P0133: Upstream oxygen sensor on bank 1 reacts too slowly
O2 sensor circuit slow response (bank 1 sensor 1)
Severity: Severity not verified — if the car runs badly, have it inspected
Our sources list stalling, misfires, poor mileage and lost power as symptoms but do not rate how safe it is to drive.
It gets more serious if:
- Inspect soon: Inspect soon if the engine stalls, misfires or loses power.
P0133 in short
P0133 means the upstream oxygen sensor on bank 1 is switching between rich and lean too slowly. Causes include an aging sensor, an exhaust or vacuum leak, wiring faults and a dirty airflow sensor. Expect poorer fuel economy. Have it checked soon, since severity is not verified.
The upstream sensor should flip quickly between rich and lean readings as the computer adjusts the mixture. If it responds too slowly, the computer sets P0133.
PartsAvatar lists a faulty sensor, an exhaust manifold leak, a vacuum leak, wiring open or short, soot or oil on the sensor, a dirty airflow sensor and incorrect fuel pressure. Symptoms are stalling or misfiring, worse fuel economy and power loss.
Saturn and Honda bulletins from the late 1990s cover P0133 on specific models, so ask a dealer about your VIN.
Most likely causes
Cause 1: Aging or contaminated upstream oxygen sensor
Common general cause- Why it ranks here
- PartsAvatar lists a faulty sensor first and soot or oil build-up, and says replacement often clears it.
- What would change this
- Rises if live data shows slow or lazy switching. Falls if switching is quick.
Cause 2: Exhaust or vacuum leak near the sensor
Common general cause- Why it ranks here
- PartsAvatar lists exhaust manifold and vacuum leaks as ways to cause slow response.
- What would change this
- Rises if a leak is found or fuel trims are off. Falls if exhaust and intake hold.
Cause 3: Dirty airflow sensor or incorrect fuel pressure
Possible — needs testing- Why it ranks here
- PartsAvatar lists these, but they typically set other codes too.
- What would change this
- Rises if fuel trim or airflow codes are stored.
Cause 4: Known model software or sensor issue (some Saturns and Hondas)
Supported by vehicle data- Why it ranks here
- Saturn's 1999 S-Series bulletin covers P0133 on DOHC automatic models, and Honda has a 1998 Civic bulletin for it.
- What would change this
- Rises on those models. Falls on others.
Cause 5: Sensor wiring open or short
Possible — needs testing- Why it ranks here
- PartsAvatar lists wiring faults, which usually set circuit codes too.
- What would change this
- Rises if the signal drops out when the harness is moved.
What to test first
Start at step 1. Each result tells you what it means and where to go next.
Step 1: Read all codes and fuel trims, and check the exhaust and intake for leaks.
IfFuel trims are off or a leak is found
It meansFix the leak first.
IfTrims are normal
It meansCheck the sensor's live switching.
Step 2: Watch the upstream sensor's live data at warm idle and light throttle.
IfSwitching is slow or flat
It meansReplace the sensor.
IfSwitching is quick
It meansCheck wiring and bulletins.
Symptoms
- Check engine light
- Worse fuel economy
- Stalling or misfiring Gets more serious: stop and have it checked.
- Reduced power
How to fix
Step 1: With the engine off and cool, look for loose or cracked vacuum hoses and a damaged exhaust near the sensor.
Parts and cost context
- Oxygen (O2) sensor:Replacing the upstream sensor is common. Confirm leaks first. Labour varies; get a quote.
Labor varies by vehicle and shop; get a quote before you approve a repair.
Compare used part prices on PartPriceGuideOn your vehicle
HondaYour car
1998 · Civic
Supported by vehicle dataHonda bulletin 99049 covers a check engine light with P0133 stored in the PCM on the 1998 Civic. Whether it is still current is not verified.
1998–2000 · Accord
Supported by vehicle dataHonda bulletin 00017 covers this code: mIL with P0133 primary heated oxygen sensor slow response, Accord. Whether it is still current is not verified.
99049Status unverified
MIL on with DTC P0133 stored in the PCM
1998civic · NHTSA 606126
Check engine light with P0133 stored. The NHTSA summary does not give the repair.
We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.
00017Status unverified
MIL with P0133 primary heated oxygen sensor slow response, Accord
1998–2000accord · NHTSA 610601
Check engine light with P0133 (primary heated oxygen sensor slow response) stored on 1998-2000 Accords.
We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.
AcuraYour car
1998–1999 · RL
Supported by vehicle dataAcura bulletin 99025 covers this code: mIL on with P0133 or P0153 stored, RL and TL. Whether it is still current is not verified.
99025Status unverified
MIL on with P0133 or P0153 stored, RL and TL
1998–1999rl, tl · NHTSA 606303
Check engine light with P0133 or P0153 stored on 1998-1999 Acura RL and TL.
We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.
MitsubishiYour car
2001 · Diamante
Supported by vehicle dataMitsubishi bulletin 011001 covers this code: p0133 oxygen sensor circuit slow response, Diamante. Whether it is still current is not verified.
011001Status unverified
P0133 oxygen sensor circuit slow response, Diamante
2001diamante · NHTSA 627224
Information on P0133 oxygen sensor circuit slow response on the 2001 Diamante.
We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.
SaturnYour car
2000 · S-Series
Supported by vehicle dataSaturn bulletin 00T02 covers this code: service engine soon with P0133, 2000 S-Series. Whether it is still current is not verified.
99T66Status unverified
Service engine soon light with P0133 O2S slow response sensor 1
1999s-series · NHTSA 609896
DOHC engines with automatic transaxles and federal emissions may show P0133. The NHTSA summary does not give the repair.
We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.
00T02Status unverified
Service engine soon with P0133, 2000 S-Series
2000s-series · NHTSA 609906
Some 2000 Saturn S-Series show the service engine soon light with P0133 (O2S slow response, sensor 1).
We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.
Related codes
P0133 questions
Should I replace the oxygen sensor for P0133?
Often, but check for exhaust and vacuum leaks and fuel trim first.
Sources and review
- OBD Code P0133 - O2 Sensor Circuit Slow Response (Bank 1 Sensor 1)
- Saturn 99-T-66, service engine soon light with P0133 O2S slow response sensor 1
- Honda 99-049, MIL on with DTC P0133 stored in the PCM, 1998 Civic
- Acura 99025, MIL on with P0133 or P0153 stored, RL and TL
- Honda 00017, MIL with P0133 primary heated oxygen sensor slow response, Accord
- Mitsubishi 011001, P0133 oxygen sensor circuit slow response, Diamante
- Saturn 00T02, Service engine soon with P0133, 2000 S-Series
- Last reviewed
- Written by
- Saurabh K.
- Editorial review
- Pending
- Technician review
- Technician review pending
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