For 1990-2009 cars

### 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.

• | Clear the MIL and the DTC with a scan tool.

### 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 Wiring Systems.

• | 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 Solenoid Coil Test .

• | 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 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 .

### Test Description

The number below refers to the step number on the diagnostic table.

1. DTC P0137 failing during power enrichment operation, with the TP angle above 60 percent, may indicate a condition described in Diagnostic Aids.

Step | Action | Values | Yes | No
--- | --- | --- | --- | ---
Schematic Reference: Engine Controls Schematics
1 | Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | Go to Diagnostic System Check - Engine Controls
2 | Important: During this step, observe the HO2S voltage parameters. If all parameters remain below the specified value, refer to Diagnostic Aids.

1. Engine at operating temperature, operate the vehicle within Conditions For Setting the DTC as specified in the supporting text.
2. Monitor HO2S 2 voltage with a scan tool.

Does the voltage measure less than the specified value?

30 mV

Go to Step 4

Go to Step 3

3 |

1. Turn ON the ignition, with the engine OFF.
2. Review and record scan tool Failure Records data.
3. Operate vehicle within Failure Records conditions as noted.
4. With a scan tool, observe Specific DTC info for DTC P0137 until the DTC P0137 test runs.
5. Note the test result.

Does the DTC reset?

--

Go to Step 4

Go to Diagnostic Aids

4 | Disconnect HO2S 2 and jumper the HO2S low signal circuit (PCM side) to ground. Does the voltage measure near the specified value? | 450 mV | Go to Step 8 | Go to Step 5
5 |

1. Turn OFF the ignition.
2. Disconnect the PCM.
3. Test the HO2S 2 high signal circuit for a short to ground or a short to the HO2S low signal circuit.

Did you find the condition?

--

Go to Step 6

Go to Step 7

6 | Repair the HO2S 2 high signal circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 9 | --
7 | Replace the PCM. Refer to Powertrain Control Module Replacement . Did you complete the replacement? | -- | Go to Step 9 | --
8 | Replace the affected HO2S sensor. Refer to Heated Oxygen Sensor 1 Replacement or Heated Oxygen Sensor 2 Replacement . Did you complete the replacement? | -- | Go to Step 9 | --
9 |

1. Use the scan tool in order to clear the DTCs.
2. Turn OFF the ignition for 30 seconds.
3. Start the engine.
4. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC run and pass?

--

Go to Step 10

Go to Step 2

10 | With a scan tool, observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | -- | Go to Diagnostic Trouble Code (DTC) List | System OK