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.

The DTC will set if the HO2S voltage activity remains at or near the bias voltage amount.

### 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 airflow is more than 3 grams per second (g/s).

• | The throttle position (TP) angle is between 8-56 percent.

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

• | The engine run time is more than 30 seconds.

### Conditions For Setting The DTC

The HO2S 1 voltage is between 399-499 mV for 125 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 1 voltage should toggle above and below the specified values.

2. The specified value is what is measured on a correctly operating system.

3. The specified value is what is measure on a correctly operating system.

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 1 voltage parameter.

Does the scan tool indicate that the HO2S 1 voltage is varying outside the specified values?

350-550 mV

Go to Step 3

Go to Step 4

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 text, 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 1.
3. Turn ON the ignition, with the engine OFF.
4. Using a DMM, measure the voltage of the HO2S 1 high signal circuit on the PCM side to a good ground.

Does the voltage measure within the specified value?

351-551 mV

Go to Step 5

Go to Step 7

5 |

1. Turn OFF the ignition.
2. Connect a 3-amp fused jumper wire between the HO2S 1 high signal circuit and the HO2S 1 low signal circuit.
3. Turn ON the ignition.
4. Use a scan tool in order to monitor the HO2S 1 voltage for the sensor that applies to this DTC.

Does the scan tool indicate that the HO2S 1 voltage is less than the specified value?

20 mV

Go to Step 8

Go to Step 6

6 | Test the HO2S 1 low signal circuit for an open, high resistance or short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 13 | Go to Step 10
7 | Test the HO2S 1 high signal circuit for the following conditions:

• | Open

• | High resistance

• | Short to voltage

Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 13

Go to Step 10

8 | Important: Before replacing the suspected HO2S, check and remove any source of contamination. Inspect for the following conditions:

• | The use of incorrect silicon RTV sealant

• | Fuel Contamination

• | Exhaust leak--Refer to Exhaust Leakage in Engine Exhaust.

• | The HO2S 1 is installed correctly.

• | Damaged wiring--Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 13

Go to Step 9

9 | Inspect for poor connections at the harness connector of the HO2S 1. 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 13 | Go to Step 11
10 | 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 13 | Go to Step 12
11 | Important: Determine the cause of contamination before replacing the sensor. Replace the HO2S 1. Refer to Heated Oxygen Sensor Replacement . Did you complete the replacement? | -- | Go to Step 13 | --
12 | Replace the PCM. Refer to Powertrain Control Module Replacement . Did you complete the replacement? | -- | Go to Step 13 | --
13 |

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 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