P0131

CIRCUIT DESCRIPTION

The Heated Oxygen Sensor (HO2S) produces a voltage that varies between -100 mV and 900 mV under normal operating conditions. On the Catera, the full operating range of the HO2S circuit is approximately from -406 mV to 1124 mV. The Engine Control Module (ECM) monitors this voltage and determines if the exhaust is lean or rich. The oxygen sensor voltage is high when the exhaust is rich, and low when the exhaust is lean. The ECM constantly monitors the HO2S signal during the closed loop operation and compensates for a rich or lean condition by decreasing or increasing the injector pulse width as necessary. If the ECM detects an excessively low HO2S voltage, this DTC will set.

CONDITIONS FOR RUNNING THE DTC

^ No DTCs are set.

^ The HO2S heater is on for longer than 200 seconds.

^ The secondary AIR diagnostic is not running.

CONDITIONS FOR SETTING THE DTC

^ The HO2S voltage is below -148 mV.

^ The above condition met for longer than 0.2 seconds.

ACTION TAKEN WHEN THE DTC SETS

The ECM illuminates the Malfunction Indicator Lamp (MIL) and records the operating conditions in the Freeze Frame on the second consecutive drive trip that the diagnostic runs and fails.

CONDITIONS FOR CLEARING THE MIL/DTC

^ The ECM turns off the MIL after three consecutive drive trips that the diagnostic runs and does not fail.

^ A History DTC clears after forty consecutive warm-up cycles if no failures report by this diagnostic or any other emission related diagnostic.

^ The ECM battery voltage is interrupted.

^ The scan tool clears the MIL/DTC.

DIAGNOSTIC AIDS

Use the Connector Test Adapter Kit J 35616-A for any test that requires probing the ECM harness connector or a component harness connector. Using this kit will prevent damage to the harness connector terminals.

Check for the following conditions:

^ The sensor pigtail or the harness may be mis-positioned and contacting the exhaust system.

^ Heated oxygen sensor wiring. Check for the following conditions:

- Inspect the harness connectors for the following conditions:

- Backed out terminals

- Improper mating

- Broken locks

- Improperly formed or damaged terminals

- Poor terminal to wire connection

- Corrosion and water intrusion

Refer to Overall Vehicle Information / Diagrams / Diagnostic Aids for Checking Terminal Contact procedure.

An oxygen supply inside of the HO2S is necessary for a proper operation. This supply of oxygen is provided through the HO2S wires. All of the HO2S wires and connections should be inspected for any breaks or any contamination. If any wiring repairs need to be made, refer to Overall Vehicle Information / Diagrams / Diagnostic Aids for repair procedures.

- Poor ECM to engine grounds.

- If the above are OK, the HO2S may be at fault.

TEST DESCRIPTION

The number(s) below refer to the step numbers on the diagnostic table:

2. The engine must be at the normal operating temperature before performing this test.

3. Using the Freeze Frame data may aid in locating an intermittent condition. If the DTC cannot be duplicated, review the information in the Freeze Frame. Try to operate the vehicle within the same freeze frame conditions (the RPM, the MAF, the vehicle speed, the temperature etc.) that were noted. This process may help in order to recreate the malfunction.