Q. How do I know if both upstream and downstream oxygen sensors (O2) are working well?

Create Date: Sept. 2, 2021, 9:21 a.m. (1)

How do I know if both upstream and downstream oxygen sensors (O2) are working well?, None|bekomcar.com

From above the first S2 is not working well. It should show rather a flat line instead of sine wave.

However, the second and the third S1 and S2 oxygen sensors are working well. Please note that job of S1 is to report oxygen level to engine control module (ECM). Job of S2 is check if catalytic converter is working good. Again, S2 reports the diagnosis result to ECM.

Upstream O2 sensor (S1), also called A/F ratio sensor, should show sine wave of up and down frequency between 0.1V~0.9V ranges. S1 is located before the catalytic converter. This is valid for common narrow band O2 sensors.

For downstream O2 sensor (S2) located after the catalytic converter, the scanned wave should look like a flat line within 0.6V~0.9V ranges. If S2 looks like that of S1, then it is either catalytic converter or O2 is malfunctioning.

Issue environments & Tags

TBC #Engine, #Diagnosis

Tutorial

Vehicle diagnostics, OBD2, DTC basics - 101 Bank1 sensor 1 oxgen sensor health status What O2 sensors and how many are there?

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SunJoo Moon , Edit Date: Dec. 27, 2021, 4:47 p.m.