The heated oxygen sensors (HO2S) are used for fuel control and post catalyst monitoring. Each HO2S compares the oxygen content of the surrounding air with the oxygen content in the exhaust stream. The HO2S must reach operating temperature to provide an accurate voltage signal. A heating element inside the HO2S minimizes the time required for the sensor to reach operating temperature. Voltage is provided to the heater by the ignition 1 voltage circuit through a fuse. Ground is provided to the heater on the low control circuit by a low side driver within the control module. The control module monitors the current draw of the heater to determine if a failure is present.

The HO2S utilizes the following circuits:

P0135

P0141

The ECM detects that the HO2S heater current is less than 0.1 amp.

DTCs P0135 and P0141 are Type B DTCs.

DTCs P0135 and P0141 are Type B DTCs.

Schematic Reference

Engine Controls Schematics

Electrical Information Reference

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Control Module References for scan tool information

Important: It may take up to 8 minutes for the DTC to set.

1. Engine at normal operating temperature, operate the engine above 1,200 RPM for 30 seconds and then allow the engine to idle. DTCs P0135 or P0141 should not set.
2. Operate the vehicle within the Conditions for Running the DTC to verify the DTC does not reset. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.

1. Ignition OFF, disconnect the harness connector at the appropriate H02S sensor.
2. Ignition ON, verify that a test lamp illuminates between the ignition 1 voltage circuit terminal 4 and ground.

Important: The ignition 1 voltage circuit supplies voltage to other components. Make sure you test all circuits for a short to ground or test all components for being shorted that share the ignition 1 voltage circuit.

⇒	If the test lamp does not illuminate, test the ignition 1 voltage circuit for a short to ground or an open/high resistance. If the circuit tests normal and the ignition 1 voltage circuit fuse is open, test all components connected to the ignition 1 voltage circuit and replace as necessary.

3. Ignition OFF, connect a test lamp between the control circuit terminal listed below and 12 volts. The test lamp should not illuminate.

•	HO2S sensor 1 control circuit terminal 3

•	Euro IV HO2S sensor 1 control circuit terminal 2

⇒	If test lamp is always ON, test the control circuit for a short to ground. If the circuit tests normal, replace the ECM.

4. Engine running, verify the test lamp illuminates or flashes.

⇒	If the test lamp is always OFF, test the control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the ECM.

5. If all circuits test normal, test or replace the H02S sensor.

1. Ignition OFF, disconnect the harness connector at the appropriate HO2S sensor.
2. Test for 3-35 ohms of resistance between the signal terminal and low reference terminal listed below .

•	HO2S sensor 1 signal terminal 2

•	Euro IV HO2S sensor 1 signal terminal 1

•	HO2S sensor 1 low reference terminal 1

•	Euro IV HO2S sensor 1 low reference terminal 3

⇒	If not within the specified range, replace the HO2S sensor.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.