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.

The HO2S utilizes the following circuits:

The engine control module (ECM) detects that the HO2S voltage is greater than 550 mV during DFCO mode.

DTC P2097 is a Type B DTC.

DTC P2097 is a Type B DTC.

Schematic Reference

Engine Controls Schematics

Connector End View Reference

Electrical Information Reference

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

1. Engine idling, observe the scan tool HO2S parameter. The reading should fluctuate above and below 350-550 mV.
2. If the vehicle passes the Circuit/System Verification test, then operate the vehicle within the conditions for running the DTC. You may also operate the vehicle within the conditions that are captured in the Freeze Frame/Failure Records Data List.

1. Ignition OFF, disconnect the harness connector at the appropriate HO2S.
2. Ignition ON, verify the scan tool HO2S parameter is between 350-500 mV.

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

3. Verify none of the following conditions exist:

•	Rich fuel injectors--Refer to Fuel Injector Balance Test with Special Tool or Fuel Injector Balance Test with Tech 2 .

•	Water intrusion in the HO2S harness connector

•	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 emissions (EVAP) canister

•	Restricted exhaust

•	Contaminated HO2S - Silicon

⇒	If a condition is found, repair as necessary.

4. If all circuits test normal, test or replace the applicable HO2S.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.