Circuit Description
In order to control the 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 that are present in the exhaust gas, converting these chemicals into harmless water vapor and carbon dioxide. The catalyst also reduces the NOx, converting it to nitrogen. The powertrain control module (PCM) can monitor this process using the heated oxygyn sensors (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 the exhaust gases efficiently. If the catalyst is operating efficiently, the HO2S 1 signal will be far more active than the signal that is produced by the HO2S 2 sensor. If the HO2S 2 high signal voltage remains excessively low for an extended time, DTC P0137 will be set.
Conditions for Running the DTC
| • | DTCs P0101, P0102, P0103, P0107, P0108, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0125, P0128, P0201, P0202, P0203, P0204, P0205, P0206, P0410, P0440, P0442, P0443, P0446, P0449, or P1441 are not set. |
| • | The closed loop commanded air/fuel ratio is between 14.5-14.8. |
| • | The throttle angle is between 3-40 percent. |
Conditions for Setting the DTC
| • | 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 |
| • | The condition is present for up to 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. |
| • | Clear the MIL and the DTC with a scan tool. |
Diagnostic Aids
| • | Inspect the following components and 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 . |
| - | The fuel pressure--A condition that causes a lean exhaust can cause DTC P0137 to set. The system will go lean if pressure is too low. The PCM can compensate for some decrease. If fuel pressure is too low, a DTC P0137 may be set. |
| - | The fuel injectors--Refer to Fuel Injector Solenoid Coil Test . |
| - | Vacuum leaks--Inspect for the following conditions: |
| • | Disconnected or damaged vacuum hoses-- Refer to Emission Hose Routing Diagram . |
| • | An 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 the DTC P0137 to set. Check for exhaust leaks near the HO2S 2 sensor. |
| - | The mass air flow (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--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 . |
| • | If none of the above conditions are present, replace the affected HO2S. Refer to Heated Oxygen Sensor 1 Replacement , or to Heated Oxygen Sensor 2 Replacement . |
Test Description
The number below refers to the step number on the diagnostic table:
Step | Action | Values | Yes | No |
|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics | ||||
1 | Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | |
2 |
Important: During this step, observe all H02S voltage parameters. If all the parameters remain below the specified value, refer to Diagnostic Aids.
Does the HO2S 2 voltage remain at less than the specified value? | 10 mV | Go to Step 4 | Go to Step 3 |
Does the scan tool indicate DTC P0137 failed this ignition? | -- | Go to Step 4 | Go to Diagnostic Aids | |
4 | Disconnect HO2S 2 and jumper the HO2S 2 low signal circuit on the PCM side to ground. Does the scan tool indicate HO2S 2 voltage near the specified value? | 450 mV | Go to Diagnostic Aids | Go to Step 5 |
5 |
Did you find and correct the condition? | -- | Go to Step 7 | Go to Step 6 |
6 | Replace the PCM. Refer to Powertrain Control Module Replacement . Did you complete the replacement? | -- | Go to Step 7 | -- |
7 |
Does the DTC run and pass? | -- | Go to Step 8 | Go to Step 2 |
8 | With a scan tool, observe the stored information in Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | -- | System OK | |
