For 1990-2009 cars

### Circuit Description

The DTC P0137 Heated Oxygen Sensor (HO2S) Circuit Low Voltage Sensor 2 diagnostic monitors the output of the post catalyst HO2S. The powertrain control module (PCM) has the ability to determine the efficiency of the three-way catalytic (TWC) converter using the HO2S 1 and the HO2S 2. The HO2S produces a voltage between 100 mV and 900 mV that varies depending upon the oxygen content of the exhaust stream. The HO2S 1 output signal indicates the amount of oxygen present in the exhaust gases entering the TWC converter. The HO2S 2 output signal indicates the oxygen storage capacity of the catalyst in the TWC converter. The oxygen storage capacity of the catalyst is an indicator of the effectiveness of the TWC converter. The HO2S 1 output signal is more active than the HO2S 2 output signal when the catalyst is operating efficiently. If the HO2S 2 voltage remains excessively low or high for an extended period of time, a DTC P0137 will set.

### Conditions for Running the DTC

• | Barometric pressure (BARO) is more than 75 kPa.

• | Engine coolant temperature (ECT) is between -8°C and +110°C (18-230°F).

• | Intake air temperature (IAT) is more than -8°C (18°F) at engine start up.

• | Vehicle speed between 50-60 km/h (30-40 mph) for 3 minutes with throttle position constant.

### Conditions for Setting the DTC

The PCM detects a signal voltage that hovers at an extreme high or low voltage.

### Action Taken When the DTC Sets

• | The PCM illuminates the malfunction indicator lamp (MIL) after 2 consecutive ignition cycles in which the diagnostic runs with the fault.

• | The PCM records the operating conditions at the time the diagnostic fails. This information will be stored in the Freeze Frame buffer.

### Conditions for Clearing the MIL/DTC

• | The PCM tuns OFF the MIL after 3 consecutive trips without a fault.

• | The PCM clears a history DTC after 40 consecutive warm-up cycles without a fault.

• | Perform the scan tool clear DTC Information function in order to clear the DTC.

### Diagnostic Aids

A DTC P0137 is more likely to set during city driving. Avoid operating the vehicle on the highway when validating a DTC P0137.

If a DTC P0137 is intermittent, driving the vehicle under the conditions outlined in the Inspection/Maintenance (I/M) section can verify whether the fault is present. Refer to Inspection/Maintenance Heated Oxygen Sensor/Oxygen Sensor System Set .

An intermittent malfunction may be caused by a fault in the HO2S sensor circuit. Inspect the wiring harness and components for an intermittent condition. Refer to Intermittent Conditions .

If the DTC P0137 cannot be duplicated, the information included in the Freeze Frame data can be useful in determining vehicle operating conditions when the DTC first set.

### Test Description

The numbers below refer to the step numbers in the diagnostic table.

1. The Diagnostic System Check-Engine Controls prompts the technician to complete some basic checks and store the Freeze Frame data on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. The information is then stored in the scan tool for later reference.

2. This step provides a quick check of the HO2S operation. The vehicle must be at operating temperature.

3. This step checks whether the malfunction that caused the DTC is still present. After performing the scan tool clear DTC information function, monitor DTC P0137 on the scan tool under the Not Ran Since Code Cleared selection in the DTC Information menu. If a DTC P0137 appears in the Not Ran Since Code Cleared list, the diagnostic has not yet run. When the DTC does not appear in the Not Ran Since Code Cleared list, the diagnostic has run.

4. This step checks for a short to voltage on the HO2S 2 signal circuit.

5. This step checks for an open in the HO2S 2 ground circuit.

6. This step checks the HO2S 2 signal circuit. The DMM is used as a low current voltage source, taking the place of the HO2S. This tests the continuity of the signal wire , and if the PCM is able to receive and process a signal from the HO2S.

7. A possible cause of a voltage short to the HO2S 2 signal circuit is water. Check the wiring harness and PCM connectors for water that may cause ignition positive voltage to be shorted to the signal circuit.

