P0137

CIRCUIT DESCRIPTION
To control emissions of Hydrocarbons (HC), Carbon Monoxide (CO), and Oxides Of Nitrogen (NOx), a 3-way catalytic converter is used. The catalyst within the converter promotes a chemical reaction which oxidizes the HC and CO present in the exhaust gas, converting them into harmless water vapor and carbon dioxide. The catalyst also reduces NOx, converting it to nitrogen. The Powertrain Control Module (PCM) has the ability to monitor this process using the Heated Oxygen Sensor (HO2S 1) and the HO2S 2 heated oxygen sensors. The HO2S 1 sensor produces an output signal which indicates the amount of oxygen present in the exhaust gas entering the three-way catalytic converter. The HO2S 2 sensor produces an output signal which indicates the oxygen storage capacity of the catalyst. This in turn indicates the catalysts ability to convert exhaust gases efficiently. If the catalyst is operating efficiently, the HO2S 1 signal will be far more active than that produced by the HO2S 2 sensor. If the HO2S 2 signal voltage remains excessively low for an extended time, DTC P0137 will set.

CONDITIONS FOR RUNNING THE DTC
^ DTCs P0101, P0102, P0103, P0107, P0108, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0125, P0128, P0201-P0206, P0410, P0440, P0442, P0443, P0446, P0449, or P1441 are not set.
^ The Closed Loop commanded air/fuel ratio is between 12-16.5.
^ The throttle angle is between 3-40 percent.

CONDITIONS FOR SETTING THE DTC
^ HO2S 2 signal voltage remains less than 30 mV during normal Closed Loop operation.

OR

^ HO2S 2 signal voltage remains below 550 mV during power enrichment mode fuel control operation.
^ The condition is present for up to 2.5 minutes.

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.
^ Use a scan tool in order to clear the MIL and the DTC.

DIAGNOSTIC AIDS
Inspect for the following conditions:
^ The heated oxygen sensor wiring-The sensor pigtail may be mis-positioned and contacting the exhaust system.
^ Poor PCM to engine grounds-Refer to Ground Distribution Schematics in Diagrams.
^ The fuel pressure-A condition which causes a lean exhaust. The system will go lean if pressure is too low. The PCM can compensate for some decrease. However, if fuel pressure is too low, DTC P0137 will set.
^ Lean injectors-Refer to Fuel Injector Coil Test. Component Tests and General Diagnostics
^ Vacuum leaks-Inspect for the following conditions:
- Disconnected or damaged vacuum hoses- Refer to Emission Hose Routing Diagram.
- Incorrectly installed or malfunctioning crankcase ventilation valve
- Vacuum leaks at the throttle body, the Exhaust Gas Recirculation (EGR) valve, and the intake manifold mounting surfaces
^ Exhaust leaks-An exhaust leak may cause the outside air to be pulled into the exhaust gas stream past the HO2S, causing DTC P0137 to set. Inspect for exhaust leaks near the HO2S 2 sensor.
^ The MAF sensor-Disconnect the MAF sensor and see if the condition is corrected. If so, replace the MAF sensor. Refer to Mass Air Flow (MAF) Sensor Replacement.
^ Fuel contamination-Water, even in small amounts, can be delivered to the fuel injectors. The water can cause a lean exhaust to be indicated. Excessive alcohol in the fuel can also cause this condition. Refer to Alcohol/Contaminants-in-Fuel Diagnosis (Without Special Tool) or Alcohol/Contaminants-in-Fuel Diagnosis (With Special Tool). Component Tests and General Diagnostics Component Tests and General Diagnostics

TEST DESCRIPTION

Steps 1-10:

The number below refers to the step number on the diagnostic table.
3. DTC P0137 failing during power enrichment operation, with the TP angle above 60 percent, may indicate a condition described in Diagnostic Aids.