The test includes handling of AdBlue which is highly corrosive to metal,copper and aluminum. AdBlue quickly oxidizes metal and creeps into the wiring. Cleaning with water or compressed air is ineffective. Make sure that all connectors are connected and protected from splash of AdBlue and from AdBlue that is dosed out of the dosing valve. If you spill AdBlue on an unprotected connector, you must replace the connector immediately.