RE: help with engine code P1685 invalid skim
DTC P1685 is Invalid SKIM Key. The Sentry Key Immobilizer Module (SKIM) is part of the security system and kills the vehicle when a wrong key is used. There may be a problem with your key or the chip reader in the ignition switch. This is something the dealer will need to determine for sure. This code will also be set if someone actually tried to steal the vehicle.
My guesswould beto reset your PCM (unhook bat. and depress brake for 1 min), then try to start the car. If that doesn't work, I guess haul it into a dealership so they can run a diagnostic