نصب واشر فاصله‌انداز روی سنسور

A spacer fitted between an oxygen sensor and its boss to move the element out of the exhaust stream. They are sold to suppress catalyst efficiency codes by making a downstream sensor see a diluted sample, and they are a defeat device rather than a repair.

The module is being lied to, and it often detects it: a downstream sensor that responds too slowly or sits at an implausible value produces rationality codes of its own — so the spacer that was fitted to clear one code sets another. It is worth recognising because the diagnosis is otherwise baffling: the sensor tests fine and reads wrongly. Look at the sensor's installation — a spacer is visible immediately — and note that in most jurisdictions defeating an emissions monitor makes the vehicle illegal for road use.