my car will go on a long trip and then does not want to start

Hello, "the mechanics" shouldn't be solely using "their device" - because diagnostic trouble codes are not likely to be set by what is happening, and although monitoring components is possible with some diagnostic tools -- only the Hyundai GDS tool (and equivalent) are really dialed into the different components of your Hyundai for analysis. That said, it's more likely that hands on diagnostic testing of the ignition key cylinder, ignition electrical switch and all wiring related including battery cables and connections is needed. Another thought would be related to the transmission gear shit selector. If the car does not see the transmission in "park" or "neutral" gear, it will not allow the engine to crank either. This sensor and harness should be checked in the event that figures in. www.repairpal.com/repair-shops