P0137

Schematic:

CIRCUIT DESCRIPTION
To control emissions of Hydrocarbons (HC), Carbon Monoxide (CO), and Oxides of Nitrogen (NOx), a three-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 PCM has the ability to monitor this process using the post-catalyst HO2S. This HO2S 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 post HO2S signal voltage remains excessively low for an extended period of time, this DTC will set.

CONDITIONS FOR RUNNING THE DTC
^ No Misfire, Transmission, Fuel injector, MAF, TP, EVAP, IAT, MAP, Fuel trim, EGR or ECT DTCs are present.
^ Closed loop commanded air/fuel ratio is between 14.5 - 14.8.
^ Throttle angle is between 5 percent and 40 percent.
^ The engine coolant temperature is more than 75°C (165°F).

CONDITIONS FOR SETTING THE DTC
Post HO2S signal voltage remains less than 60 mV during normal closed loop operation.
OR
Post HO2S signal voltage remains less than 600 mV during power enrichment mode.

ACTION TAKEN WHEN THE DTC SETS
^ The PCM will illuminate the Malfunction Indicator Lamp (MIL) during the second consecutive trip in which the diagnostic test has been run and failed.
^ The PCM will store conditions which were present when the DTC set as Freeze Frame/Failure Records data.

CONDITIONS FOR CLEARING THE MIL/DTC
^ The PCM will turn the MIL OFF during the third consecutive trip in which the diagnostic has been run and passed.
^ The History DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.
^ The DTC can be cleared by using a scan tool.

DIAGNOSTIC AIDS
Inspect for the following:
^ Fuel pressure low - A condition which causes a lean exhaust can cause this DTC to set. The system will go lean it pressure is too low. The PCM can compensate for some decrease. However, if fuel pressure is too low, this DTC may set. Refer to Fuel System Pressure Test. Fuel System Pressure Test
^ Fuel injectors faulty - Refer to Fuel Injector Balance Test Component Tests and General Diagnostics
^ Vacuum leaks - Inspect for a disconnected or damaged vacuum hoses and for vacuum leaks at the intake manifold, throttle body, EGR system, and crankcase ventilation system.
^ Exhaust leaks - An exhaust leak may cause outside air to be pulled into the exhaust gas stream past the HO2S, causing this DTC to set. Inspect for exhaust leaks near the oxygen sensors.
^ MAF sensor faulty - Disconnect the MAF sensor and see if the condition is corrected. If so, replace MAF sensor.
^ 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. Testing and Inspection

IMPORTANT: Remove any debris from the connector surfaces before servicing a component. Inspect the connector gaskets when diagnosing or replacing a component. Ensure that the gaskets are installed correctly. The gaskets prevent contaminate intrusion.

^ Poor terminal connection.
Inspect the harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and faulty terminal to wire connection. Use a corresponding mating terminal to test for proper tension. Refer to Testing for Intermittent and Poor Connections and Connector Repairs in Diagrams.
^ Damaged harness.
Inspect the wiring harness for damage. If the harness appears to be OK, observe the display on the scan tool while moving connectors and wiring harnesses related to the sensor. A change in the display may indicate the location of the fault. Refer to Wiring Repairs in Diagrams.
^ Inspect the PCM and the engine grounds for clean and secure connections.

If the DTC is determined to be intermittent, reviewing the Failure Records can be useful in determining when the DTC was last set.

TEST DESCRIPTION

Diagnostic Chart:

The numbers below refer to the step numbers on the diagnostic table:
3. This DTC setting during power enrichment mode conditions may indicate a condition described in the Diagnostic Aids above. If this DTC test passes while the Fail Records conditions are being duplicated, an intermittent condition is indicated. Review the Fail Records vehicle mileage since the diagnostic test last failed. This may help determine how often the condition that caused the DTC to be set occurs.
7. This vehicle is equipped with a PCM which utilizes an Electrically Erasable Programmable Read Only Memory (EEPROM). When the PCM is replaced, the new PCM must be programmed.