تسرب هواء في نظام إمداد محلول المعالجة

Air drawn into the reductant delivery lines, so the pump moves a mixture of fluid and air rather than fluid. The dosing system meters by volume, so air in the line means the quantity delivered is less than the quantity commanded — and the module cannot see the difference directly.

The result is under-dosing with a pump that appears to be working. Conversion efficiency falls, the module increases the commanded dose to compensate, and consumption rises without the exhaust chemistry improving. High dosing with poor conversion is the pattern, and it points at delivery rather than at the catalyst.

The leak is on the suction side and therefore invisible — a joint under vacuum draws air in without letting fluid out, so there is no wet patch and no white crystalline residue to find. Check the filter housing seal, the pickup in the tank, and any fitting disturbed at a recent service. A pressure that builds slowly and decays quickly is the measurable sign, and it distinguishes air from a genuine blockage.