P0137

CIRCUIT DESCRIPTION
The heated oxygen sensor (HO2S) is a sensor used to detect oxygen-content in the exhaust. The powertrain control module (PCM) supplies the sensor with a signal circuit and a ground circuit. The PCM supplies a bias voltage between the circuits. The sensor varies the voltage based on the oxygen content in the exhaust. When the exhaust stream is lean (more oxygen), the sensor produces a low voltage signal. When the exhaust stream is rich (less oxygen), the sensor produces a high voltage signal. The PCM monitors the HO2S signal during Closed Loop. To correct for rich or lean conditions, the PCM adjusts the injector pulse width.

CONDITIONS FOR RUNNING THE DTC
^ DTCs P0101, P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0121, P0122, P0123, P0125, P0201- P0208, P0410, P0412, P0418, P0419, P0440, P0442, P0443, P0446, P0449, P1415, P1416, or P1441 are not set.
^ The throttle position angle is between 3-25 percent.
^ The system voltage is between 9-18 volts.
^ The Closed Loop fuel control is enabled.
^ The air/fuel ratio is between 14.4 to 14.9.
^ The EGR flow diagnostic test is not active.
^ The AIR diagnostic test is not active.
^ The injectors are not disabled.
^ The catalyst diagnostic test is not active.
^ The conditions above met for 5 seconds.

CONDITIONS FOR SETTING THE DTC
^ HO2S bank 1 sensor 2 signal voltage remains below 9 mV for approximately 5 seconds during normal Closed Loop fuel control.

OR

^ Bank 1 sensor 2 HO2S signal voltage remains below 575 mV during power enrichment operation for more than 8 seconds.

ACTION TAKEN WHEN THE DTC SETS
^ The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
^ The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

CONDITIONS FOR CLEARING THE MIL/DTC
^ The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
^ A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
^ A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
^ Clear the MIL and the DTC with a scan tool.

DIAGNOSTIC AIDS

NOTE:
^ Refer to Heated Oxygen Sensor (HO2S) Wire Repair Notice in Service Precautions.
^ Refer to Connector Test Adapter Kit J 35616-A Notice in Service Precautions.

Check for the following conditions:
^ The HO2S wire routing-The sensor wiring may be routed incorrectly and contacting the exhaust system.
^ Exhaust leaks-Exhaust leaks may cause outside air to be drawn into the exhaust gas stream, and pass the HO2S. This causes the HO2S signal to indicate a false lean condition.
^ For intermittent conditions, refer to Symptoms - Computers and Controls Systems. Symptom Related Diagnostic Procedures

Reviewing the Failure Records vehicle mileage since the diagnostic test last failed may assist in diagnosing the condition. The information may help determine how often the condition that set the DTC occurs.

TEST DESCRIPTION

Steps 1-9:

Steps 10-15:

The numbers below refer to the step numbers on the diagnostic table.
2. This step verifies whether or not the HO2S voltage is switching from below 300 mV to above 600 mV, or is remaining below 300 mV.
4. This step verifies the bias voltage from the PCM and the condition of the circuit wiring. With the sensor disconnected, the scan tool should display a bias voltage near 450 mV.