The wide band heated oxygen sensor (HO2S) measures the amount of oxygen in the exhaust system and provides more information than the switching style HO2S. The wide band sensor consists of an oxygen sensing cell, an oxygen pumping cell, and a heater. The exhaust gas sample passes through a diffusion gap between the sensing cell and the pumping cell. The engine control module (ECM) supplies a voltage to the HO2S and uses this voltage as a reference to the amount of oxygen in the exhaust system. An electronic circuit within the ECM controls the pump current through the oxygen pumping cell in order to maintain a constant voltage in the oxygen sensing cell. The ECM monitors the voltage variation in the sensing cell and attempts to keep the voltage constant by increasing or decreasing the amount of current flow, or oxygen ion flow, to the pumping cell. By measuring the amount of current required to maintain the voltage in the sensing cell, the ECM can determine the concentration of oxygen in the exhaust. The HO2S voltage is displayed as a lambda value. A lambda value of 1 is equal to a stoichiometric air fuel ratio of 14.7:1. Under normal operating conditions, the lambda value will remain around 1. When the fuel system is lean, the oxygen level will be high and the lambda signal will be high or greater than 1. When the fuel system is rich, the oxygen level will be low, and the lambda signal will be low or less than 1. The ECM uses this information to maintain the correct air/fuel ratio. If the ECM detects that the HO2S signal voltage is low, this DTC sets.

The internal ECM HO2S voltage is less than a threshold for greater than 4 seconds.

DTCs P0131 and P0151 are Type B DTCs.

DTCs P0131 and P0151 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 at normal operating temperature, verify the scan tool Loop Status Bn 1 Sen 1 and Loop Status Bn 2 Sen 1 parameters display Closed Loop.
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 are captured in the Freeze Frame/Failure Records Data List.

1. Ignition OFF, disconnect the harness connector at the appropriate HO2S sensor.
2. Ignition ON, test for 350-550 mV between the reference voltage circuit terminal 3 and the low reference circuit terminal 1.

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

⇒	If greater than the specified range, test the reference voltage circuit and the low reference circuit for a short to voltage. If the circuits test normal, replace the ECM.

3. Connect a test lamp between the input pump current circuit terminal 4 and B+.

⇒	If the test lamp illuminates, test the input pump current circuit and the pump current circuit for a short to ground. If the circuits test normal, replace the ECM.

4. Verify that the following conditions do not exist:

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

•	Low 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.

5. If all circuits test normal, replace the HO2S sensor.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.