P0133O2 Sensor Circuit Slow Response Bank 1 Sensor 1
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Needs a drive cycle to confirm a fix
- How the car detects it
- The oxygen sensor before the catalytic converter on bank 1 (sensor 1) is the main control sensor for the mixture. It is either a switching sensor (about 0.1 V lean to 0.9 V rich) or a wide-band sensor that works with a pump current evaluated by an interface chip. P0133 means the sensor does not react fast enough to mixture changes. Methods differ fundamentally: GM measures passively how long the signal takes to cross 400–600 mV in each direction, averaged over 60 s; Ford forces the mixture to swing at 1.5 Hz and fails a switching sensor whose amplitude stays below 0.5 V, or evaluates response times of a wide-band sensor against a no-fault area; Subaru compares controller activity with measured lambda over 210 s. The test runs once per drive at warm part load; two trips. Mixture control usually stays active, but worse.
- What you may notice
- Check engine light on (after two drive cycles)
- Slightly higher consumption
- Higher emissions, possible emissions test failure
- P0420 may follow
- Likely causes
- LikelyAged, sooted or poisoned upstream sensor (oil, silicone, coolant, additives)
- PossibleExhaust leak ahead of the sensor (manifold gasket, crack)
- PossibleSensor heater weak or intermittent (sensor too cold)
- PossibleMixture fault: air leak, injectors, fuel pressure, air flow sensor
- RareWiring resistance or aftermarket sensor with different characteristics
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Easy · Often possible to do yourself.Typical cost: €60 – €300
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.