OBD-II · Engine and powertrain (P)
P0133
Oxygen sensor slow response bank 1 sensor 1
What it means
The upstream lambda sensor responds too slowly to mixture changes.
Symptoms
- engine warning light
- higher fuel consumption
- possible hesitation or uneven running
- may fail the emissions part of the roadworthiness test
Likely causes, most likely first
| No. | Cause |
|---|---|
| 01 | aged lambda sensor |
| 02 | sensor contamination |
| 03 | exhaust leak |
| 04 | lazy fuel trim correction |
| 05 | wiring resistance |
What to check, step by step
- 01Fix any misfire or fuel-trim codes first
- 02Check for exhaust leaks near the sensor
- 03Watch the sensor response to a quick throttle blip in live data and compare with a known-good sensor
- 04Look for contamination sources: oil burning, coolant loss, silicone sealant, fuel additives
- 05Replace the sensor if it is old or contaminated