P1133 — HO2S Insufficient Switching (Bank 1 Sensor 1)
CAUTIONIs it safe to drive? Drive gently and get it looked at soon — it can worsen or fail inspection.
What P1133 means
This is a manufacturer-specific code — its meaning depends on the vehicle’s make (see below).
What P1133 means on specific makes
Heads up: P1133 is a manufacturer-specific code, so the same number means different things by make.
Chevy / GMC / Cadillac / Buick CAUTION
The front O2 sensor on bank 1 isn't switching rich/lean often enough in the time window the PCM expects (about 90 seconds of test) — the sensor is lazy or the mixture is off. Drivable, but worsens fuel economy and can lead to a P0420.
- Lazy/aging upstream O2 sensor ($50-150)
- Exhaust leak before the sensor ($50-200)
- Vacuum leak / lean condition ($0-200)
- Contaminated sensor (oil/coolant) ($50-150)
Check first: Watch the front O2 waveform live — if it's slow/flat-lining, replace the sensor; check for exhaust leaks near it.
Source: engine-codes.com P1133 Chevrolet / KBB / CarBuzz
Toyota / Lexus / Scion CAUTION
The A/F sensor responds too slowly to changes in exhaust mixture (sluggish switching), so the ECM flags it as worn. Common as these sensors age.
- Worn/slow upstream A/F sensor ($120-300)
- Sensor contamination (oil/coolant burn)
- Exhaust leak near sensor
Check first: Compare commanded vs actual A/F response on a scan tool during throttle changes; a slow trace means replace the sensor.
Source: troublecodes.net/toyota, toyotaspace.com