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

P0133 means the upstream oxygen sensor is switching too slowly between rich and lean. It's an aging-sensor code — contamination or simple wear is the usual cause.

Cost range: $150–$450. Severity: low. Safe to drive? Yes. Expect a modest fuel economy penalty and a likely emissions test failure.

Most common causes of P0133

1. Aged or contaminated O2 sensor — Silicone, coolant or oil contamination slows the sensor. ($150–$400)
2. Exhaust leak near the sensor — Disturbs the exhaust gas sample. ($100–$400)
3. Sensor heater circuit degradation — The sensor never reaches operating temperature quickly. ($150–$400)

Symptoms drivers report with P0133

• Failed emissions test
• Slightly worse fuel economy
• Check engine light only