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P1133 Error Code – What Does it Mean and How to Fix It

  • Cars Explained
  • Renee Martin
  • 4 minutes

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Do you notice a black smoke exiting from your exhaust? Do you have trouble starting your engine, and the OBD II scanner displays P1133 code while inspecting? P1133 error code is triggered when there’s a heated oxygen sensor. Don’t worry – here’s everything you need to know to resolve error code P1133.   

What is the P1133 trouble code?    

The code is defined as HO2S (Heated Oxygen Sensor) Insufficient Switching Sensor 1. Engine code P1133 is a manufacture-specific code and does not apply to all vehicles. The code is specific to vehicles such as GM, Toyota, Buick, Chevrolet, Isuzu, GMC, etc. Also, the definition, troubleshooting methods, and repair techniques can vary from one make and model to another.  


What triggers the trouble code P1133?   

The PCM (powertrain control module), also known as the engine control module in a vehicle, monitors multiple mechanics inside the engine and the vehicle – this includes the HO2S.   

The PCM monitors the HO2S for 90 seconds after the closed-loop operation begins. Then, the PCM evaluates if the HO2S is working properly by counting the number of HO2S-1 Lean/Rich (L/R) and Rich/Lean R/L switches. So, when the PCM finds the front HO2S unable to switch enough times, this triggers the error code P1133.  

What causes error code P1133?   

Multiple causes could trigger the code. Here are the most common factors:  

  • Bank 1 of HO2S has an open or shorted harness  
  • Sensor 1 of Bank 1 of HO2S is not working  
  • An issue with electrical connection in bank 1 of the sensor 1 of HO2S  
  • Leak in the vacuum system  
  • Disconnected, damaged, or burnt wiring and/or connectors  
  • Defective oxygen sensors  

What are the symptoms of P1133?   

Here are some of the most commonly reported P1133 error code symptoms:  

  • An illuminated check engine light   
  • Trouble in starting the engine   
  • Increased fuel consumption and decreased mileage.  
  • Large amounts of black smoke from the exhaust.  

P1133 error code

P1133 diagnosis 

Check valves: The first step is tracking the fuel trim’s short- and long-term values using a scan tool. For this process, you first need to warm up the engine. Next, look under the hood to see if the O2 sensor operates within specifications. Now, use the scanner to obtain the results and compare them with the manufacturer’s specifications.  

Check wiring harness: Another way to diagnose the issue is by checking the wiring harness of the O2 sensor(s). The sensor could be damaged because of the hot exhaust or the vibrations from the engine. That’s why it’s best to check them occasionally. Inspect the sensor cable to make sure it is snugly plugged in, and there is no damage.   

Check for leaks from exhaust/vacuum systems: If you’re getting professional help, the technician will look for exhaust/ vacuum systems leaks. This is a difficult step; therefore, it’s best to let experts deal with it. 

How to repair the P1133 error code?  

In most cases, a faulty heated oxygen sensor causes the code. If that’s the case, it needs to be checked and replaced. Here are other possible repairs the mechanic could perform:  

  • Repair the leaks in vacuum systems   
  • Replace the broken or shorted HO2S bank 1 sensor harness   
  • Repair or replace the poor electrical connection in HO2S bank 1 sensor 1  

How serious is the P1133 code?   

The P1133 trouble code issue is a problem in the oxygen sensors. This could ultimately affect the air to fuel ratio in your vehicle. It’s best to repair the code as soon as possible to avoid mileage and performance-related issues.

How much does P1133 repair cost?  

On average, the repair can cost you anywhere between $80 to $160 per hour – these are just labor rates. Of course, the cost can differ based on your vehicle type, model, and engine type. 

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