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P1133 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.


HO2S Insufficient Switching Bank 1 Sensor 1


This error code may not apply to every vehicle. It is a manufacturer-specific trouble code. Instead, it applies only to specific makes of cars, such as Buick, Chevrolet, GMC, General Motors, Toyota, Isuzu, etc. Specifications for definitions, troubleshooting, and repairs still differ from one model to another.

PCM (powertrain control module, also known as engine control module) monitors a variety of mechanics inside the engine and the vehicle, including the HO2S (Heated Oxygen Sensor). After the closed-loop operation begins, it monitors the HO2S’s activity for 90 seconds. By counting the number of HO2S-1 Lean/Rich (L/R) and Rich/Lean R/L switches, the PCM can evaluate the HO2S.


These error codes can be caused by multiple factors, including:

  • Sensor 1 of Bank 1 of HO2S is not working
  • Bank 1 of HO2S has an open or shorted harness
  • There is a problem with the electrical connection in bank one of the sensor 1 of HO2S
  • Leak in the vacuum system


When the P1133 code is activated, the Check Engine light will illuminate, and the code will be saved to the vehicle’s memory system.

  • An illuminated check engine light indicates there is a problem.
  • Engine starting is difficult.
  • Consumption of fuel has increased.
  • Black smoke is released in large amounts from the exhaust.


Track the short– and long-term values of the fuel trim – The short and long term fuel trim values can be captured using a scan tool if you have access to one.  This process requires you to warm up the Spark’s engine first.  When you take a look under the hood, you will be able to tell if the O2 sensor is operating within specifications.  Using your scan tool, you should compare the results to the manufacturer’s specifications.

The O2 Sensor’s wiring harness should be checked – Having one oxygen sensor on a bank isn’t easy. The hot exhaust right there affects it, and engine vibration increases its workload as well. Compared to almost any other wiring harness in an automobile, the sensor is most prone to failure.The wiring should be checked for burns or fraying. Inspect the sensor’s cable to ensure that it is snugly plugged in and there is no damage. Using a flashlight, this can be accomplished pretty quickly. Usually, detecting oxygen does not require disassembling anything.

Leaks from exhaust/vacuum systems – The Spark’s engine is often allowed to run with unmetered air due to worn or brittle vacuum lines.  Creating a lean environment is the result of this situation. A vacuum leak can be tested around the vacuum lines and the intake manifold.  Intake/vacuum lines can be cleaned by spraying carb cleaner around them.  The engine revs higher when the spot is found, regardless of throttle input. Carbamate cleaners are flammable defying all common sense.  Thus, you should BE CAREFUL.  Ensure you are equipped with a fire suppression system.

What repairs can fix the code?

Typically, faulty heated oxygen sensors cause this code. It should be checked and replaced if determined to be defective. Among the other repairs are:

  • Leaks in vacuum systems need to be repaired
  • A broken or shorted HO2S bank 1 sensor harness must be repaired or replaced
  • HO2S bank 1 sensor 1 has a poor electrical connection that needs to be repaired or replaced

Related codes

P1134 – “HO2S Transition Time Ratio Sensor 1”, –  An upstream oxygen sensor registers richness to leanness to richness during the period when the sensor is monitored, based on the average number of switches the sensor makes. The underlying definition may be rendered by another code than P1134 by some manufacturers. If you are unsure about the codes that apply to your application, consult the manual for it.


Diagnostics for P1133 can be costly. Depending on your location, vehicle’s model, and engine type, the auto repair’s diagnosis time and labor rates may differ. Typically, auto repair shops charge $75-150 per hour. Additionally, the code P1133 may also have definitions assigned by manufacturers that are unrelated to the number of times the oxygen sensor switches.

P1133 Code – What Does It Mean & How To Fix It