DTC P0133 HO2S Heated Oxygen Sensor Slow Response

This Diagnostic Trouble Code (DTC P0133) relates to the Oxygen Sensor (HO2S) sometimes referred to as an Airflow Sensor in the Bank 1 Sensor 1 position. This location is pre-catalyst and typically on the right bank of a v6 or v8 engine or near the front of a dual banked 4 cylinder (eg: Rav4).  This stored Diagnostic Trouble Code (DTC P0133) is not definitive enough to just replace the part based upon its’ indication

This DTC P0133 indicates that the Powertrain Control Module (PCM) has monitored the sensor and found that its’ switching times (lean to rich or rich to lean) are too slow.

Oxygen Sensors (1, 3 and 4 wires) generally have output sensor voltages that oscillate between 2/10 and 8/10 of a volt DC when the engine is operating normally and in closed loop. For this test, it does not matter how long a sensor stays below .2 volts or above .8 volts. All that matters is how much time in milliseconds (ms) it takes for the sensors output voltage to cross the opposite threshold when it starts to change. Most manufacturers’ thresholds are .3 volts and .7 volts respectively.

To perform the job correctly you should look at the items that could have caused the reported failure of the sensor. This would include an inspection of the basic items, such as air filter, loose or broken air duct tubing, vacuum leaks, malfunctioning Positive Crankcase Ventilation (PCV) system, lack of maintenance, etc.

You should check for Technical Service Bulletins (TSB) including those that address the possible need to reprogram the Powertrain Control Module (PCM) that may relate to the Diagnostic Trouble Code (DTC P0133). If it needs reprogrammed that can be performed with J2534 tools such as ours.

After you are satisfied that no problems exist from the basic inspection, you should use a Scan Tool*, such as our 2x80 series scan tool with a good software package to view the data from the sensor to confirm the Diagnostic Trouble Code (DTC P0133).

If you confirm that its’ switching times are low, remove the sensor and inspect it for contamination. This is a non moving part so therefore it does not have parts that wear out. Its’ only enemy is contamination that coats the ceramic and reduces efficiency, so look again at the items in the basic list as something caused this failure. Do not allow yourself to replace this sensor, send the vehicle down the road only to have it return with the same problem.

Notes on sensors;

General Motors has an off car procedure to clean Oxygen Sensors for the OBD I vehicles. This procedure was implemented as an on car procedure through the use of an OTC Scantool. It has mixed results both ways. It was a worthwhile procedure from GM as it did reduce the number of  “warranty defects”. It was also worthwhile for the mechanic as GM paid for both the cleaning and the replacement as 2 separate procedures. The off car cleaning procedure has been tried on OBD II vehicle sensors with mixed results.

If you are replacing the sensor, do not be afraid to use the universal sensors from Bosch corporation as they are the same sensor as their direct fit, you just have to connect the wires properly.

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