02 sensor carbon build-up

JESSICA MERTENS

MEMBER
2011 HYUNDAI SONATA
2.4L
4 CYL
2WD
AUTOMATIC
160,000 MILES

When I was reading up on O2 sensors I read that from looking at the old O2 sensor you can tell what made it go bad by the buildup on it and that you should address whatever made it go bad in the first place. It said that carbon build-up would make it be black so I'm wondering what caused it.

Image (Click to make bigger)

1 Reply

JACOBANDNICKOLAS

MECHANIC
108,269 POSTS

Hi,

The black carbon on the sensor in the picture is normal. That is from the exhaust system. I'm not sure what was read, but if there was something like engine coolant getting into the system, that could cause the sensor to have a whitish color. Also, if the engine was running extremely lean (too much air/ not enough fuel) it would look very clean. If the engine was burning an excessive amount of oil, the entire thing would be black. I suspect that was what was meant.

As far as yours. chances are it just wore out and went bad internally.

Here are two links you may find of interest. The first discusses what the sensor is, how it works, and its purpose. The second explains how to test one.

https://www.2carpros.com/articles/how-an-oxygen-sensor-works

https://www.2carpros.com/articles/how-to-test-an-oxygen-sensor-02-sensor

I hope this helps answer your question, which is a good one.

Let me know.

Take care,

Joe