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

What does P0133 mean?

The bank 1 upstream oxygen sensor is switching between rich and lean too slowly. Sensor 1 is the upstream sensor, mounted before the catalytic converter; the engine computer uses its signal to adjust fuel mixture. A sensor that responds slowly is usually aging or contaminated, and slow feedback makes fuel control less precise.

Generic OBD-II definition: O2 Sensor Circuit Slow Response (Bank 1 Sensor 1). Confirm applicability in your vehicle service information.

Common causes

• Old sensor that is slow to respond (the most common cause)
• Sensor contaminated by oil, coolant, or silicone
• Exhaust leak near the sensor
• Intake vacuum leak causing an unstable mixture

Symptoms

• Usually no change in how the car drives
• Gradual drop in fuel economy
• May fail emissions inspection

Can I keep driving with P0133?

Severity: Medium Drive gently and get it diagnosed soon.

If the check engine light is flashing or the car runs badly, stop driving and have it checked.

Typical fixes

• Watch the sensor's switching speed on a scanner; compare against bank 2 on V engines
• Look for signs of oil or coolant consumption that could foul a new sensor
• Replace the sensor after ruling out leaks