Cause
Oil or coolant contamination on the sensor tip
A sensor's tip coated with oil or coolant, insulating it from what it measures. The reading becomes slow rather than wrong, which is the important distinction: it looks plausible at steady state and lags whenever conditions change.
So correlation checks against a neighbouring sensor trip while each value alone seems reasonable. Where the contamination came from matters more than the sensor. Oil means a turbocharger seal, a failing breather or valve stem seals; coolant means an internal leak, and coolant on an exhaust sensor is a head gasket question rather than a sensor one. Inspect the tip on removal — the coating is visible and conclusive — and a new sensor into the same contamination is fouled again within weeks.
Typically specialist work. Needs equipment or training most home workshops do not have.
Codes this can cause (1)
Codes where this is a likely explanation first, rather than merely a possible one.
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