Time-Consuming Problems:
Common scenarios which often require more than one hour of diagnostic time:
Intermittent problems: can be difficult to duplicate. See the EDS policy on intermittent problems.
CAN Network & Communication problems: since there can be literally dozens of modules on one network, a communication problem can be very time-consuming to pinpoint, especially if the modules are hard to access for testing.
Parasitic battery draws, shorted/open wires in harness: can be time-consuming to track down, especially if interior or exterior panels have to be removed for proper access.
Aftermarket accessories: alarm systems, remote start, snow plow/brake controllers, lighting, tuners etc. may be interfering with stock vehicle operation.
Improper previous repairs: faulty aftermarket components, improper harness routing, splicing, etc. may have to be repaired before the actual diagnosis can begin. Sometimes correcting improper repairs solves the initial problem!
European vehicles: are generally more complex and require more disassembly to access components and wiring. European OEM information and wiring diagrams are at times difficult to obtain and use.
Rare or classic vehicles: as with European makes, proper information (diagnostic procedures, wiring diagrams, etc.) is often difficult to obtain for classic or rare models.