bank 1 Sensor 2 (1)
^ DTC P0157 - HO2S Circuit Low Voltage - Bank 2 Sensor 2 (4)

The following DTCs indicate that the ECM has detected an HO2S signal voltage that remains excessively high:
^ DTC P0132 - HO2S Circuit High Voltage - Bank 1 Sensor 1 (2)
^ DTC P0138 - HO2S Circuit High Voltage - Bank 2 Sensor 1(3)
^ DTC P0152 - HO2S Circuit High Voltage - Bank 1 Sensor 2 (1)
^ DTC P0158 - HO2S Circuit High Voltage - Bank 2 Sensor 2 (4)

A fault in the heated oxygen sensor heater element or the related ignition feed or ground will result in an increase in time to a Closed Loop fuel control. This may cause increased emissions, especially at start-up. The following DTCs indicate that the ECM detects a problem with an HO2S Heater:
^ DTC P0135 - HO2S Heater Circuit - Bank 1 Sensor 1 (2)
^ DTC P0141 - HO2S Heater Circuit - Bank 2 Sensor 1(3)
^ DTC P0155 - HO2S Heater Circuit - Bank 1 Sensor 2 (1)
^ DTC P0161 - HO2S Heater Circuit - Bank 2 Sensor 2 (4)

The ECM also has the ability to evaluate HO2S response time and whether or not there is sufficient signal activity. If a problem is detected, the ECM will store a DTC indicating degraded HO2S performance.