P0137

Diagnostic Chart:

Schematic:

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. If HO2S bank 1 sensor 2 remains too low for a calibrated period of time, DTC P0137 will set.

CONDITIONS FOR RUNNING THE DTC
^ No MAF, TP, EVAP, IAT, MAP, AIR (if equipped), ECT, or Injector DTCs set
^ EGR flow diagnostic test inactive
^ AIR (if equipped) diagnostic test inactive
^ Catalyst diagnostic test inactive
^ System voltage between 9-18 volts
^ Engine running more than 200 seconds
^ Change in TP angle more than 5 percent occurs at least 4 times

CONDITIONS FOR SETTING THE DTC
HO2S bank 1 sensor 2 signal voltage remains between 400 mV (0.4 volts) and 500 mV (0.5 volts) for approximately 57 seconds during normal closed loop fuel control.

ACTION TAKEN WHEN THE DTC SETS
^ The PCM illuminates the Malfunction Indicator Lamp (MIL) during the second consecutive trip in which the diagnostic test runs and fails.
^ The PCM stores the conditions present when the DTC set as Freeze Frame and Fail Records data.

CONDITIONS FOR CLEARING THE MIL/DTC
^ The PCM will turn the MIL OFF after the third consecutive trip in which the diagnostic runs and passes.
^ The history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.
^ The DTC can be cleared by using the scan tool Clear DTC Information function.

DIAGNOSTIC AIDS
If the condition is intermittent, refer to Intermittent Conditions in Symptoms. Intermittent Conditions

Exhaust leaks Exhaust leaks may cause outside air to be drawn into the exhaust gas stream, and pass the HO2S sensor. This causes the HO2S signal to indicate a false lean condition.

If none of the above conditions are present, replace HO2S bank 1 sensor 2.

TEST DESCRIPTION
The numbers below refer to the step numbers on the diagnostic table.
2. Verifies whether or not the HO2S sensor voltage is switching from below 300 mV to above 500 mV, or remaining below 300 mV.
4. 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.