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P0133 Code – What Does It Mean & How To Fix It

This is one of the most frequent OBD2 trouble codes. Read the full article below to know what it means, how to fix it, and what other codes may show related to it.


Trouble code P0133 on an OBD-II scanner is defined as “O2 Sensor Circuit Slow Response (Bank 1 Sensor 1).”


Bank 1 Sensor 1 is used by the electronic control module (ECM) to monitor the amount of oxygen that is leaving the engine. The ECM uses the signals sent to it from the O2 sensor to adjust the fuel and air ratio of the engine. 

The ECM adjusts the air to fuel ratio to regulate the amount of fuel consumption. This is also to limit the number and quantity of air pollutants that exit the engine. The O2 sensor will tell the ECM the air-fuel ratio by sending a voltage reading back to the ECM.


There are several common causes of a P0133 trouble code. This can be due to a faulty O2 Sensor or a leaking exhaust manifold. This can also be registered by an engine vacuum leak. It is not uncommon for this problem or trouble code to be caused by an open or short in the wiring of the O2 sensor.

Soot and/or oil can easily buildup on the O2 sensor. This excessive buildup will clog the ports the sensor uses to measure the air to fuel ratio. A dirty mass airflow sensor can cause this as well. It is also common for a P0133 code to be caused by incorrect fuel pressure. 


There are several symptoms you should notice with a vehicle that could be suffering from a P0133 trouble code. The engine may start stalling or misfiring. You may notice that the vehicle begins to have poor gas mileage or that the engine begins to lose power. 


There are some steps that you need to follow carefully in order to properly diagnose a P0133 trouble code: 

  • Visually inspect the wires related to the O2 sensor for saturation or fraying from contaminants, like oil. 
  • Measure the voltage output of the O2 sensor by using a multimeter or OBD-II scan tool
  • Visually inspect the base of the sensor for soot saturation, heat stress, or oil deposits. 
  • Check the air intake and vacuum hoses for leaks.

In following the above process for diagnosis, you will more than likely avoid the common mistakes that are listed below when diagnosing a P0133 trouble code. 

Common mistakes

Here are some of the most common mistakes that are made when diagnosing and treating a P0133 trouble code: 

  • Overlooking a dirty mass airflow sensor and how that can cause an O2 sensor circuit to respond slowly. 
  • Not cleaning the wires and electrical terminals of the O2 sensor.
  • Failing to see that a leaking vacuum line or intake manifold leak can cause erratic O2 sensor voltage readings. Voltage readings which may set a code P0133

How serious is this?

This particular code can be harmful to the environment. The O2 sensor is used to keep the amount of harmful pollutants being emitted by the engine to an absolute minimum. The O2 sensor is able to do this by regulating the air-fuel ratio to a level where trace amounts of pollutants will be created. The environment is more sensitive to exhaust pollutants than many would think, so it is best to replace a faulty O2 Sensor as soon as possible.

What repairs can fix the code?

You can usually replace the oxygen sensor and that will fix this trouble code. There are certain times and occasions where the sensor itself will not be causing the code P0133. In these instances, the technician must check for other faults such as vacuum leaks, a dirty mass that is clogging the airflow sensor, or leaks in the exhaust system.

Related codes

None listed.


Due to the severity of this issue and the damage that it can cause the environment and potentially your vehicle if left untreated, this is a trouble code that should be properly diagnosed and addressed as soon as possible. Though this trouble code may not be detrimental to your vehicle, it can inhibit vehicle performance and be harmful to the environment. 

P0133 Code – What Does It Mean & How To Fix It