Circuit Description
A three-way catalytic converter controls emissions of hydrocarbons (HC), carbon monoxide (CO), and oxides of nitrogen (NOx). 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 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 that is present in the exhaust gas that enters 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 ability of the catalyst to efficiently convert the exhaust gases. If the catalyst is operating efficiently, the HO2S 1 signal will be far more active than the signal 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
| • | No TP sensor, EVAP system, misfire, IAT sensor, MAP sensor, fuel trim, fuel injector circuit, EGR Pintle Position, ECT sensor, CKP sensor, or MAF sensor DTCs are present. |
| • | The closed loop commanded air-to-fuel ratio is between 14:5 and 14:8. |
| • | The throttle angle is between 3 percent and 40 percent. |
Conditions for Setting the DTC
| • | HO2S 2 signal voltage remains below 10 mV during normal closed loop operation. |
| OR |
| • | HO2S 2 signal voltage remains below 600 mV during power enrichment mode fuel control operation. |
| • | VIN K--The condition is present for as long as 4 minutes. |
| • | VIN 1--The condition is present for as long as 2.5 minutes. |
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 OFF the malfunction indicator lamp (MIL) during the third consecutive trip in which the diagnostic has 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 conditions:
| • | 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 Wiring Systems . |
| • | Fuel pressure--A condition which causes a lean exhaust can cause the system to become lean if the fuel pressure is too low. The PCM can compensate for some decrease. However, if fuel pressure is too low, DTC P0137 will set. |
| • | 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--Refer to Crankcase Ventilation System Inspection . |
| - | Vacuum leaks at the throttle body, the GR valve, and the intake manifold mounting surfaces. |
| • | Exhaust leaks--An exhaust leak may cause 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. |
| • | The MAF sensor--Disconnect the MAF sensor and see if the condition is corrected. If so, replace MAF sensor. Refer to Mass Airflow Sensor Replacement . |
| • | Fuel contamination--Even small amounts of water 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 . |
Many situations may lead to an intermittent condition. Perform each inspection or test as directed.
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.
| • | Loose terminal connection |
| - | Use a corresponding mating terminal to test for proper tension. Refer to Testing for Intermittent Conditions and Poor Connections , and to Connector Repairs in Wiring Systems for diagnosis and repair. |
| - | Inspect the harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and faulty terminal to wire connection. Refer to Testing for Intermittent Conditions and Poor Connections , and to Connector Repairs in Wiring Systems for diagnosis and repair. |
| • | Damaged harness--Inspect the wiring harness for damage. If the harness inspection does not reveal a problem, observe the display on the scan tool while moving connectors and wiring harnesses related to the sensor. A change in the scan tool display may indicate the location of the fault. Refer to Wiring Repairs in Wiring Systems for diagnosis and repair. |
| • | Inspect the powertrain control module (PCM) and the engine grounds for clean and secure connections. Refer to Wiring Repairs in Wiring Systems for diagnosis and repair. |
If the condition is determined to be intermittent, reviewing the Snapshot or Freeze Frame/Failure Records may be useful in determining when the DTC or condition was identified.
Test Description
The numbers below refer to the step numbers on the diagnostic table:
-
DTC P0137 failing during power enrichment operation, when the TP angle is above 60 percent, may indicate a condition described in Diagnostic Aids.
-
When the PCM is replaced, you must program the new PCM.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
1 | Did you perform the Powertrain On Board Diagnostic (OBD) System Check? | -- | ||
2 |
Important: During this step, observe all H02S voltage parameters. If all parameters remain below the specified value, refer to Diagnostic Aids.
Is the voltage less than the specified value? | 10 mV | ||
Does the DTC reset? | -- | Go to Diagnostic Aids | ||
4 | Disconnect the HO2S 2 and jumper the low circuit on the PCM side to ground. Does the voltage measure near the specified value? | 450 mV | Go to Diagnostic Aids | |
5 | Turn OFF the ignition, disconnect the PCM, and test the HO2S 2 signal circuit for a short to ground, or for a short to the sensor ground circuit. Did you find a condition? | -- | ||
6 | Repair the HO2S 2 signal circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | -- | |
|
Important: You must program the replacement PCM. Replace the PCM. Refer to Powertrain Control Module Replacement/Programming . Did you complete the replacement? | -- | -- | ||
8 |
Does the DTC reset? | -- | System OK |
