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 of the exhaust stream. When the vehicle is first started, the powertrain control module (PCM) operates in an Open Loop mode, ignoring the HO2S signal voltage when calculating the air-to-fuel ratio. The PCM supplies the HO2S with a reference, or bias, voltage of 450 mV. The HO2S generates a voltage within a range of 0-1000 mV, that fluctuates above and below bias voltage once in Closed Loop. A high HO2S voltage output indicates a rich fuel mixture. A low HO2S voltage output indicates a lean mixture. A heating element inside the HO2S reduces the time required for the sensor to reach operating temperature, and provide an accurate voltage signal.

This DTC will set if the HO2S voltage is more than a calibrated amount for an excessive amount of time.

### Conditions for Running the DTC

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

• | The engine coolant temperature (ECT) is more than 70°C (158°F).

• | The battery voltage is more than 10 volts.

• | The fuel level is more than 10 percent.

• | The engine run time is more than 10 seconds.

• | The engine is operating in Closed Loop.

• | The throttle position (TP) angle is between 8-50 percent for 3.8 seconds.

• | The manifold absolute pressure (MAP) is more than 20 kPa.

### Conditions For Setting The DTC

HO2S 2 voltage is more than 1,042 mV for 50-75 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 numbers below refer to the step numbers on the diagnostic table.

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

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

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 |

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

Does the scan tool indicate that the HO2S 2 voltage is more than the specified value?

994 mV

Go to Step 4

Go to Step 3

3 |

1. Observe the Freeze Frame/Failure Records data 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 as specified in the supporting test, or as close to the Freeze Frame/Failure Records data that you observed.

Does the scan tool indicate that this DTC failed 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. Using a DMM, measure the voltage of the HO2S 2 high signal circuit on the PCM side.

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 voltage. 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 is detecting a rich exhaust condition or may be contaminated. Check for one of the following conditions:

• | HO2S connector water intrusion

• | A silicon-contaminated HO2S 2

• | Fuel-contaminated engine oil

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

• | A leaking fuel pressure regulator

• | Rich fuel injectors--Refer to Fuel System Diagnosis .

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. 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 | Important: Before replacing a contaminated HO2S, determine and repair the cause of the contamination. Replace the HO2S 2. Refer to Heated Oxygen Sensor 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. Use a 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 12

Go to Step 2

12 | 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