The oxygen sensor (O2S) is used for fuel control. The O2S 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 O2S signal voltage while calculating the air-to-fuel ratio. The control module supplies the O2S with a reference, or bias voltage of about 450 mV. While the engine runs, the O2S 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 O2S voltage fluctuation is observed by the control module, Closed Loop is entered. The control module uses the O2S voltage to determine the air-to-fuel ratio. An O2S voltage that increases above bias voltage toward 1,000 mV indicates a rich fuel mixture. An O2S voltage that decreases below bias voltage toward 0 mV indicates a lean fuel mixture.

P0131

The engine control module (ECM) detects that the O2S voltage is less than 50 mV for 25 seconds.

P0132

The ECM detects that the O2S voltage is more than 952 mV for 25 seconds.

DTCs P0131 and P0132 are Type A DTCs.

DTCs P0131 and P0132 are Type A DTCs.

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. With the engine running, observe the oxygen sensor (O2S) voltage parameter. The reading should fluctuate above and below the range of 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 FreezeFrame/Failure Records List.

1. Ignition OFF, disconnect the harness connector of the O2S .
2. Ignition ON, verify that the O2S parameter is between 350-500 mV.

⇒	If less than 350 mV, test the signal circuit of the O2S for a short to ground. If the circuit/connections test normal, ECM.

⇒	If greater than 500 mV, test the signal circuit of the O2S for a short to voltage. If the circuit/connections test normal, replace the ECM.

Important: The test lamp is used to load the circuit and may not illuminate.

3. Connect a test lamp between the low reference circuit of the O2S and the positive terminal of the battery.
4. Ignition ON, test for less than 0.1 volt between the low reference circuit of the O2S and the negative terminal of the battery.

⇒	If greater than 0.1 volt, test the low reference circuit of the O2S for a short to voltage or an open/high resistance. If the circuit/connections test normal, replace the ECM.

5. Install a 3-amp fused jumper wire between the signal circuit and the low reference circuit of the O2S and verify the O2S parameter is less than 60 mV.

⇒	If greater than 60 mV, test the signal circuit of the O2S for an open/high resistance. If the circuit/connections test normal, replace the ECM.

6. Verify that the following conditions do not exist:

•	Lean or rich fuel injectors--Refer to Fuel Injector Balance Test with Special Tool .

•	Water intrusion in the O2S 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 O2S.

•	Engine vacuum leaks.

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

7. If all circuits/connections test normal, replace the O2S .

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.