P0133: What it means and how to fix it
Learn what a P0133 code means and how to diagnose and fix it
A P0133 trouble code is defined as: “Oxygen Sensor Circuit Slow Response (Bank 1 Sensor 1).” Bank #1 is the portion of the engine that houses cylinder #1. Sensor 1 is the sensor located BEFORE the catalytic converter. The PCM expects to see a rapidly changing value from this sensor, a value that corresponds to the rapidly changing air/fuel mixture. When it doesn’t see rapid switching, it sets a P0133 code.
The PCM sends a reference voltage (usually 5-volts) to the variable resistor in the oxygen sensor and looks for a return voltage. It expects to see a rapidly changing return voltage varying from .1-volts to .95-volts. If the voltage doesn’t switch rapidly, the PCM will set a trouble code P0133.
What causes a P0133 trouble code?
The computer sets this code once the engine is in a closed loop for at least 60 seconds, the coolant is up to operating temperature, and the engine is running at 1,000-3,000 RPM. The computer looks at the amount of time the oxygen sensor takes to switch between a rich and lean reading. If the time is longer than 0.114 seconds, the P0133 trouble code is set.
Avoid this mistake when dealing with a P0133 code
A lazy oxygen sensor can cause a P0133 code to set. But a vacuum or exhaust leak can also cause this code to set. So check for exhaust leaks and vacuum leaks before you rush to replace the upstream oxygen sensor.
Keep in mind that this code is telling the computer that it’s not responding
Manifold Absolute Pressure Sensor
quickly enough. So the problem can be the sensor itself of an exhaust mixture that isn’t changing rapidly enough. For example: a leaking fuel injector and saturate the exhaust and prevent the oxygen sensor from seeing a rapid change.
Fuel Injector
A leaking fuel pressure regulator could cause the same condition. And, a bad MAP sensor that reporting the wrong engine vacuum can cause this. Check out all of those before replacing the oxygen sensor.
To learn how to replace an oxygen sensor, click here
© 2012 Rick Muscoplat
Posted on by Rick Muscoplat