Various embodiments of methods, apparatus and systems that diagnose and/or detect faults of an electro-hydraulic control system for a transmission are presented. Some embodiments, adjust a main line pressure of the electro-hydraulic control system and detect faults based upon changes in a pressure switch resulting from such adjustments of the main line pressure. The pressure switch may be incorporated into a control main valve or a clutch trim valve of the electro-hydraulic control system.