For 1990-2009 cars
Engine Controls Components
Cell 21: HO2S Sensors
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 transitions indicated, and adds the amount of time that is required to complete the transitions. The PCM uses this information in order to determine an average time for each transition. DTC P0133 sets if the average transition time is too slow.

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

### Conditions for Running the DTC

• | The barometric pressure is greater than 75 kPa.

• | The intake air temperature is between -10°C and +70°C (14°F - 158°F).

• | The fuel tank level is above 25 percent.

• | Engine coolant temperature is above 80°C (176°F).

• | The vehicle speed exceeds 50 km/h (30 mph) for 2 minutes, after which the vehicle is idled for 2 minutes.

• | The engine is running at a steady speed.

### Conditions for Setting the DTC

The response rate average is greater than 1 second.

OR

The switch cycle average is greater than 5 seconds.

### 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 that the diagnostic fails. This information is stored in the Freeze Frame buffer.

### Conditions for Clearing the DTC

• | The MIL turns OFF after 3 consecutive trips during which the diagnostic runs and does not detect a fault.

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

• | Use the Clear DTC Information function of the scan tool, or disconnect the PCM battery feed in order to clear the DTC.

### Diagnostic Aids

Before diagnosing Fuel Trim, Misfire, and HO2S 1 DTCs, diagnose any other DTCs .

A fault in the electrical circuit of the HO2S 1may cause an intermittent malfunction . Inspect the wiring harness and the components for any of the following conditions:

• | Backed out terminals

• | Incorrect mating of terminals

• | Broken electrical connector locks

• | Incorrectly formed terminals or damaged terminals

• | Faulty terminal-to-wire connections

• | Physical damage to the wiring harness

• | A broken wire inside the insulation

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

If DTC P0133 cannot be duplicated, 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 Powertrain 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 determines if the fault is present.

3. This step checks for an exhaust leak near the HO2S. Fresh air can enter the exhaust system through the exhaust leak and affect HO2S 1 performance.

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

1. Turn ON the ignition, leaving the engine OFF.
2. Use the scan tool clear information function.
3. Operate the vehicle within the Freeze Frame conditions as noted.

Does the scan tool indicate any DTCs besides a DTC P0133?

--

Go to the Applicable DTC Table

Go to Step 3

3 | Visually and physically inspect for the following conditions:

• | Proper installation of the HO2S 1.

• | Corrosion of the electrical terminals.

• | Proper tension of the electrical terminal connections at the HO2S 1 and at the PCM.

• | A damaged wiring harness.

• | A contaminated sensor.

Was a problem found in any of the above areas?

--

Go to Step 6

Go to Step 4

4 | Check the exhaust system for an exhaust leak near the engine. Was an exhaust leak found? | -- | Go to Step 6 | Go to Step 5
5 | Important: Inspect the oxygen sensor for contamination before replacing the sensor. Do not replace a contaminated oxygen sensor until the cause of the contamination is found and corrected. Replace the HO2S 1. Refer to Heated Oxygen Sensor Replacement .

Is the action complete?

--

Go to Step 7

--

6 | Repair exhaust condition as necessary. Is the action complete? | -- | Go to Step 7 | --
7 |

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 the scan tool?

--

Go to the Applicable DTC Table

System OK