P0133: OBD-II Trouble Code: O2 Sensor Circuit Slow Response (Bank 1 Sensor 1)

P0133 Trouble code definition

P0133 O2 Sensor Circuit Slow Response

What the P0133 code means

Bank 1 Sensor 1 is a sensor that is used by the computer (ECM) to monitor the amount of oxygen exiting the engine. The ECM uses the signal from the O2 sensor to adjust the fuel and air ratio of the engine. The air fuel ratio is adjusted by the ECM to regulate the amount of fuel consumption and to limit the amount of air pollutants exiting the engine. The O2 Sensor will tell the ECM the air-fuel ratio by sending a voltage reading back to the ECM.

The variation of gas and air hitting the sensor should change the voltage output of the O2 Sensor.The O2 Sensor voltage output should change as quickly as you can press the gas pedal, because once you hit the pedal, the air-fuel ratio changes instantly.

P0133 indicates the ECM senses that the O2 Sensor is not changing its voltage output quickly enough to the changing air-fuel ratio. Hence why the P0133 trouble code definition is O2 sensor circuit “slow response” because the circuit is not reacting quickly enough.

What causes the P0133 code?

• A faulty O2 Sensor
• A leaking exhaust manifold
• An engine vacuum leak
• An open or short in the wiring of the O2 sensor
• Soot or oil buildup on the O2 sensor (excessive buildup will clog the ports the sensor uses to measure the air fuel ratio)
• A dirty mass air flow sensor
• Incorrect fuel pressure

What are the symptoms of the P0133 code?

• Engine stalling or misfiring
• Poor gas mileage
• Loss of engine power

How does a technician diagnose the P0133 code?

• Visually inspects the wires related to the O2 sensor for fraying and saturation from contaminants, such as oil

• Measures the voltage output of the O2 sensor by using a scan tool or multimeter

• Visually inspects the base of the sensor for soot saturation, heat stress, or oil deposits

• Checks the air intake and vacuum hoses for leaks

Common mistakes when diagnosing the P0133 code

• Overlooking the fact that a dirty mass air flow sensor can cause an O2 sensor circuit slow response

• Not cleaning the wires and electrical terminals of the O2 sensor

• Overlooking the fact that a leaking vacuum line or intake manifold leak may cause erratic O2 sensor voltage readings. Voltage readings which may set a code P0133

How serious is the P0133 code?

This particular code can be harmful to the environment because the O2 sensor is used to keep the amount of harmful pollutants being emitted by the engine to a minimum. The O2 Sensor keeps the amount of pollutants to a minimum by regulating the air-fuel ratio to a level where not much pollutant will be created.

The environment is more sensitive to exhaust pollutants than most would think, so it is best to replace a faulty O2 Sensor.

What repairs can fix the P0133 code?

• Usually a replacement of the oxygen sensor will fix the P0133 code.

• At times the sensor itself will not be causing the code P0133, so a technician must check for other faults such as vacuum leaks, a dirty mass air flow sensor, or leaks in the exhaust system.

Additional comments for consideration regarding the P0133 code

When diagnosing code P0133 be sure to check for vacuum leaks, intake leaks, and also check the mass air flow sensor for the buildup of oil or other contaminants to avoid the chances of a mis-diagnosis.

Need help with a P0133 code?

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