Generic OBD2 code · Emissions / oxygen sensors

P0133: O2 Sensor Circuit Slow Response (Bank 1, Sensor 1)

The engine computer has found that the upstream oxygen sensor on bank 1 takes too long to switch between rich and lean readings.

CodeP0133

SystemEmissions / oxygen sensors

Typical urgencyModerate

Can I keep driving?Usually drivable short term, but fuel economy and emissions can suffer, so diagnose it soon.

What does P0133 mean?

Bank 1 sensor 1 is the oxygen sensor before the catalytic converter on the side of the engine with cylinder 1. The ECM uses it to trim fuel delivery in real time.

A healthy upstream sensor switches quickly between rich and lean as the ECM adjusts the mixture. When the switching becomes too slow, the ECM cannot control the mixture as precisely and stores P0133.

Common symptoms

Check engine light on
Possible decrease in fuel economy
Rough idle in some cases
Often few other symptoms

Common causes

The causes below are the ones commonly seen with P0133. The actual cause can vary by vehicle, engine and mileage, so treat this list as a starting point, not a diagnosis.

An aged or contaminated oxygen sensor
An exhaust leak ahead of the sensor
An intake air leak
Wiring or connector problems at the sensor

What to check with a scanner

In Live data, graph bank 1 sensor 1 at a steady 2,000 to 2,500 rpm. A healthy sensor switches quickly; a lazy one moves slowly.
Where supported, check Mode 06 results for the oxygen sensor monitor.
Listen and look for exhaust leaks near the front pipe and manifold.
Check fuel trims for signs of an intake leak.

How to read and clear P0133 with OBD Master Pro

Plug in your adapter. Connect a generic ELM327 (or ELM329) OBD2 adapter to the diagnostic port, usually under the dashboard on the driver's side. Bluetooth Classic, Bluetooth LE, Wi-Fi and USB OTG adapters are supported.
Switch the ignition on. Turn the key to ON or start the engine, depending on your car.
Connect in OBD Master Pro. Open the app, go to Connection and pick your adapter. Classic Bluetooth adapters connect from the Bluetooth tab, Bluetooth LE adapters from the BLE tab with no pairing needed. Use the generic OBD2 / EOBD profile or your car's brand profile.
Read the codes. Open the fault codes screen to see stored, pending and permanent codes. Confirm P0133 is listed and note any other codes, since they often explain the cause.
Check the details. Look at freeze frame data, Live data and, where your car supports it, Mode 06 test results (see the checks above).
Fix, then clear. After the repair, clear the codes to turn off the check engine light. Clearing also resets the emissions readiness monitors, so drive normally and check the readiness screen before any inspection. Permanent codes cannot be erased with a scan tool; they clear on their own once the car's self test passes.

Tip: you can also look up P0133 and other codes in the app's DTC search without connecting to a car. If your adapter will not connect, use Connection > Share connection log and email it to support. Many cheap ELM327 clones only handle basic engine OBD2, which is all you need for P0133.

When to see a mechanic

Get professional help if any of these apply:

You hear an exhaust leak near the manifold
The code returns after replacing the sensor
Several oxygen sensor or fuel codes are stored together

If you are unsure, a qualified technician can confirm the cause with tests such as smoke testing, pressure testing or scope readings. Clearing a code does not repair the fault.

P0133 FAQ

Does P0133 mean the oxygen sensor is bad?

Often, but not always. Exhaust leaks, intake leaks and wiring faults can cause the same code, so check those first.

Can I drive with P0133?

Usually yes for a short time. Fuel economy and emissions can be affected, so plan to fix it.

Where is bank 1 sensor 1?

It is the upstream oxygen sensor, before the catalytic converter, on the side of the engine that contains cylinder 1.

Check P0133 on your own car

OBD Master Pro turns your Android phone and a generic ELM327 adapter into a code reader: read and clear codes, view freeze frame and live data, and check emissions readiness.

Sources

Published October 24, 2026. Updated October 24, 2026. This guide is general information for generic SAE codes. Always follow the service information for your specific vehicle.