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

What it means

The upstream oxygen sensor on bank 1 switches between rich and lean more slowly than the calibrated response time. The ECM measures the time the signal needs to travel between its low and high thresholds and compares it with the specification, so a healthy sensor normally crosses several times per second at idle. A lazy sensor blurs mixture control, which increases fuel consumption and emissions and can eventually damage the catalytic converter.

Likely causes (most common first)

1. Normal ageing and soot build-up on the sensor element
2. Sensor poisoned by silicone sealant, leaded fuel, coolant or oil
3. Small exhaust leak near the sensor diluting the sample gas
4. Heater circuit weak, so the sensor works below optimum temperature
5. High resistance in the signal wiring or a corroded connector
6. Intake leak or fuel pressure fault causing wide mixture swings

Can you drive with it?

The car drives normally, so plan a sensor replacement at the next convenient service rather than urgently.