For 1990-2009 cars

### Circuit Description

Heated oxygen sensors (HO2S) are used for fuel control and post catalyst monitoring. Each HO2S compares the oxygen content of the surrounding air with the oxygen content in the exhaust stream. The HO2S must reach operating temperature to provide an accurate voltage signal. Heating elements inside the HO2S minimize the time required for the sensors to reach operating temperature. The powertrain control module (PCM) supplies the HO2S with a reference, or bias, voltage of about 450 mV. When the engine is first started the PCM operates in open loop, ignoring the HO2S voltage signal. Once the HO2S reaches operating temperatures and Closed Loop is achieved, the HO2S generates a voltage within a range of 0-1,000 mV that fluctuates above and below bias voltage. High HO2S voltage indicates a rich exhaust stream. Low HO2S voltage indicates a lean exhaust stream.

If the PCM detects an HO2S voltage that stays below a specified value, DTC P1137 will set.

### Conditions for Running the DTC

• | DTCs P0105, P0107, P0108, P0112, P0113, P0117, P0118, P0122, P0123, P0125, P0128, P0201-P0204, P0300, P0301-P0304, P0336, P0410, P0440, P0442, P0446, P0452, P0453, P0506, P0507, P0601, P0602, P1441, or P1621 are not set.

• | The ECT Sensor parameter is more than 70°C (158°F).

• | The Power Enrichment parameter is active.

• | The Ignition 1 Signal parameter is more than 10 volts.

• | The Loop Status parameter is closed.

• | The Fuel Level Sensor parameter is more than 10 percent.

• | The Engine Run Time parameter is more than 10 seconds.

• | The above conditions are met for 5 seconds.

### Conditions for Setting the DTC

The PCM detects that the HO2S 1 parameter is more than 700 mV and the HO2S 2 parameter is less than 399 mV for 9.5 seconds.

### 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.

### Test Description

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

1. When the system is operating correctly, the HO2S 2 voltage should toggle above and below the bias voltage.

Step | Action | Values | Yes | No
--- | --- | --- | --- | ---
Schematic Reference: Engine Controls Schematics Connector End View Reference: Powertrain Control Module Connector End Views or Engine Controls Connector End Views
1 | Did you perform the Diagnostic System Check--Engine Controls? | -- | Go to Step 2 | Go to Diagnostic System Check - Engine Controls
2 |

1. Operate the engine at normal operating temperature.
2. Operate the engine above 1,200 RPM for 2 minutes.
3. Observe the HO2S 2 voltage parameter with the scan tool.

Does the scan tool indicate that the heated oxygen sensor (HO2S) 2 voltage is less than the specified value?

399 mV

Go to Step 4

Go to Step 3

3 |

1. Observe the Freeze Frame/Failure Records for this DTC.
2. Turn OFF the ignition for 30 seconds.
3. Start the engine.
4. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.

Did the DTC fail this ignition?

--

Go to Step 4

Go to Intermittent Conditions

4 |

1. Turn OFF the ignition.
2. Disconnect the HO2S 2 sensor.
3. Turn ON the ignition, with the engine OFF.
4. Measure the voltage of the HO2S 2 high signal circuit on the powertrain control module (PCM) side with the DMM.

Does the voltage measure within the specified value?

350-550 mV

Go to Step 6

Go to Step 5

5 | Test the HO2S 2 high signal circuit for a short to ground or a short to the low signal circuit. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 11 | Go to Step 8
6 | The HO2S 2 may be detecting a lean exhaust condition. Inspect for one of the following conditions:

• | HO2S connector water intrusion

• | An exhaust leak between the HO2S 2 and the engine--Refer to Exhaust Leakage in Engine Exhaust.

• | Vacuum leaks

• | Incorrect fuel pressure--Refer to Fuel System Diagnosis .

• | Lean fuel injectors--Refer to Fuel Injector Balance Test with Tech 2 .

Repair any of the above or similar engine conditions as necessary.

Did you find and correct the condition?

--

Go to Step 11

Go to Step 7

7 | Inspect for poor connections at the harness connector of the HO2S 2 sensor. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 11 | Go to Step 9
8 | Inspect for poor connections at the harness connector of the PCM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 11 | Go to Step 10
9 | Replace the HO2S 2. Refer to Heated Oxygen Sensor 2 Replacement . Did you complete the replacement? | -- | Go to Step 11 | --
10 | Replace the PCM. Refer to Powertrain Control Module Replacement . Did you complete the replacement? | -- | Go to Step 11 | --
11 |

1. Clear the DTCs with a scan tool.
2. Turn OFF the ignition for 30 seconds.
3. Start the engine.
4. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.

Did the DTC fail this ignition?

--

Go to Step 2

Go to Step 12

12 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | -- | Go to Diagnostic Trouble Code (DTC) List | System OK