Capteur de dégradation du catalyseur d'ozone défectueux

The sensor used to judge whether the radiator's ozone-converting catalytic coating is still working, as distinct from the temperature sensor that reports whether it is warm enough to work. The two fail independently and produce different codes on the same system.

The distinction matters because this one feeds a verdict. A temperature fault means the module cannot tell whether the catalyst is in its window; a deterioration fault means it cannot tell whether there is any working catalyst there at all — and when it does reach a conclusion, that conclusion is P2577, a code whose wording is close enough to P0420 that it gets mistaken for a catalytic converter condemnation. Establishing that this sensor is telling the truth is therefore worth doing before anything is replaced on its say-so.

Everything about its location applies as for the temperature sensor: front of the vehicle, in the road spray and salt, so connector corrosion, chafed wiring and a plug left unmated after front-end work outrank genuine sensor failure by a wide margin.

No driveability consequence whatever. The cost of leaving it is an emissions monitor that cannot complete, and an intermittent fault here is the version most likely to prevent a test being taken at all, because each dropout interrupts the monitor before it finishes.