For 1990-2009 cars
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. During the monitoring period the PCM counts the number of times that a rich-to-lean and lean-to-rich response is indicated. The PCM then combines these counts with the amount of time involved to complete the transitions. With this information, an average time for each transition can be determined. If the average response time is too slow, DTC P0133 will be set.

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

### Conditions for Running the DTC

• | The barometric pressure (BARO) is more than 75 kPa.

• | The engine coolant temperature (ECT) is between -8°C (+18°F) and +110°C (230°F).

• | The intake air temperature (IAT) is more than -8°C (+18°F) at engine start up.

• | The vehicle speed is more than 56 km/h (35 mph) for 2 minutes and then idled for 1 minute.

### Conditions for Setting the DTC

• | The average response rate is more than 2.5 second.

• | The switch cycle average is more than 6 seconds.

### Action Taken When the DTC Sets

• | The PCM illuminates the malfunction indicator lamp (MIL) after 2 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 3 consecutively passing trips without a fault present.

• | A history DTC will clear after 40 consecutive warm-up cycles without a fault.

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

### Diagnostic Aids

A DTC P0133 is more likely to set during city driving. Avoid operating the vehicle on the highway when validating a DTC P0131.

Check for any of the following conditions:

• | If any DTCs other than fuel trim (P0171, P0172), misfire (P0300 to P0304), EGR (P0400) and HO2S 1 (P0131 to P0134) are set, diagnosis those DTCs first.

• | A damaged wiring harness. Inspect the wiring harness for damage. If the harness appears to be OK, observe the HO2S 1 display on the scan tool while moving the connectors and the wiring harnesses related to the sensor. A change in the HO2S 1 display will indicate the location of the fault.

If a DTC P0133 is intermittent, driving the vehicle under the following conditions can verify whether the fault is present. Perform the scan tool clear DTC information function. Road test the vehicle while monitoring the DTC P0133 diagnostic on the scan tool under the Not Ran Since Code Cleared selection in the DTC Information menu. If a DTC P0133 appears in the Not Ran Since Code Cleared list, the P0133 diagnostic has not yet run. When the DTC P0133 does not appear in the Not Ran Since Code Cleared list, the P0133 diagnostic has run. If the MIL is NOT illuminated, and there is no Pending DTC Status in DTC Information, the P0133 diagnostic has passed. The DTCs MUST be cleared in order to view the Current Status of the Not Ran Since Code Cleared list. DO NOT forget that the Not Ran Since Code Cleared list only indicates that the test has run, not whether the test passed or failed. The DTC Information screen must be checked for Current or Pending status in order to determine the outcome of the diagnostic test involved.

An intermittent malfunction may be caused by a fault in the MAF sensor circuit. Inspect the wiring harness and components for any of the following conditions:

• | Any backed-out terminals

• | Any improper mating of terminals

• | Any broken electrical connector locks

• | Any improperly formed or damaged terminals

• | Any faulty terminal-to-wire connections

• | Any physical damage to the wiring harness

• | A broken wire inside the insulation

• | Any corrosion of the electrical connections, the splices, or the terminals

If the DTC P0133 cannot be duplicated, the information included in the Freeze Frame data can be useful in determining vehicle operating conditions when the DTC was 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 specified.

Does the scan tool indicate any DTCs other than DTC P0133?

--

Go to Diagnostic Trouble Code (DTC) List

Go to Step 3

3 | Visually and physically inspect for the following conditions:

• | The correct installation of the HO2S 1

• | Any corrosion of the electrical terminals

• | The correct 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 the exhaust leak 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 Diagnostic Trouble Code (DTC) List

System OK