P0133 – O2 Sensor Circuit Slow Response

The P0133 code indicates that the Engine Control Module has detected a slow response time from the Oxygen Sensor installed in the Bank 1 Sensor 1 position. Along with a Check Engine Light, this could be accompanied by a drop in fuel mileage, smoke exiting the tailpipe, or a poor idle.

Although most times there will be no symptoms outside of a Check Engine Light. Continue reading for information on how to diagnose and repair this problem before it causes future costly repairs.

P0133 Definition

P0133 Definition (Generic): O2 Sensor Circuit Slow Response Bank 1 Sensor 1

P0133 ToyotaCode Definition: H02S11 Circuit Slow Response

P0133 Ford Code Definition: O2 Sensor Circuit Slow Response Bank 1 Sensor 1

P0133 VWCode Definition: H02S11 Circuit Slow Response

P0133 Dodge Code Definition: O2 Sensor Circuit Slow Response Bank 1 Sensor 1

P0133 Code Meaning

Modern vehicles are equipped with many sensors that send information based on engine operating conditions to the Engine Control Module. These inputs are then processed by the ECM to make adjustments to various outputs to keep the engine running as efficiently as possible. This is why modern vehicles are capable of making higher horsepower, while still getting great fuel mileage and meeting strict emission requirements.

The Oxygen Sensor is a very important input to the ECM as it detects the amount of oxygen in the exhaust stream and allows the ECM to make adjustments to the air/fuel ratio to keep the engine running smooth and efficient. The O2 sensor related to Code P0133 is in the upstream position (mounted before the catalytic converter) and on bank1. If the car is a 4 cylinder, there is generally only 1 bank. If you are dealing with a “V” style engine you will need to consult service information to verify which side of the exhaust is Bank 1.

An upstream oxygen sensor that is operating properly should constantly be switching back and forth between 0 volts and 1 volt. When the ECM detects that the sensor is not switching rapidly enough or not responding quickly to different driving conditions it will store a P0133 trouble code.

Causes Of P0133

Outside of the Check Engine Light being illuminated, it’s very possible that there won’t be any noticeable symptoms. But some more severe cases may include:

  • Smoke exiting the exhaust Reduced fuel economy
  • A drop in fuel mileage
  • A loss of engine power
  • Rough idle

Is The P0133 Code Serious?

Generally, the P0133 code is not severe. Although, it should be diagnosed and repaired as soon as possible. You may not notice any symptoms while driving, but it can cause your car to run at an incorrect air/fuel ratio and result in excess harmful tailpipe emissions. You will not be able to pass a state emissions test with this code present and by ignoring it you could eventually cause Catalytic Converter failure which can be a very costly repair.

Diagnosing And Fix Guide for The P0133 Code

You can you the OBD2 scan tool to diagnose the P0133 code
The P0133 code can be diagnosed with an OBD2 scan tool

The easiest way to diagnose P0133 is to use an OBDII scan tool. The first step in your diagnosis should be to record the freeze frame data related to P0133. This will show you the operating conditions present when the ECM stored the fault. Once you have the freeze frame data a simple visual inspection of the oxygen sensor wiring should be performed. Look for any frayed, broken, or melted wires. Check the wiring connector for moisture or corrosion. Unfortunately, oxygen sensor wiring cannot be repaired (unless it is for the heater circuit), so if you find damaged wiring the sensor will need to be replaced.

Next, run the engine and listen for any exhaust leaks before the sensor. Smaller leaks around the exhaust manifolds can be more evident on a cold engine, due to thermal expansion. This can also be accompanied by visual inspection of the exhaust system. In some rare instances, I have had leaks that I could not hear or see, but have found using a smoke machine installed in the tailpipe. This reveals very small leaks in porous welds that can cause oxygen sensor related codes. If any leaks are found, repair and clear codes.

Once you have verified the wiring is not damaged and there are no exhaust leaks you will need to access the data stream for the ECM using a scan tool. Here you can monitor the voltage coming from the oxygen sensor to the ECM. The voltage here should be constantly switching between 0 and 1 volt. If you are working with a “V” style engine you can compare bank 1 with bank 2 to see if one is switching faster than the other.

Next monitor the voltage at 2,000 RPMs then quickly close the throttle, then snap it open. When the throttle closes you should see voltage close to 0, and when it opens up again you should see close to 1 volt. This should all happen very quickly, under 100 milliseconds. Again, if you have an engine with 2 banks you can compare the 2 sides to see if one responds slower than the other. If the sensor fails either of these tests, replace the sensor.

These tests can also be performed by using a digital volt ohmmeter or lab scope and back probing the signal wire at the O2 sensor connector or ECM. You will need to consult a wiring diagram to identify which wires are correct. Also, using the diagram, find and verify that the sensor has a solid ground.

How to fix the P0133 code

What Mistakes To Avoid When Diagnosing The P0133 Trouble Code

A common mistake to avoid during diagnosing P0133 is to ignore the Mass Airflow Sensor. Removing the sensor and verifying that it is clean is usually enough for a P0133. And remember to double and triple check for exhaust leaks.

How To Avoid P0133

Keeping your exhaust system in good working order is imperative for proper oxygen sensor operation. Keeping your engine in the good mechanical condition is also very important, as excess fuel or oil getting into the exhaust stream can contaminate oxygen sensors.

Read More: P0131 Code: Meaning, Symptoms, Causes, Diagnostics, and Fixes