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[SentraMench]

The O2 sensor in my gf's 96 Sentra 1.6 L has an orange/brown
discoloration on one side of the tip that samples the exhaust stream.
Is this normal? Or does it indicate improper combustion? She is using
a lot of coolant, whichh I think is being burned in the engine, since I
can't find any external leaks.

She is getting the 0303 MIL code for O2 sensor, but I think the
exhaust stream might be to blame, not the O2 sensor itself, since the
exhaust has the effluent of the burning coolant.

Comments?

Thanks