These sensors are used by the engine’s computer to determine air/fuel ratios and catalytic converter health of your engine. If you have a 150, 200, or 250Hp engine, you have two O2 sensors per engine, one “pre-cat”, or before the catalytic converter in your exhaust flow, and a “post-cat” sensor after your cat.
In the marine environment, these sensors tend to wear out much faster than they do in the automotive world, so it’s best to be familiar with them, and how to change them. We have a more detailed writeup regarding this, including how to find more affordable sensors in the group guides at:
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