8. Clearing the DTCs by removing the DOME fuse also clears the PCM long term memory. Using the scan tool to clear DTCs leaves the long term memory active. DTC emitting diagnostics may not run to completion as expected unless the long term memory is cleared. Removal of the DOME fuse also clears the time display of the radio. The DTC P0137 diagnostic can be monitored on the scan tool under the Not Ran Since Code Cleared selection in the DTC Information menu. If a DTC P0137 appears in the Not Ran Since Code Cleared list, the DTC P0137 diagnostic has not yet run. When the DTC P0137 does not appear in the Not Ran Since Code Cleared list, the DTC P0137 diagnostic has run. If the MIL is NOT illuminated, and there is no Pending DTC Status in DTC Information, the DTC P0137 diagnostic has passed. The DTCs MUST be cleared in order to view the Current Status of the Not Ran Since Code Cleared list. The Not Ran Since Code Cleared list only indicates whether or not the test has run, not whether the test passed or failed. The DTC Information screen must be checked for Current or Pending status, in order to determine the outcome of the diagnostic test involved.

Step | Action | Value(s) | 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 | Are any HO2S DTCs set other than DTC P0137 and DTC P0138? | -- | Go to Diagnostic Trouble Code (DTC) List | Go to Step 3
3 |

1. Start the engine.
2. Run the engine until the engine reaches a normal operating temperature.
3. Increase the engine speed to 2,000 RPM for 1 minute.
4. Monitor the applicable HO2S voltage with a scan tool.

Does the HO2S voltage switch below and above the specified range?

300-600 mV

Go to Step 4

Go to Step 5

4 |

1. Turn ON the ignition, leaving the engine OFF.
2. Perform the scan tool clear DTC information function.
3. Operate the vehicle within Freeze Frame conditions as specified or until the applicable DTC diagnostic test has run. Refer to the Test Description.
4. Monitor the HO2S 2 voltage while operating the vehicle.

Does the HO2S voltage switch below and above the specified range?

300-600 mV

Go to Diagnostic Aids

Go to Step 5

5 |

1. Turn OFF the ignition.
2. Disconnect the electrical connector of the suspect HO2S.
3. Disconnect the C2 electrical connector of the PCM.
4. Turn ON the ignition, leaving the engine OFF.
5. Connect a DMM from ground to the oxygen sensor signal circuit on the harness side of the electrical connector.

Is the voltage at the specified value?

0.0 V

Go to Step 6

Go to Step 10

6 |

1. Turn OFF the ignition.
2. Connect the PCM C2 electrical connector.
3. Turn ON the ignition, with the engine OFF.
4. Probe the HO2S ground circuit at the HO2S connector with a test lamp connected to B+.

Does the test lamp illuminate?

--

Go to Step 7

Go to Step 8

7 |

1. Use the DMM and select the Millivolt DC scale.
2. Connect one lead of the DMM to B+.
3. Connect the other lead of the DMM to the signal circuit of the suspect HO2S.
4. Start the engine.
5. Observe the HO2S voltage parameter on the scan tool.

Is the voltage at the specified value?

1,000 mV

Go to Step 11

Go to Step 9

8 |

1. Check for an open in the ground circuit of the HO2S.
2. Repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 13

Go to Step 12

9 |

1. Check the HO2S signal circuit for the following conditions:

• | Open Circuit

• | Short to ground

• | High circuit resistance

2. Repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 13

Go to Step 12

10 | Repair the short to voltage in the HO2S signal circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 13 | --
11 | Replace the faulty HO2S. Refer to Heated Oxygen Sensor 2 Replacement . Did you complete the replacement? | -- | Go to Step 13 | --
12 | Important: The replacement PCM must be programmed. Replace the PCM. Refer to Powertrain Control Module Replacement . Did you complete the replacement? | -- | Go to Step 13 | --
13 |

1. Turn OFF the ignition.
2. Remove the DOME fuse for 30 seconds.
3. Install the DOME fuse.
4. Reset the radio clock time. Refer to Radio/Audio System Description and Operation in Entertainment.
5. Start the engine.
6. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text or until the DTC P0137 diagnostic test has run.

Does the DTC run and pass?

--

Go to Step 14

Go to Step 2

14 | 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