The heated oxygen sensors (HO2S) are used for fuel control and catalyst monitoring. Each HO2S compares the oxygen content of the surrounding air with the oxygen content of the exhaust stream. When the engine is started, the control module operates in an Open Loop mode, ignoring the HO2S signal voltage while calculating the air-to-fuel ratio. The control module supplies the HO2S with a reference, or bias voltage of about 450 mV. While the engine runs, the HO2S heats up and begins to generate a voltage within a range of 0-1,000 mV. This voltage will fluctuate above and below the bias voltage. Once sufficient HO2S voltage fluctuation is observed by the control module, Closed Loop is entered. The control module uses the HO2S voltage to determine the air-to-fuel ratio. An HO2S voltage that increases above bias voltage toward 1,000 mV indicates a rich fuel mixture. An HO2S voltage that decreases below bias voltage toward 0 mV indicates a lean fuel mixture.

The heating elements inside each HO2S heat the sensor to bring the sensor up to operating conditions faster. This allows the system to enter Closed Loop earlier and the control module to calculate the air-to-fuel ratio sooner.

Condition 1

Condition 2

Condition 3

Condition 1

The HO2S 1 signal voltage is between 400-520 mV, or 400-550 mV when the calculated exhaust temperature is warmer than 800°C (1,472°F).

Condition 2

The calculated internal resistance of the HO2S 1 is greater than 40,000 ohms when the calculated exhaust temperature is warmer than 600°C (1,112°F).

Condition 3

A corresponding HO2S 1 and HO2S 2 are greater than 200 mV during a decel fuel cut-off greater 3 seconds.

DTCs P0134 and P0154 are Type B DTCs.

DTCs P0134 and P0154 are Type B DTCs.

Schematic Reference

Engine Controls Schematics

Connector End View Reference

Component Connector End Views

Electrical Information Reference

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Control Module References for scan tool information

1. Engine idling, observe the appropriate scan tool HO2S voltage parameter. The voltage should fluctuate above and below the range of 350-550 mV.
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 HO2S.
2. Ignition ON, verify that a test lamp illuminates between the ignition circuit terminal D and ground.

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

3. Ignition OFF, connect a test lamp between the heater control circuit terminal E and B+.
4. Idle the engine, and verify the test lamp illuminates or flashes.

⇒	If the test lamp is always OFF, test the heater control circuit for an open/high resistance. If the circuit/connections test normal, replace the ECM.

5. Ignition ON, verify that the appropriate scan tool HO2S voltage parameter is between 350-500 mV.

⇒	If less than the specified range, test the signal circuit terminal B for a short to ground. If the circuit/connections test normal, replace the ECM.

⇒	If greater than the specified range, test the signal circuit terminal B for a short to voltage. If the circuit/connections test normal, replace the ECM.

6. Connect a 3 A fused jumper wire between the signal circuit terminal B and ground. Verify the scan tool HO2S voltage parameter is less than 60 mV.

⇒	If greater than the specified range, test the signal circuit for an open/high resistance. If the circuit/connections test normal, replace the ECM.

7. Connect a 3 A fused jumper wire between the signal circuit terminal B and the low reference circuit terminal A. Verify the scan tool HO2S voltage parameter is less than 60 mV.

⇒	If greater than the specified range, test the low reference circuit for an open/high resistance or for a short to voltage. If the circuit/connections test normal, replace the ECM.

8. Verify that none of the following conditions exist:

•	The HO2S is loose

•	Lean or rich condition.

•	Water intrusion in the HO2S harness connector

•	Low or high fuel system pressure--Refer to Fuel System Diagnosis.

•	Fuel that is contaminated--Refer to Alcohol/Contaminants-in-Fuel Diagnosis.

•	Fuel saturation of the evaporative emission (EVAP) canister

•	Exhaust leaks near the HO2S

•	Engine vacuum leaks

⇒	If you find any of the above conditions, repair as necessary.

9. If all circuits/connections test normal, replace the appropriate HO2S 1.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.