پمپ محلول اوره معیوب

The pump that pressurises diesel exhaust fluid and delivers it to the dosing injector. Its enemy is the fluid it carries: urea solution crystallises wherever it dries, so a pump that stands unused — a car doing short runs, or one parked for months — can seize on its own deposits rather than wear out.

Symptoms arrive as dosing faults rather than pump faults: pressure that will not build, dosing that stops mid-cycle, and a NOx exceedence attributed to interrupted dosing. Many designs run a purge cycle at shutdown to pull fluid back out of the lines; a pump that cannot purge fails its neighbours too, so a seized pump often arrives with a blocked injector beside it.