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 the CO present in the exhaust gas, converting them into harmless water vapor and carbon dioxide. The catalyst also converts the NOx to nitrogen. The powertrain control module (PCM) has the ability to monitor this process using the 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 3-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 catalyst's ability to convert exhaust gases efficiently. If the catalyst is operating efficiently, the HO2S 1 signal is far more active than that produced by the HO2S 2 sensor. If the HO2S 2 signal voltage remains excessively low for an extended period of time, DTC P0137 is set.
Conditions for Setting the DTC
| • | None of the following DTCs are present: |
| - | Throttle position (TP) sensor DTCs |
| - | Evaporative emissions (EVAP) DTCs |
| - | Intake air temperature (IAT) sensor DTCs |
| - | Manifold absolute pressure (MAP) sensor DTCs |
| - | Exhaust gas recirculation (EGR) pintle position DTCs |
| - | Engine coolant temperature (ECT) sensor DTCs |
| - | Crankshaft position (CKP) sensor DTCs |
| - | Mass air flow (MAF) sensor DTCs |
| - | Misfire DTCs |
| - | Fuel trim DTCs |
| - | Fuel injector circuit DTCs |
| • | The closed loop commanded air/fuel ratio is between 14.5 and 14.8 |
| • | The throttle angle is between 3% and 40%. |
| • | The HO2S 2 signal voltage remains below 10 mV during normal closed loop operation. |
OR
| • | The HO2S 2 signal voltage remains below 600 mV during power enrichment mode fuel control operation |
| • | Either condition is present for up to 3 minutes. |
Action Taken When the DTC Sets
| • | The PCM illuminates the malfunction indicator lamp (MIL) during the second consecutive trip in which the diagnostic test has run and failed. |
| • | The PCM stores the conditions which were present when the DTC set as Freeze Frame and Fail Records data. |
Conditions for Clearing the MIL/DTC
| • | The PCM turns the MIL off during the third consecutive trip in which the diagnostic has run and passed. |
| • | The history DTC clears after 40 consecutive warm-up cycles have occurred without a malfunction. |
| • | The DTC may be cleared by using the scan tool Clear Info function or by disconnecting the PCM battery feed. |
Diagnostic Aids
Inspect for the following conditions:
| • | Inspect the heated oxygen sensor wiring. The sensor pigtail may be misrouted and contacting the exhaust system. |
| • | A faulty PCM to engine ground. Refer to Wiring Repairs in Electrical Diagnosis. |
| • | Test the fuel pressure. A condition which causes a lean exhaust may cause DTC P0137 to set. The system goes lean if the pressure is too low. The PCM may compensate for some decrease. However, if fuel pressure is too low a DTC P0137 may be set. |
| • | Inspect for vacuum leaks at the following locations: |
| - | Any disconnected or damaged vacuum hoses. |
| - | Refer to Emission Hose Routing Diagram . |
| - | An incorrectly installed or malfunctioning crankcase ventilation valve. |
| - | Inspect the throttle body, the EGR valve, and the intake manifold mounting surfaces. |
| • | Inspect for exhaust leaks. An exhaust leak may allow outside air to be pulled into the exhaust gas stream past the HO2S, causing the DTC P0137 to set. Inspect for exhaust leaks near the HO2S 2 sensor. |
| • | Disconnect the MAF sensor and note if the condition is corrected. If the condition is corrected by disconnecting the sensor, replace MAF sensor. Refer to Mass Airflow Sensor Replacement . |
| • | Test for fuel contamination. Water, even in small amounts, may be delivered to the fuel injectors. The water may cause a lean exhaust to be indicated. Excessive alcohol in the fuel may also cause this condition. Refer to Alcohol/Contaminants-in-Fuel Diagnosis . |
Test Description
The number(s) below refer to the step number(s) on the Diagnostic Table.
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DTC P0137 failing during power enrichment operation (TP angle above 60%) may indicate a condition described in Diagnostic Aids. If the DTC P0137 test passes while the Fail Records conditions are being duplicated, an intermittent condition is indicated. Reviewing the Fail Records vehicle mileage since the diagnostic test last failed may help determine how often the condition that caused the DTC to be set occurs. This may assist in diagnosing the condition.
-
This vehicle is equipped with a powertrain control module (PCM) which utilizes an electrically erasable programmable read-only memory (EEPROM). When the PCM is replaced, the new PCM must be programmed.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | ||
2 |
Does the HO2S 2 voltage remain at less than the specified value? | 10 mV | ||
Does the scan tool indicate DTC P0137 Failed This Ign? | -- | Go to Diagnostic Aids | ||
4 | Disconnect the HO2S 2 and jumper the HO2S 2 low circuit (PCM side) to ground. Is the HO2S 2 voltage near the specified value? | 450 mV | Go to Diagnostic Aids | |
5 |
Is the HO2S 2 signal circuit shorted? | -- | ||
6 | Repair the HO2S 2 signal circuit. Refer to Heated Oxygen Sensor Wiring Repairs . Did you complete the repair? | -- | -- | |
|
Important:: The replacement PCM must be programmed. Refer to Powertrain Control Module Replacement/Programming . Replace the PCM. Did you complete the repair? | -- | -- | ||
8 |
Does the scan tool indicate DTC P0137 Failed This Ign? | -- | System OK |
