Diagnostic Instructions

DTC Descriptors

DTC P0131: HO2S Circuit Low Voltage Sensor 1

DTC P0132: HO2S Circuit High Voltage Sensor 1

DTC P0134: HO2S Circuit Insufficient Activity Sensor 1

DTC P0151: HO2S Circuit Low Voltage Sensor 2

DTC P0152: HO2S Circuit High Voltage Sensor 2

DTC P0154: HO2S Circuit Insufficient Activity Sensor 2

Diagnostic Fault Information

Circuit	Short to Ground	Open/High Resistance	Short to Voltage	Signal Performance
HO2S Signal	P0131, P0151	P0134, P0154	P0132, P0152	--
Low Reference	--	P0134, P0154	P0132, P0152	--

Typical Scan Tool Data

HO2S 1 and 2

Circuit	Short to Ground	Open	Short to Voltage
Operating Conditions: Engine operating in Closed Loop Parameter Normal Range: Fluctuates above and below 350-500 mV
HO2S 1 and 2 Signal	0 mV	400-415 mV	1000 mV
Low Reference	--	400-415 mV	1000 mV

Circuit Description

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:

Conditions for Running the DTC

Conditions for Setting the DTC

DTC P0131 or P0151

The engine control module (ECM) detects that the HO2S voltage is less than 80 mV.

DTC P0132 or P0152

The ECM detects that the HO2S voltage is greater than 1,050 mV.

DTC P0134 or P0154

The ECM detects that the HO2S voltage is between 350-550 mV for 100 seconds.

Action Taken when the DTC Sets

Conditions for Clearing the MIL/DTC

DTCs  P0131, P0132, P0134, P0151, P0152, and P0154 are Type B DTCs.

Reference Information

Schematic Reference

Engine Controls Schematics

Connector End View Reference

Electrical Information Reference

DTC Type Reference

Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Engine Control Module Scan Tool Information

Circuit/System Verification

1. Engine idling, observe the scan tool heated oxygen sensor voltage parameters. The reading 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.

Circuit/System Testing

1. Ignition OFF, disconnect the harness connector at the applicable HO2S.
2. Ignition OFF, test for less than 5 ohms between the low reference circuit terminal A and ground.

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

3. Engine idling, verify the applicable HO2S parameter is between 350-500 mV.

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

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

4. Ignition OFF, install a 3A fused jumper wire between the signal circuit terminal B and the low reference circuit terminal A. Engine idling, verify the scan tool HO2S parameter is less than 60 mV.

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

5. Verify none of the following conditions exist:

•	Lean or 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

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

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

•	Exhaust leaks near the HO2S

•	Engine vacuum leaks

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

6. If all circuits test normal, replace the applicable HO2S.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.