Volt

DTC P0131, P0132, P0134, P0137, P0138, or P0140

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 engine control module (ECM) operates in an open loop mode, ignoring the HO2S signal voltage while calculating the air to fuel ratio. While the engine runs, the HO2S heats up and begins to generate a voltage within a range of 0-1,900 mV. 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 toward 1,000 mV indicates a rich fuel mixture. An HO2S voltage that decreases 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.

This ECM uses a high bias voltage on the high and low signal circuits of the HO2S. The voltage measured between the low signal terminal and ground varies based on the temperature of the sensor and will typically be between 0-1,000 mV under normal operating conditions. The value of the high signal terminal measured to ground is equal to the value of the low signal measured to ground plus the 1,900 mV bias between the low signal and the high signal. In closed loop, the sensor functions in the same voltage range as systems with the low bias voltage. In open loop or open circuit conditions, the high bias voltage is present and takes the voltage outside of the normal operating range for easier fault detection.

P0131 or P0137

P0132 or P0138

P0134 or P0140

P0131 or P0137

The ECM detects that the HO2S voltage is less than 50 mV for greater than 48 s for DTC P0131 or 54 s for DTC P0137.

P0132 or P0138

The ECM detects that the HO2S voltage is greater than 1,050 mV for greater than 13 s.

P0134 or P0140

The ECM detects that the HO2S voltage is greater than 1,700 mV for greater than 25 s.

DTCs P0131, P0132, P0137, and P0138 are Type B DTCs.

DTCs P0131, P0132, P0137, and P0138 are Type B DTCs.

Schematic Reference

Engine Controls Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Hybrid Modes of Operation Description

Electrical Information Reference

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Control Module References for scan tool information

1. Vehicle in Service Mode, observe the DTC information with a scan tool. Verify no HO2S heater DTCs are set.

⇒	If a DTC is set, refer to Diagnostic Trouble Code (DTC) List - Vehicle .

2. Engine running, observe the appropriate scan tool HO2S 1 or 2 voltage parameter. The reading should vary between 50-1,050 mV.
3. 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. Vehicle OFF, disconnect the harness connector at the appropriate B52 HO2S.
2. Vehicle in Service Mode, observe the scan tool HO2S 1 or 2 voltage parameter. The parameter should display between 1,850-1,950 mV.

⇒	If less than the specified range, test the high and low signal circuits for a short to ground. If both signal circuits test normal, replace the K20 ECM.

3. Test for 1,850-3,000 mV between the high signal circuit terminal listed below and ground.

•	B52 HO2S 1 high signal terminal 4

•	B52 HO2S 2 high signal terminal B

⇒	If less than the specified range, test the high signal circuit for an open/high resistance. If the circuit tests normal, replace the K20 ECM.

⇒	If greater than the specified range, test the high signal circuit for a short to voltage. If the circuit tests normal, replace the K20 ECM.

4. Connect a 3 A fused jumper wire between the high signal circuit and low signal circuit terminals listed below:

•	B52 HO2S 1 high signal circuit terminal 4 to low signal circuit terminal 3

•	B52 HO2S 2 high signal circuit terminal B to low signal circuit terminal A

Note: The low signal circuit is tied to a pull-up circuit within the ECM. A voltage of 0-1,100 mV on the low signal circuit is normal.

5. Verify the scan tool HO2S 1 or 2 voltage parameter displays 0.0 mV.

⇒	If greater than the specified range, test the low signal circuit for an open/high resistance or for a short to voltage. If the circuit tests normal, replace the K20 ECM.

6. Verify none of the following conditions exist:

•	Lean or rich fuel injectors--Refer to Fuel Injector Solenoid Coil Test

•	Water intrusion in the B52 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

•	Engine vacuum leaks

•	Engine oil consumption--Refer to Oil Consumption Diagnosis

•	Engine coolant consumption--Refer to Loss of Coolant

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

7. If all circuits test normal, test or replace the appropriate B52 HO2S.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.