P0133 fault code: front oxygen sensor slow response
Plain-language definition
O2 Sensor Circuit Slow Response Bank 1 Sensor 1
What does it mean?
The front oxygen (lambda) sensor (Bank 1, Sensor 1) measures the oxygen in the exhaust before the catalytic converter. Because the engine computer constantly adjusts the mixture based on this sensor, the sensor needs to respond quickly: when the mixture switches from rich to lean or from lean to rich, the signal should change right away too.
P0133 is stored when the engine computer finds that the sensor responds to these changes more slowly than expected. The engine computer usually runs this check after the engine has warmed up, under specific conditions such as driving at a steady speed. A slow response often shows that the sensor has aged or become contaminated.
There may be no obvious symptom while driving; sometimes only the check engine light comes on. Even so, because the engine computer will adjust the mixture less precisely, you may notice higher fuel consumption or a stronger exhaust smell.
How serious is it?
It's a Warning-level code and often points to a worn sensor. If the problem continues, fuel consumption may rise and, in the long run, the catalytic converter may be affected.
Severity is a guide; if the warning light is flashing or you notice symptoms while driving, have the car checked at a workshop.
Common general causes
- The oxygen sensor wearing out with age (high mileage)
- The sensor becoming contaminated for reasons such as the engine burning oil or losing coolant
- An exhaust leak ahead of the sensor
- The sensor heater not working well enough
- A poor contact in the wiring or connector
The list shows general causes; a workshop finds the actual cause on your car with a check.
Definitions by make
Some manufacturers record the same code under their own wording:
- Honda
- Rear Air/Fuel Ratio (A/F) Sensor (Bank 1, Sensor 1) Circuit Slow Response
Related codes
How does it appear in the 2dakika report?
O2 Sensor Circuit Slow Response Bank 1 Sensor 1
If the code is read as a confirmed (stored) fault, the report shows it with the "Warning" severity; in pending or past records, codes that don't request the warning light and aren't critical appear as "Info". If the engine computer stored them, the conditions when the fault was recorded (engine temperature, rpm, speed) are shown too.
Read this code with the OBD-X1, and clear it from the app after the repair.
Clearing the code doesn't fix the fault; if the problem persists, the code comes back.