P0133

Circuit Description
The PCM continuously monitors the Heated Oxygen Sensor (HO2S) activity for 100 seconds. During the monitoring period the PCM averages the amount of time of rich to lean and lean to rich transitions. With this information, an average time for each transition can be determined. If the average response time is too slow, a DTC P0133 will be set.

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 is likely to be faulty and should be replaced.

Conditions for Setting the DTC
^ No active misfire, fuel injector circuit, TP sensor, EVAP, IAT sensor, MAP sensor, Fuel trim, EGR, ECT sensor, MAF sensor or CKP sensor DTCs present.
^ Engine has been running in Closed Loop for at least 1 minute.
^ Engine speed is between 1000 RPM and 3000 RPM.
^ Engine Coolant Temperature greater than 50°C (122°F).
^ Mass Air Flow between 10 gm/s and 30 gm/s.
^ HO2S 1 lean to rich average transition response time was longer than 153 milliseconds.
^ HO2S 1 rich to lean average transition response time was longer than 148 milliseconds.

Action Taken When the DTC Sets
^ The PCM will illuminate the Malfunction Indicator Lamp (MIL) during the second consecutive trip in which the diagnostic test has been run and failed.
^ The PCM will store conditions which were present when the DTC set as Freeze Frame and Failure Records data.

Conditions for Clearing the MIL/DTC
^ The PCM will turn the MIL OFF during the third consecutive trip in which the diagnostic has been run and passed.
^ The history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.
^ The DTC can be cleared by using the scan tool.

Diagnostic Aids
Check for the following conditions:
^ Poor connection at PCM. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal to wire connection. Refer to Intermittents and Poor Connections.
^ Damaged 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 connectors and wiring harnesses related to the sensor. A change in the display will indicate the location of the fault.
^ Check for HO2S contamination. Refer to notice Silicon Contamination of Heated Oxygen Sensors Notice. Symptom Related Diagnostic Procedures

If DTC P0133 cannot be duplicated, Reviewing the Fail Records vehicle mileage since the diagnostic test last failed may help determine how often the condition that caused the DTC to be set occurs. This may assist in diagnosing the condition.

Test Description
The numbers below refer to the step numbers on the Diagnostic Table:
2. Verifies that the fault is currently present.
3. HO2S transition time, ratio, and switching DTCs set for multiple sensors indicate probable contamination. Before replacing the sensors, isolate and correct the source of the contamination to avoid damaging the replacement sensors.