Will P0133 fail an emissions test?

Yes in most cases. A slow-responding sensor causes the OBDII readiness monitor for the O2 sensor to fail, which is an automatic emissions failure in most US states.

How long do upstream O2 sensors typically last?

Most heated oxygen sensors last 80,000 to 120,000 miles. Engines that burn oil or use contaminated fuel see shorter sensor life.

Can a slow O2 sensor cause a P0420 catalyst code?

Indirectly, yes. A slow upstream sensor can make a healthy converter appear inefficient because the upstream and downstream switching patterns look more similar than they should.

Codes › P0133

P0133: The upstream oxygen sensor on the left side is responding too slowly

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

Moderate severityCan you keep driving?

Yes. A slow-responding sensor still provides some feedback. Fuel economy and emissions will suffer but the engine will not be at immediate risk. Schedule a repair within a few weeks.

What it means

A healthy upstream O2 sensor switches between lean and rich rapidly, typically more than once per second at operating temperature. P0133 means the sensor is switching, but too slowly. The ECM measures switch frequency and flags it when the sensor takes more than 100 milliseconds to cross the 0.45V midpoint. A slow sensor causes the ECM's fuel control loop to lag, running the engine slightly rich or lean for longer periods than normal. Sensor age and contamination are the leading causes.

Common causes

Aged or contaminated O2 sensorThe most common cause on vehicles over 80,000 miles. The sensing element slows down with age and contamination.
Faulty heater element causing slow warm-upA partially working heater takes longer to bring the sensor to operating temperature, making it appear slow early in the drive cycle.
Exhaust leak near the sensorDiluted exhaust samples cause the sensor to switch more slowly than it would with clean exhaust.
Silicon or phosphorus contaminationRTV silicone used near intake components or contaminated fuel can coat the sensor and slow its response.

What it costs

Upstream O2 sensor replacement$150 to $380
Exhaust leak repair$100 to $400

Symptoms

Check engine light on
Marginally reduced fuel economy
Slightly rich or lean fuel trims
Emissions test failure for excessive hydrocarbons
No noticeable driveability complaint in most cases

What to do next

P0133 almost always requires sensor replacement. Cleaning cannot restore a slow O2 sensor element. Before ordering the part, check for an exhaust leak near the sensor, since a leak is a cheaper fix and can cause this code. On vehicles past 100,000 miles, the sensor is likely worn and replacement is the appropriate step. Use a quality OEM-equivalent sensor, not a bargain replacement.

Lewis shows the live O2 sensor switching waveform so you can measure switch frequency directly and confirm the sensor is switching slowly rather than stuck. Download Lewis.

Related codes

FAQ

Will P0133 fail an emissions test?: Yes in most cases. A slow-responding sensor causes the OBDII readiness monitor for the O2 sensor to fail, which is an automatic emissions failure in most US states.
How long do upstream O2 sensors typically last?: Most heated oxygen sensors last 80,000 to 120,000 miles. Engines that burn oil or use contaminated fuel see shorter sensor life.
Can a slow O2 sensor cause a P0420 catalyst code?: Indirectly, yes. A slow upstream sensor can make a healthy converter appear inefficient because the upstream and downstream switching patterns look more similar than they should.