Sensor mal reinstalado tras un cambio de filtro

A sensor that was removed to reach something else and put back wrongly — cross-threaded, not fully seated, its pipe kinked, its connector on the wrong one of a pair, or its harness routed against something hot. This is a repair-induced fault, and its diagnostic value is entirely in the timing: a code that appears within days of a service, in a system that was opened during it, has a much shorter list of likely causes than the same code arriving unannounced.

Swapping two identical sensors is the version that hides best. Where a system carries several sensors of the same part number in different positions, connectors are easy to interchange, and every individual reading is then perfectly valid — it is only the correlation between positions that is wrong. That is why the code so often names a correlation or a rationality check rather than a circuit, and why testing each sensor individually finds nothing wrong with any of them.

Ask what was disturbed before testing anything. A sensor whose reading is implausible for its stated position — one reporting a temperature that belongs further down the exhaust, or a pressure that belongs on the other side of the filter — is telling you where it actually is. Verify the routing against the diagram rather than against how it looks, because a swapped pair looks entirely normal.