For 1990-2009 cars
Engine Controls Components
Cell 20: HO2S
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice

### Circuit Description

The powertrain control module (PCM) continuously monitors the heated oxygen sensor (HO2S) activity. The PCM counts the number of times that the a rich to lean and lean to rich response is indicated and adds the amount of time it took to complete all the transitions. The PCM uses this information in order to determine an average time for each transition. A DTC P0133 will set if the average transition (response) time is too slow.

A lean to rich transition is indicated when the HO2S voltage changes from less than 300 mV to greater than 600 mV. A rich to lean transition is indicated when the HO2S voltage changes from more than 600 mV to less than 300 mV. An HO2S that responds too slowly may be faulty and should be replaced.

### Conditions for Running the DTC

• | Engine coolant temperature is greater than 70°C (158°F).

• | Engine is running at idle.

### Conditions for Setting the DTC

Response time necessary for the HO2S voltage to change from rich to lean, or lean to rich, is 1.1 seconds or more.

### Action Taken When the DTC Sets

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

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

### Conditions for Clearing the MIL/DTC

• | The MIL turns OFF after three consecutively passing trips without a fault present.

• | A History DTC clears after 40 consecutive warm-up cycles without a fault.

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

### Diagnostic Aids

Check for a contaminated HO2S. Silicon contamination of the HO2S can cause a low signal voltage to be indicated. Silicon contamination is indicated by a powdery white deposit on the portion of the HO2S exposed to the exhaust stream. Before replacing the HO2S determine the cause and correct the condition.

An intermittent malfunction may be caused by fault in the HO2S 1 electrical circuit. Inspect the wiring harness and components for any of the following conditions:

• | Backed out terminals.

• | Improper mating of terminals.

• | Broken electrical connectors locks.

• | Improperly formed or damaged terminals

• | Faulty terminal to wire connections.

• | Physical damage to the wiring harness.

• | A broken wire inside the insulation.

• | Corrosion of electrical connections, splices, or terminals.

Repair any electrical circuit faults that were found. Refer to Wiring Repairs .

The information included in the Freeze Frame data can be useful in determining the vehicle operating conditions when the DTC first set.

### Test Description

The numbers below refer to the step numbers in the Diagnostic Table.

1. The OBD System Check 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 checks whether the malfunction that caused the DTC P0133 is still present. Operating the vehicle in check mode enhances the PCM's diagnostic capabilities. The HO2S 1 diagnostic can be monitored on the scan tool under the MIL/System Status selection of System Information. When the HO2S test displays a YES status (indicating that the heated oxygen sensor system diagnostic is completed) check for a DTC P0133 in the Last Test Failed screen of the scan tool. If there is no DTC P0133 displayed the HO2S diagnostic has run and passed, indicating that no malfunction was present this time. DTCs MUST BE CLEARED in order to view the CURRENT STATUS of the system diagnostics being performed. Do not forget that the MIL/System Status tests only indicate that the test has run, not whether the test passed or failed. The Last Test Failed screen must be checked for related DTCs in order to determine the outcome of the diagnostic test involved. For additional information on check mode operation refer to Powertrain Control Module Diagnosis .

3. In this step the DMM is used as a low current voltage source taking the place of the HO2S. This step verifies whether the PCM is able to receive and process a signal from the HO2S 1.

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | Go to Step 2 | Go to Powertrain On Board Diagnostic (OBD) System Check
2 |

1. Perform the scan tool Clear DTC Information function.
2. Place the vehicle into Check Mode, using the scan tool.
3. Operate the vehicle within the Freeze Frame conditions as specified or until the HO2S test is complete. Refer to the Test Description.

Did a DTC P0133 set?

--

Go to Step 3

Fault Not Present-Go to Diagnostic Aids

3 |

1. Visually/physically inspect the following items:

1.1. | Ensure that the HO2S 1 is securely installed.

1.2. | Check for corrosion on terminals.

1.3. | Check terminal tension (at the HO2S 1 and at the PCM).

1.4. | Check for damaged wiring.

2. Repair as necessary.

Was a repair necessary?

--

Go to Step 11

Go to Step 4

4 |

1. Check the exhaust system for an exhaust leak near the engine.
2. Repair as necessary.

Was an exhaust leak found?

--

Go to Step 11

Go to Step 5

5 |

1. Disconnect the HO2S 1 connector.
2. Turn ON the ignition, leaving the engine OFF.
3. Select the J 39200 DMM to measure DC MILLIVOLTS.
4. Place the positive lead of the DMM on battery positive voltage, and the negative lead on the HO2S 1 sensor input circuit terminal (engine harness side).
5. Observe the HO2S 1 parameter on the scan tool.

Does the scan tool read greater than the specified value?

1155 mV

Go to Step 6

Go to Step 7

6 |

1. Connect a test lamp to battery voltage.
2. Probe the HO2S 1 sensor ground circuit terminal at the HO2S connector (engine harness side).

Does the test lamp illuminate?

--

Go to Step 9

Go to Step 8

7 |

1. Check for an open or short in the HO2S 1 input circuit between the HO2S 1 and the PCM connector.
2. Repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Was a repair necessary?

--

Go to Step 11

Go to Step 10

8 | Repair the open in the HO2S 1 ground circuit between the HO2S 1 and the G106. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | Go to Step 11 | --
9 | Important: Before installing the replacement sensor, the cause of possible contamination must be determined and corrected.

1. Check for and repair possible causes of HO2S contamination.

Possible causes include the following:

• | Fuel contamination.

• | Use of improper RTV sealant.

• | Engine oil/coolant consumption.

2. Repair as necessary.
3. Replace the HO2S 1. Refer to Heated Oxygen Sensor Replacement .

Is the action complete?

--

Go to Step 11

--

10 | Replace the PCM. Refer to Powertrain Control Module Replacement . Is the action complete? | -- | Go to Step 11 | --
11 |

1. Perform the scan tool Clear DTC Information function and road test the vehicle within the Freeze Frame conditions that set the DTC.
2. Review the scan tool data and check for DTCs. The repair is complete if no DTCs are stored.

Are any DTCs displayed on scan tool?

--

Go to the applicable DTC table

System OK